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Editor Work2019 Vol. 27, No. s1
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Based on the analysis of the geological factors influencing the construction of sponge city in Tianjin, We have established the evaluation index system of the geological suitability for the construction of sponge city in the south plain area of Tianjin; AHP method was used to assign the weight of evaluation index for the geological suitability of sponge city construction, than the comprehensive scoring method was used to score the influencing factors, and ARCGIS was used to carry out the weighted superposition of the two, finally realizing the geological suitability zoning of sponge city construction in Tianjin; combined with the overall score, distribution range and regional nature of each district, this paper gives the LID facilities type suitable for the construction of sponge cities in south Tianjin plain area. The results show that the geological suitability of sponge city construction in the central city of Tianjin(including four areas around the city) and the Binhai new area can be divided into four levels:suitable construction area, relatively suitable construction area, general construction area and control construction area, the distribution and properties of each zone are obviously affected by the thickness of the various zone; compared with other cities, the construction suitability zones of sponge city construction in Tianjin are less affected by the topographic slope.
Based on the analysis of the geological factors influencing the construction of sponge city in Tianjin, We have established the evaluation index system of the geological suitability for the construction of sponge city in the south plain area of Tianjin; AHP method was used to assign the weight of evaluation index for the geological suitability of sponge city construction, than the comprehensive scoring method was used to score the influencing factors, and ARCGIS was used to carry out the weighted superposition of the two, finally realizing the geological suitability zoning of sponge city construction in Tianjin; combined with the overall score, distribution range and regional nature of each district, this paper gives the LID facilities type suitable for the construction of sponge cities in south Tianjin plain area. The results show that the geological suitability of sponge city construction in the central city of Tianjin(including four areas around the city) and the Binhai new area can be divided into four levels:suitable construction area, relatively suitable construction area, general construction area and control construction area, the distribution and properties of each zone are obviously affected by the thickness of the various zone; compared with other cities, the construction suitability zones of sponge city construction in Tianjin are less affected by the topographic slope.
2019, 27(s1): 9-16.
The development and utilization of underground space have become the tendency for city construction, and in such cases, urban geological condition is decisive in the development and utilization of underground space in safety and economy, when the development and utilization of urban underground space are restricted by the key geological factors. Based on the researching of regional geology, geological structure, seismogeology, groundwater and surface water, properties of special rock and soil, the adverse geological actions and geological disaster, the influencing grade of geological conditions to the development of urban underground space in Yueyang city are discussed. And then the suitability zoning of urban underground space had been catalogued to 4 parties such as perfectly suitable region, suitable region, poor adaptation region and inferior region. It can provide geological basis for the preliminary planning and decision making of the underground project in Yueyang city.
The development and utilization of underground space have become the tendency for city construction, and in such cases, urban geological condition is decisive in the development and utilization of underground space in safety and economy, when the development and utilization of urban underground space are restricted by the key geological factors. Based on the researching of regional geology, geological structure, seismogeology, groundwater and surface water, properties of special rock and soil, the adverse geological actions and geological disaster, the influencing grade of geological conditions to the development of urban underground space in Yueyang city are discussed. And then the suitability zoning of urban underground space had been catalogued to 4 parties such as perfectly suitable region, suitable region, poor adaptation region and inferior region. It can provide geological basis for the preliminary planning and decision making of the underground project in Yueyang city.
2019, 27(s1): 17-22.
A deep foundation pit in Nanjing is located on the lower bank of the Yangtze River. The site is a typical binary structure with widely distributed muddy silty soil, high pressure water level, and complex geological conditions of the foundation pit. The foundation pit is adjacent to a high-rise building. The excavation scope involves thick muddy silty soil, and the supporting structure is all buried in the muddy silty soil. The excavation sequence of the foundation pit is directly related to the safety of the foundation pit and surrounding buildings. Based on the condition of the deepest part of the foundation pit, the excavation sequence of the foundation pit is divided into 3 methods:I first excavation of the main tunnel and then excavation of the ramp; Ⅱ first excavation of the ramps and then excavation of the main tunnel; Ⅲ parallel excavation of the main tunnel and the ramp, using FLAC3D simulation software to analyse the deformation of the supporting of foundation pit and surrounding buildings under three excavation methods. And know that when first excavation of the main tunnel and then excavation of the ramp or first excavation of the ramps and then excavation of the main tunnel, the deformation and impacts on surrounding buildings and the supporting of foundation pit is minimal. This study provides experience for the excavation and design of deep and large foundation pits in deep muddy silty soil.
A deep foundation pit in Nanjing is located on the lower bank of the Yangtze River. The site is a typical binary structure with widely distributed muddy silty soil, high pressure water level, and complex geological conditions of the foundation pit. The foundation pit is adjacent to a high-rise building. The excavation scope involves thick muddy silty soil, and the supporting structure is all buried in the muddy silty soil. The excavation sequence of the foundation pit is directly related to the safety of the foundation pit and surrounding buildings. Based on the condition of the deepest part of the foundation pit, the excavation sequence of the foundation pit is divided into 3 methods:I first excavation of the main tunnel and then excavation of the ramp; Ⅱ first excavation of the ramps and then excavation of the main tunnel; Ⅲ parallel excavation of the main tunnel and the ramp, using FLAC3D simulation software to analyse the deformation of the supporting of foundation pit and surrounding buildings under three excavation methods. And know that when first excavation of the main tunnel and then excavation of the ramp or first excavation of the ramps and then excavation of the main tunnel, the deformation and impacts on surrounding buildings and the supporting of foundation pit is minimal. This study provides experience for the excavation and design of deep and large foundation pits in deep muddy silty soil.
2019, 27(s1): 23-30.
Single-layer lining is a very mature technology in Europe, which is developed continuously in the construction process of hard rock underground engineering based on Q system. Since the introduction of single-layer lining technology in the 1960s, China has adopted single-layer lining as permanent lining in more than a dozen projects, and achieved good results. However, due to the construction technology, materials, equipment and management, it has not been fully popularized. Based on the research project of single-layer lining of Xizhen Station of Qingdao Metro, this paper introduces the function and content of geological logging for tunnel construction, and expounds in detail the specific requirements, principles, key points and steps of drawing full-section geological sketch-map of single-layer lining. Finally, according to the results of geological logging and sketch maps, the six parameters of Q system are assigned and the corresponding Q values are calculated. According to(Q,De) in Q system supporting maps, the tunnel supporting parameters are preliminarily determined, The Unwedge program was used to analyze the stability of the wedge block with the main discontinuities combination before and after the support. and the final design parameters of single-layer lining support are determined by referring to geological conditions and local experience of similar projects in the past.
Single-layer lining is a very mature technology in Europe, which is developed continuously in the construction process of hard rock underground engineering based on Q system. Since the introduction of single-layer lining technology in the 1960s, China has adopted single-layer lining as permanent lining in more than a dozen projects, and achieved good results. However, due to the construction technology, materials, equipment and management, it has not been fully popularized. Based on the research project of single-layer lining of Xizhen Station of Qingdao Metro, this paper introduces the function and content of geological logging for tunnel construction, and expounds in detail the specific requirements, principles, key points and steps of drawing full-section geological sketch-map of single-layer lining. Finally, according to the results of geological logging and sketch maps, the six parameters of Q system are assigned and the corresponding Q values are calculated. According to(Q,De) in Q system supporting maps, the tunnel supporting parameters are preliminarily determined, The Unwedge program was used to analyze the stability of the wedge block with the main discontinuities combination before and after the support. and the final design parameters of single-layer lining support are determined by referring to geological conditions and local experience of similar projects in the past.
2019, 27(s1): 31-36.
A dynamic consolidation scheme of 5000~6000 m kN·m energy level is proposed for a riprap reclamation foundation of an electric power project in Guangdong province. The dynamic compaction tests with different energy levels are carried out, and the results of dynamic compaction foundation treatment are compared by means of pore water pressure detection, surface deformation observation around tamping points, heavy-duty dynamic penetration test, Rayleigh wave test, plate load test, and so on. The comprehensive test results show that the dynamic compaction method is better suited to the treatment of riprap reclaimed foundation, and the performance of the treated foundation is improved obviously. At the same time, the effective reinforcement depth and the bearing capacity of the foundation under different energy levels are also found out. It provides the scientific basis for the follow-up large area construction.
A dynamic consolidation scheme of 5000~6000 m kN·m energy level is proposed for a riprap reclamation foundation of an electric power project in Guangdong province. The dynamic compaction tests with different energy levels are carried out, and the results of dynamic compaction foundation treatment are compared by means of pore water pressure detection, surface deformation observation around tamping points, heavy-duty dynamic penetration test, Rayleigh wave test, plate load test, and so on. The comprehensive test results show that the dynamic compaction method is better suited to the treatment of riprap reclaimed foundation, and the performance of the treated foundation is improved obviously. At the same time, the effective reinforcement depth and the bearing capacity of the foundation under different energy levels are also found out. It provides the scientific basis for the follow-up large area construction.
2019, 27(s1): 37-45.
Considering on the monitoring problem of foundation pit settlement, four prediction models were proposed. Model 1 was a traditional grey Verhulst model. Model 2 was an optimized grey Verhulst model which used the reciprocal transformation and the optimization model without constraint to acquire the parameters of the background value and initial value. Model 3 was an optimized discrete grey Verhulst model that was built on the reciprocal transformation of the original data sequence by discretization method. Model 4 was an optimized discrete grey Verhulst model constructed through the metabolic method. The proposed models were used to predict the settlement of the foundation pit of a building in Longcheng Industrial Park in Shenzhen. The comparison between the calculated results and the measured results shows that the optimized gray discrete Verhulst model with the metabolic method has higher prediction accuracy and stability, and could better describe the settlement.
Considering on the monitoring problem of foundation pit settlement, four prediction models were proposed. Model 1 was a traditional grey Verhulst model. Model 2 was an optimized grey Verhulst model which used the reciprocal transformation and the optimization model without constraint to acquire the parameters of the background value and initial value. Model 3 was an optimized discrete grey Verhulst model that was built on the reciprocal transformation of the original data sequence by discretization method. Model 4 was an optimized discrete grey Verhulst model constructed through the metabolic method. The proposed models were used to predict the settlement of the foundation pit of a building in Longcheng Industrial Park in Shenzhen. The comparison between the calculated results and the measured results shows that the optimized gray discrete Verhulst model with the metabolic method has higher prediction accuracy and stability, and could better describe the settlement.
2019, 27(s1): 46-53.
This paper presents a numerical study on the dynamic effect on the mechanics behavior of subgrade near the high-rise residential community. Three-dimensional finite difference analysis based on Mohr-Coulomb criterion is adopted. The mechanics characteristics and failure mode under static and seismic conditions were discussed by FLAC3D. The numerical results showed that subgrade is safe under static and seismic conditions. Under the seismic, both horizontal acceleration and vertical acceleration have amplification effect along the elevation, especially the horizontal acceleration is amplified largely. The amplification effect at slope surface and slop body is different which indicates the air front effect. As the elevation increasing, the frequency component of the slope around its natural vibration frequency is significant amplified and other high frequency components were filtered. Ground motions of different amplitudes(PGA=0.15, 0.45, 0.62g) have different effect on dynamic response of acceleration. The subgrade slope under the horizontal seismic wave has amplification effect to input seismic waves, and the effect become extremely prominent around the crest of the slope. The subgrade slope under the vertical seismic wave behaves differently, the amplification effect enhances evidently near the crest of the inner slope. Geogrid reinforcement can greatly improve the seismic stability of the embankment.
This paper presents a numerical study on the dynamic effect on the mechanics behavior of subgrade near the high-rise residential community. Three-dimensional finite difference analysis based on Mohr-Coulomb criterion is adopted. The mechanics characteristics and failure mode under static and seismic conditions were discussed by FLAC3D. The numerical results showed that subgrade is safe under static and seismic conditions. Under the seismic, both horizontal acceleration and vertical acceleration have amplification effect along the elevation, especially the horizontal acceleration is amplified largely. The amplification effect at slope surface and slop body is different which indicates the air front effect. As the elevation increasing, the frequency component of the slope around its natural vibration frequency is significant amplified and other high frequency components were filtered. Ground motions of different amplitudes(PGA=0.15, 0.45, 0.62g) have different effect on dynamic response of acceleration. The subgrade slope under the horizontal seismic wave has amplification effect to input seismic waves, and the effect become extremely prominent around the crest of the slope. The subgrade slope under the vertical seismic wave behaves differently, the amplification effect enhances evidently near the crest of the inner slope. Geogrid reinforcement can greatly improve the seismic stability of the embankment.
2019, 27(s1): 54-59.
Generalized potential theory avoids the traditional concept of yield surface, thereby provides a new perspective in the study of constitutive models for geomaterials. The multiple potential surface model, which is based on the generalized potential theory, can conduct the numerical analysis of embankment dam with the same parameters as those of commonly used Duncan-Chang model as well as Shen's model, and exhibits fine versatility. In this paper, the numerical analysis of a typical embankment dam using the multiple potential surface model was conducted, and the comparison with Shen's model was made. To simulate the unsaturated properties of soils and their influence on the stress-strain and phreatic line in the dam, the simplified theory for unsaturated soil suggested by Shen Zhujiang was employed. Results showed that under the same condition, the displacement calculated by the multiple potential surface model was smaller than that calculated by Shen's model, thereby affecting the development of the phreatic line.
Generalized potential theory avoids the traditional concept of yield surface, thereby provides a new perspective in the study of constitutive models for geomaterials. The multiple potential surface model, which is based on the generalized potential theory, can conduct the numerical analysis of embankment dam with the same parameters as those of commonly used Duncan-Chang model as well as Shen's model, and exhibits fine versatility. In this paper, the numerical analysis of a typical embankment dam using the multiple potential surface model was conducted, and the comparison with Shen's model was made. To simulate the unsaturated properties of soils and their influence on the stress-strain and phreatic line in the dam, the simplified theory for unsaturated soil suggested by Shen Zhujiang was employed. Results showed that under the same condition, the displacement calculated by the multiple potential surface model was smaller than that calculated by Shen's model, thereby affecting the development of the phreatic line.
2019, 27(s1): 60-67.
Taking engineering examples as background, establishing a three-dimensional numerical analysis model to study the deformation characteristics of irregular reinforced earth retaining wall by changing the auxiliary reinforcement mode on the basis of single-stage vertical reinforced earth retaining wall with 90°corner by using numerical analysis software FLAC3D. The results show that:(1)Adding reinforcement can significantly reduce the deformation of the corner of reinforced earth retaining wall and alleviate the concentrated deformation effect of the top of the corner. (2)Adding half of the reinforcement in the upper part of the wall height can not control the corner deformation of the retaining wall as a whole, but it can also play a good role, and it is more economical. Specific schemes can be selected according to needs. (3)The variation of the spacing between the auxiliary reinforcement and the main reinforcement has little effect on the deformation of the corner. It can be flexibly adjusted in design and construction according to the actual situation. (4)The maximum tensile stress distribution of geogrid at corners presents an "X" shape, which is obviously different from the distribution of parallel walls at straight part, and the deformation is significantly greater than that at straight part. (5)The tension stress of the outer edge of geogrid is the largest at 6 m from the corner, which can be used for reference for specific projects, that is,to strengthen the deformation control of retaining wall around 6 m.
Taking engineering examples as background, establishing a three-dimensional numerical analysis model to study the deformation characteristics of irregular reinforced earth retaining wall by changing the auxiliary reinforcement mode on the basis of single-stage vertical reinforced earth retaining wall with 90°corner by using numerical analysis software FLAC3D. The results show that:(1)Adding reinforcement can significantly reduce the deformation of the corner of reinforced earth retaining wall and alleviate the concentrated deformation effect of the top of the corner. (2)Adding half of the reinforcement in the upper part of the wall height can not control the corner deformation of the retaining wall as a whole, but it can also play a good role, and it is more economical. Specific schemes can be selected according to needs. (3)The variation of the spacing between the auxiliary reinforcement and the main reinforcement has little effect on the deformation of the corner. It can be flexibly adjusted in design and construction according to the actual situation. (4)The maximum tensile stress distribution of geogrid at corners presents an "X" shape, which is obviously different from the distribution of parallel walls at straight part, and the deformation is significantly greater than that at straight part. (5)The tension stress of the outer edge of geogrid is the largest at 6 m from the corner, which can be used for reference for specific projects, that is,to strengthen the deformation control of retaining wall around 6 m.
2019, 27(s1): 68-73.
The mechanical properties of shallow loess are mainly affected by seasonal rainfall and drought climate, which shows that the loess has large subsidence and collapse after it meets water. The study on mechanical properties of shallow loess can provide some references for preventing and controlling geological hazards in loess area. In this paper, shallow loess in a certain area of Lanzhou is selected for direct shear test in laboratory, direct shear test under dry-wet cycling, unconfined compressive strength test and permeability test. The results show that at the same shear rate, the water content increases, the cohesion decreases and the internal friction angle changes little; at the same water content, the shear rate increases, the cohesion increases and the internal friction angle changes little. The cohesion of remolded loess decreases with the increase of wet and dry cycles, and the internal friction angle does not change much. The unconfined compressive strength of loess decreases with the increase of water content and the number of dry-wet cycles, and after more than four dry-wet cycles, the compressive strength of loess tends to be stable. The permeability coefficient of remolded loess increases with the number of dry-wet cycles and decreases with the increase of dry density.
The mechanical properties of shallow loess are mainly affected by seasonal rainfall and drought climate, which shows that the loess has large subsidence and collapse after it meets water. The study on mechanical properties of shallow loess can provide some references for preventing and controlling geological hazards in loess area. In this paper, shallow loess in a certain area of Lanzhou is selected for direct shear test in laboratory, direct shear test under dry-wet cycling, unconfined compressive strength test and permeability test. The results show that at the same shear rate, the water content increases, the cohesion decreases and the internal friction angle changes little; at the same water content, the shear rate increases, the cohesion increases and the internal friction angle changes little. The cohesion of remolded loess decreases with the increase of wet and dry cycles, and the internal friction angle does not change much. The unconfined compressive strength of loess decreases with the increase of water content and the number of dry-wet cycles, and after more than four dry-wet cycles, the compressive strength of loess tends to be stable. The permeability coefficient of remolded loess increases with the number of dry-wet cycles and decreases with the increase of dry density.
SEASONAL FROZEN TURFY SOIL SUBGRADE SETTLEMENT PREDICTION STUDY ON GREY AND BP NEURAL NETWORK THEORY
2019, 27(s1): 74-83.
With the development of highway and railway construction in northern China, expressways inevitably pass through the turfy soil area. Turfy soil in seasonal frozen area has high water content, organic matter and low decomposition degree etc, so that theoretical calculation cannot meet the precision requirements of practical engineering. Therefore, this paper firstly analyzes the particular settlement mechanism of turfy soil subgrade in seasonal frozen area, and then puts forward to the optimized grey settlement prediction model and the two-dimension double-layer BP neural network settlement prediction model. The two simulation models not only take the disturbance due to complicated engineering geological properties of turfy soil and seasonal freezing in northern China into account, but also introduce filling condition as one of engineering factors to deep learn subgrade settlement changes law. This paper takes the actual settlement monitoring data of seasonal turfy soil subgrade from jilin to yanji close to Changbai Mountain for instance, both the fitted and the predicted results of two models are comparatively analyzed which shows both of two models have high accuracy, but each has its own advantages and disadvantages. thus, this paper further summarizes the similarities and differences of two models in this kind of engineering, which in the meantime provides some reference for the application of the multi-factor prediction model to such turfy soil subgrade settlement prediction in northern China.
With the development of highway and railway construction in northern China, expressways inevitably pass through the turfy soil area. Turfy soil in seasonal frozen area has high water content, organic matter and low decomposition degree etc, so that theoretical calculation cannot meet the precision requirements of practical engineering. Therefore, this paper firstly analyzes the particular settlement mechanism of turfy soil subgrade in seasonal frozen area, and then puts forward to the optimized grey settlement prediction model and the two-dimension double-layer BP neural network settlement prediction model. The two simulation models not only take the disturbance due to complicated engineering geological properties of turfy soil and seasonal freezing in northern China into account, but also introduce filling condition as one of engineering factors to deep learn subgrade settlement changes law. This paper takes the actual settlement monitoring data of seasonal turfy soil subgrade from jilin to yanji close to Changbai Mountain for instance, both the fitted and the predicted results of two models are comparatively analyzed which shows both of two models have high accuracy, but each has its own advantages and disadvantages. thus, this paper further summarizes the similarities and differences of two models in this kind of engineering, which in the meantime provides some reference for the application of the multi-factor prediction model to such turfy soil subgrade settlement prediction in northern China.
2019, 27(s1): 84-88.
This paper studies the overall stability analysis method of the establishment of the corresponding reinforced embankment on the basis of Janbu Law, in light of the characteristics of thin soft foundation. Under certain assumed conditions, thin layer of soft foundation safety coefficient expression and the tangential force of expression are deduced in accordance with the principle of reinforced cushion action principle and through the stress analysis of reinforced material and the overall stability of the embankment limit equilibrium analysis of reinforced cushion. The overall stability and safety factor of reinforced embankment cushion based on Janbu Law are obtained through iteration. Then, Python language is adopted to program the overall stability evaluation method of reinforced embankment proposed in this paper. Combined with the calculation and analysis of practical cases, the feasibility of the established stability analysis method is verified.
This paper studies the overall stability analysis method of the establishment of the corresponding reinforced embankment on the basis of Janbu Law, in light of the characteristics of thin soft foundation. Under certain assumed conditions, thin layer of soft foundation safety coefficient expression and the tangential force of expression are deduced in accordance with the principle of reinforced cushion action principle and through the stress analysis of reinforced material and the overall stability of the embankment limit equilibrium analysis of reinforced cushion. The overall stability and safety factor of reinforced embankment cushion based on Janbu Law are obtained through iteration. Then, Python language is adopted to program the overall stability evaluation method of reinforced embankment proposed in this paper. Combined with the calculation and analysis of practical cases, the feasibility of the established stability analysis method is verified.
2019, 27(s1): 89-94.
There are abundant wind energy resources in Northwest China, but the cost of wind farm construction increases due to the treatment of loess collapsible under overburden pressure in this area. Exploring the optimization scheme of WTG foundation in collapsible loess area has great significance to the development of wind energy. In this paper, the infiltration process of rain fall in loess is simulated using finite element method with unsaturated soil, and the range and location of the water-resisting layer are determined using the simulation results. Then the replacement thickness is determined according to different collapsibility coefficients to meet the requirements of bearing capacity and collapsibility. The replacement schemes under different collapsibility coefficients are obtained. The optimization scheme can both ensure safety and save the cost of wind farm. Since the Ningxia wind farm has been built three years, the test results show that the optimized scheme is safe and reliable.
There are abundant wind energy resources in Northwest China, but the cost of wind farm construction increases due to the treatment of loess collapsible under overburden pressure in this area. Exploring the optimization scheme of WTG foundation in collapsible loess area has great significance to the development of wind energy. In this paper, the infiltration process of rain fall in loess is simulated using finite element method with unsaturated soil, and the range and location of the water-resisting layer are determined using the simulation results. Then the replacement thickness is determined according to different collapsibility coefficients to meet the requirements of bearing capacity and collapsibility. The replacement schemes under different collapsibility coefficients are obtained. The optimization scheme can both ensure safety and save the cost of wind farm. Since the Ningxia wind farm has been built three years, the test results show that the optimized scheme is safe and reliable.
2019, 27(s1): 95-103.
Geological conditions changes frequently in the composite strata contained various soft and hard rocks. The serious wear of disc cutter severely restricts the construction efficiency. In order to explore the wear resistant measures and predict the wear extent and cutting life of the disc cutter of earth pressure balanced(EPB)shield TBM in composite strata, the statistical regression method was used to analyze the wear extent and replacement process of disc cutter in the excavation interval of ZDK30+433.76to ZDK31+150.61 of the Guangzhou Metro Line 18. Based on the actual wear extent of disc cutter and the tunneling parameters of EPB shield TBM,the wear coefficient K suitable for the composite strata contained various soft and hard rocks is obtained. Then, the wear extent and the cutting life of disc cutter of EPB shield TBM in the composite strata are predicted and analyzed according to the wear coefficient K and the corresponding disc cutter wear model. Subsequently, measures such as the improvement of disc cutter, the optimization of construction parameters, the majorization of management and the amelioration of residue are proposed to reduce the wear extent of disc cutter. Finally, the optimization of the tunneling parameters of the EPB shield TBM this project is carried out, and the recommended rotation speed for EPB shield TBM under-passing the Shawan waterway is proposed. The study provides engineering experience and theoretical basis for the prediction of disc cutter wear and the choice of tool change opportunity in Guangzhou Metro Line 18 and similar tunnels project in composite strata.
Geological conditions changes frequently in the composite strata contained various soft and hard rocks. The serious wear of disc cutter severely restricts the construction efficiency. In order to explore the wear resistant measures and predict the wear extent and cutting life of the disc cutter of earth pressure balanced(EPB)shield TBM in composite strata, the statistical regression method was used to analyze the wear extent and replacement process of disc cutter in the excavation interval of ZDK30+433.76to ZDK31+150.61 of the Guangzhou Metro Line 18. Based on the actual wear extent of disc cutter and the tunneling parameters of EPB shield TBM,the wear coefficient K suitable for the composite strata contained various soft and hard rocks is obtained. Then, the wear extent and the cutting life of disc cutter of EPB shield TBM in the composite strata are predicted and analyzed according to the wear coefficient K and the corresponding disc cutter wear model. Subsequently, measures such as the improvement of disc cutter, the optimization of construction parameters, the majorization of management and the amelioration of residue are proposed to reduce the wear extent of disc cutter. Finally, the optimization of the tunneling parameters of the EPB shield TBM this project is carried out, and the recommended rotation speed for EPB shield TBM under-passing the Shawan waterway is proposed. The study provides engineering experience and theoretical basis for the prediction of disc cutter wear and the choice of tool change opportunity in Guangzhou Metro Line 18 and similar tunnels project in composite strata.
2019, 27(s1): 104-109.
In great earthquakes, active faulting often leads to the rupture in overlying soil and causes significant damages to constructions including tunnels. We simulated the failure process of soil-tunnel system under the active fault movement with a dip angle of 60ånd explored the tunnel response under fault movement. Results indicate that for footwall tunnels, the tunnellocating near the rupture suffers from great moment and shear force. When the tunnel keeps a certain distance from the fault, the moment and shear force decrease rapidly. In order to ensure its safety, the footwall tunnel needs to keep a safe distance of more than 30 m from the fault. For hanging wall tunnels, they bear tiny moment and shear force, but great displacement will be generated under fault movement. Further studies show that soil property including elastic modulus and dilation angle have significant effects on tunnel response. In stiffer soil, a smaller fault dislocation is required for the rupture to reach the ground surface and the tunnel bears smaller peak loads. Greater soil dilation angle leads to a smaller rupture dip angle and the tunnel suffers from larger peak loads.
In great earthquakes, active faulting often leads to the rupture in overlying soil and causes significant damages to constructions including tunnels. We simulated the failure process of soil-tunnel system under the active fault movement with a dip angle of 60ånd explored the tunnel response under fault movement. Results indicate that for footwall tunnels, the tunnellocating near the rupture suffers from great moment and shear force. When the tunnel keeps a certain distance from the fault, the moment and shear force decrease rapidly. In order to ensure its safety, the footwall tunnel needs to keep a safe distance of more than 30 m from the fault. For hanging wall tunnels, they bear tiny moment and shear force, but great displacement will be generated under fault movement. Further studies show that soil property including elastic modulus and dilation angle have significant effects on tunnel response. In stiffer soil, a smaller fault dislocation is required for the rupture to reach the ground surface and the tunnel bears smaller peak loads. Greater soil dilation angle leads to a smaller rupture dip angle and the tunnel suffers from larger peak loads.
2019, 27(s1): 110-120.
Frequent mountain hazards are one of the most critical factors for the successful construction of Sichuan-Tibet railway. Based on remote sensing interpretation, field investigation and mathematical statistics, we analyzed and summarized the types, characteristics and spatial distribution law of the landslides and collapses along Sichuan-Tibet railway. We identified 747 hazards along the railway, including 310 collapses, 413 landslides and 24 sand-sliding slopes. The average distribution line density of the hazards is 0.40 point/km, Baiyu to Jiangda section has the biggest line density(1.29 place/km). 258 mountain hazards have a potential threat and influence on the proposed railway engineering, including 156 landslides, 91 collapses and 11 sand-sliding slopes. In addition, we analyzed the relationship between the hazards and their impact factors. We found that the distribution of the hazards is comprehensively controlled and influenced by lithology, structure, geomorphology, river system and other factors, and has the characteristics of uneven and clustered distribution. On this basis, the development degree of landslides and collapses along Sichuan-Tibet railways was divided into 5 levels and 14 segments combining the development degree index of the hazards with the subsection standard. The Baiyu to Jiangda section, Bangda to Basu section are extremely strong development sections, Tianquan to Xindu section, Guxiang to Layue section and langxian to Jiachasection are strong development sections for the hazards. This study can provide an important scientific theory and decision-making support for line selection and safe operation of Sichuan-Tibet railway.
Frequent mountain hazards are one of the most critical factors for the successful construction of Sichuan-Tibet railway. Based on remote sensing interpretation, field investigation and mathematical statistics, we analyzed and summarized the types, characteristics and spatial distribution law of the landslides and collapses along Sichuan-Tibet railway. We identified 747 hazards along the railway, including 310 collapses, 413 landslides and 24 sand-sliding slopes. The average distribution line density of the hazards is 0.40 point/km, Baiyu to Jiangda section has the biggest line density(1.29 place/km). 258 mountain hazards have a potential threat and influence on the proposed railway engineering, including 156 landslides, 91 collapses and 11 sand-sliding slopes. In addition, we analyzed the relationship between the hazards and their impact factors. We found that the distribution of the hazards is comprehensively controlled and influenced by lithology, structure, geomorphology, river system and other factors, and has the characteristics of uneven and clustered distribution. On this basis, the development degree of landslides and collapses along Sichuan-Tibet railways was divided into 5 levels and 14 segments combining the development degree index of the hazards with the subsection standard. The Baiyu to Jiangda section, Bangda to Basu section are extremely strong development sections, Tianquan to Xindu section, Guxiang to Layue section and langxian to Jiachasection are strong development sections for the hazards. This study can provide an important scientific theory and decision-making support for line selection and safe operation of Sichuan-Tibet railway.
2019, 27(s1): 121-124.
Landslides happen frequently in Ruili City, In order to reveal the causes of landslide geological hazards in Ruili City, based on the investigation and statistical results, the temporal and spatial distribution characteristics of landslides are analyzed. Based on the factors influencing landslide occurrence, such as landform, geological structure, type of rock and soil structure, rainfall and human engineering activities, the main component(R-type factor) analysis and stepwise regression analysis are used to obtain the rock and soil types. Type I is the main controlling factor affecting landslide formation, and rainfall and human engineering activities are the main triggering factors.
Landslides happen frequently in Ruili City, In order to reveal the causes of landslide geological hazards in Ruili City, based on the investigation and statistical results, the temporal and spatial distribution characteristics of landslides are analyzed. Based on the factors influencing landslide occurrence, such as landform, geological structure, type of rock and soil structure, rainfall and human engineering activities, the main component(R-type factor) analysis and stepwise regression analysis are used to obtain the rock and soil types. Type I is the main controlling factor affecting landslide formation, and rainfall and human engineering activities are the main triggering factors.
2019, 27(s1): 125-130.
Since the reform and opening up, with the rapid development of the country's economic construction, more and more engineering projects are located in mountainous areas with complex terrain. Due to the restrictions of site conditions, mountains must be excavated, resulting in geological disasters such as landslides and collapses, which have caused serious construction projects. threat. Loess is mainly distributed in the middle reaches of the yellow river, accounting for 6.3% of the total land area. It forms landforms such as loess beams, loess platforms, et al.,and loess is also prone to geological hazards such as landslides and collapses. This paper discusses the characteristics, influencing factors, stability analysis, choice of management plan, management effect and deformation monitoring of the landslide of the ash dam in a power plant which has recently been investigated, designed and constructed. In order to provide the basis for the management design and construction of similar projects.
Since the reform and opening up, with the rapid development of the country's economic construction, more and more engineering projects are located in mountainous areas with complex terrain. Due to the restrictions of site conditions, mountains must be excavated, resulting in geological disasters such as landslides and collapses, which have caused serious construction projects. threat. Loess is mainly distributed in the middle reaches of the yellow river, accounting for 6.3% of the total land area. It forms landforms such as loess beams, loess platforms, et al.,and loess is also prone to geological hazards such as landslides and collapses. This paper discusses the characteristics, influencing factors, stability analysis, choice of management plan, management effect and deformation monitoring of the landslide of the ash dam in a power plant which has recently been investigated, designed and constructed. In order to provide the basis for the management design and construction of similar projects.
2019, 27(s1): 131-137.
Transmission line is one of the most important lifelines. It often crosses a long transmission distance and covers a wide range. Along the transmission line the environmet significantly varies; the geomorphological and geological conditions are complext, w,which makes the transmission line is threaten by geological hazards. Especially in recent years, affected by extreme climate, the geological hazards along the important transmission lines appear to be of high-frequency. The situation of hazards prevention and control is severe. In order to guarantee the safe operation of massive power grid in extereme environment, the geological hazards risk assement of important transmission lines is urgently needed. In this paper the selected indices include:slope, aspect, slope length, curvature, cutting depth, road buffering, river buffering, surface roughness, surface deformation, surface moisture content etc. By using the contribution weight model to evaluate the geological hazard of the typical transmission channel named Lu Mao line. The results show that,(1)the most contribution rate of geological hazards is aspect, then slope, river buffering, road buffering and so on. (2)The whole transmission channel is mainly in the lower hazard area and the moderate hazard area, and the area accounts for 58.22% of the whole area. (3)From the low risk area to the high hazard area the disaster distribution density gradually increases, from no disaster to 0.536/km2. And the hazard degree of each pole tower was analyzed and evaluated.
Transmission line is one of the most important lifelines. It often crosses a long transmission distance and covers a wide range. Along the transmission line the environmet significantly varies; the geomorphological and geological conditions are complext, w,which makes the transmission line is threaten by geological hazards. Especially in recent years, affected by extreme climate, the geological hazards along the important transmission lines appear to be of high-frequency. The situation of hazards prevention and control is severe. In order to guarantee the safe operation of massive power grid in extereme environment, the geological hazards risk assement of important transmission lines is urgently needed. In this paper the selected indices include:slope, aspect, slope length, curvature, cutting depth, road buffering, river buffering, surface roughness, surface deformation, surface moisture content etc. By using the contribution weight model to evaluate the geological hazard of the typical transmission channel named Lu Mao line. The results show that,(1)the most contribution rate of geological hazards is aspect, then slope, river buffering, road buffering and so on. (2)The whole transmission channel is mainly in the lower hazard area and the moderate hazard area, and the area accounts for 58.22% of the whole area. (3)From the low risk area to the high hazard area the disaster distribution density gradually increases, from no disaster to 0.536/km2. And the hazard degree of each pole tower was analyzed and evaluated.
2019, 27(s1): 138-143.
The K85 slope is a typical high cutting slope in the mountain of Fujian province, which is located in an expressway of Fujian province. During the slope treatment, there appeared cracking deformation and partially collapse, and formed a landslide disaster. The landslide affected the smooth opening of the line. So, for the similar slopes, it is great significance to study the deformation mechanism of this slope. In this paper, by analyzing the geological environment of the slope and the deformation of the slope excavation, the deformation and failure mechanism is described. It indicates that the deformation and failure mode is that the overlying weathered rock mass along the underlying rock surface caused the sliding deformation and damage. It uses finite element numerical simulation to analyze the steady-state of design schemes and actual construction conditions. And combining with on-site monitoring results, it confirms the deformation mechanism of these slopes. Meanwhile, it analyzes the risk prevention and control nodes about the treatment process in this kind of slope. Finally, the slope prevention and reinforcement scheme is optimized for the instability landslide. And, it is reasonable and feasible to verify the scheme by numerical simulation and new monitoring results.
The K85 slope is a typical high cutting slope in the mountain of Fujian province, which is located in an expressway of Fujian province. During the slope treatment, there appeared cracking deformation and partially collapse, and formed a landslide disaster. The landslide affected the smooth opening of the line. So, for the similar slopes, it is great significance to study the deformation mechanism of this slope. In this paper, by analyzing the geological environment of the slope and the deformation of the slope excavation, the deformation and failure mechanism is described. It indicates that the deformation and failure mode is that the overlying weathered rock mass along the underlying rock surface caused the sliding deformation and damage. It uses finite element numerical simulation to analyze the steady-state of design schemes and actual construction conditions. And combining with on-site monitoring results, it confirms the deformation mechanism of these slopes. Meanwhile, it analyzes the risk prevention and control nodes about the treatment process in this kind of slope. Finally, the slope prevention and reinforcement scheme is optimized for the instability landslide. And, it is reasonable and feasible to verify the scheme by numerical simulation and new monitoring results.
2019, 27(s1): 144-148.
In this study, a detailed geological investigation was carried out on the rockfall event at the back edge of Laoshucuo region in Wu Gorge, and the numerical back analysis calculation and parameter susceptivity analysis were carried out on movement characteristics of the rockfall event. Based on the back analysis and field investigation of the rockfall event, it could be seen that the process of rockfall movement involved a free fall-impact slope(about 550 m altitude),rolling along the slope, Secondary impact slope(about 400 m altitude) and rolling along the slope. The energy reduction of the rockfall was mainly affected by the normal velocity loss of it when impacting on the slope. Considering that the state of slope cover being affected by various factors in nature, a susceptivity analysis of the normal recovery coefficient Rn,which represents the normal velocity loss of rockfall, was carried out in this study. It could be seen that the movement mode of the rockfall event in the final stage would be changed from rolling motion along the slope to bouncing motion on the slope with the increase of the normal recovery coefficient Rn. The speed of the rockfall entering the water of Changjiang River would increase significantly, which would cause a great impact on the water near entry point and affected the safe navigation of nearby vessels. Therefore, the actual and extreme conditions of the slope cover should be taken into account when preventing and evaluating the rockfall disaster at the back edge of the high steep slope in the study area in the future.
In this study, a detailed geological investigation was carried out on the rockfall event at the back edge of Laoshucuo region in Wu Gorge, and the numerical back analysis calculation and parameter susceptivity analysis were carried out on movement characteristics of the rockfall event. Based on the back analysis and field investigation of the rockfall event, it could be seen that the process of rockfall movement involved a free fall-impact slope(about 550 m altitude),rolling along the slope, Secondary impact slope(about 400 m altitude) and rolling along the slope. The energy reduction of the rockfall was mainly affected by the normal velocity loss of it when impacting on the slope. Considering that the state of slope cover being affected by various factors in nature, a susceptivity analysis of the normal recovery coefficient Rn,which represents the normal velocity loss of rockfall, was carried out in this study. It could be seen that the movement mode of the rockfall event in the final stage would be changed from rolling motion along the slope to bouncing motion on the slope with the increase of the normal recovery coefficient Rn. The speed of the rockfall entering the water of Changjiang River would increase significantly, which would cause a great impact on the water near entry point and affected the safe navigation of nearby vessels. Therefore, the actual and extreme conditions of the slope cover should be taken into account when preventing and evaluating the rockfall disaster at the back edge of the high steep slope in the study area in the future.
2019, 27(s1): 149-156.
Siltized intercalation is a typical weak structural plane, which often induces all kinds of engineering geological problems, such as slope instability, dam foundation instability and surrounding rock deformations of underground caverns. Therefore, studying the geological characteristics and the evolution progress of siltized intercalation and finding out the influence of siltized intercalation on slope stability is of great importance. This paper reviewed the formation mechanism, classification, spatial distribution, mechanical properties, geological characteristics and sliding stability of siltized intercalation in China. In general, the following main conclusions are obtained. There are three kinds of formation modes of siltized intercalation and interlayer dislocation is the most common formation model. The study of the spatial distribution of siltized intercalation mainly focuses on qualitative description and regular summary. Siltized intercalation is a visco-elastic-plastic system, the shear creep properties of siltized intercalation well studied. Finally, this paper also puts forward the key directions of the studies about the issues. They include the argilization process of weak interlayer, the three-dimensional spatial distribution and visualization of the siltized intercalation, shear creep theoretical model for siltized intercalation, the meso-damage and failure process, stress relaxation properties and the dynamic properties of siltized intercalation, the mechanical properties of composite rock mass and the interface between siltized intercalation and surrounding rock, the extensive and in-depth exploration of the effects of siltized intercalation on slope stability.
Siltized intercalation is a typical weak structural plane, which often induces all kinds of engineering geological problems, such as slope instability, dam foundation instability and surrounding rock deformations of underground caverns. Therefore, studying the geological characteristics and the evolution progress of siltized intercalation and finding out the influence of siltized intercalation on slope stability is of great importance. This paper reviewed the formation mechanism, classification, spatial distribution, mechanical properties, geological characteristics and sliding stability of siltized intercalation in China. In general, the following main conclusions are obtained. There are three kinds of formation modes of siltized intercalation and interlayer dislocation is the most common formation model. The study of the spatial distribution of siltized intercalation mainly focuses on qualitative description and regular summary. Siltized intercalation is a visco-elastic-plastic system, the shear creep properties of siltized intercalation well studied. Finally, this paper also puts forward the key directions of the studies about the issues. They include the argilization process of weak interlayer, the three-dimensional spatial distribution and visualization of the siltized intercalation, shear creep theoretical model for siltized intercalation, the meso-damage and failure process, stress relaxation properties and the dynamic properties of siltized intercalation, the mechanical properties of composite rock mass and the interface between siltized intercalation and surrounding rock, the extensive and in-depth exploration of the effects of siltized intercalation on slope stability.
2019, 27(s1): 157-163.
In the early morning of 24 June 2017,a landslide occurred in Xinmo village where located in the Wenchuan earthquake stricken zone raised great concerns in China and worldwide, because the landslide killed more than 80 people, damaged many houses, highways and facilities, and the volume is up to 8×106 m3. The preliminary research indicated that 1)historical earthquake seriously influenced the stability of the Xinmo landslide and generated several cracks near the ridge; 2)the slow-moving landslide cannot been detected in time due to tough geological condition and the limitation of observation equipment; and 3)a catastrophic landslide occurred without any prevention and mitigation measurements. Rainfall is main factor to trigger landslides except earthquake factor in the earthquake stricken zone. Furthermore, the Xinmo landslide was in a rainy weather in a rather long period before its occurrence. In this study, we aim to analyze the influence of rainfall on the Xinmo landslide by analyzing the rainfall characteristics in terms of yearly rainfall, monthly rainfall, daily rainfall and hourly rainfall. The rainfall data is obtained from the three rain-gage stations near the landslide. The results demonstrate that rainy weather in a long period before the landslide occurrence is the main reason to trigger the landslide totally failure. In particular, a rapid increased daily rainfall in April 9 accelerated the moving speed. To some extent, the landslide behaved some hysteresis on a larger daily rainfall in May 11 and June 14. In addition, a critical rainfall per hour and accumulative rainfall may be not adjusted to evaluate the slow-moving landslide. Accumulative effect of prolonged and low-intensity rainfall on slow-moving landslide cannot be neglect.
In the early morning of 24 June 2017,a landslide occurred in Xinmo village where located in the Wenchuan earthquake stricken zone raised great concerns in China and worldwide, because the landslide killed more than 80 people, damaged many houses, highways and facilities, and the volume is up to 8×106 m3. The preliminary research indicated that 1)historical earthquake seriously influenced the stability of the Xinmo landslide and generated several cracks near the ridge; 2)the slow-moving landslide cannot been detected in time due to tough geological condition and the limitation of observation equipment; and 3)a catastrophic landslide occurred without any prevention and mitigation measurements. Rainfall is main factor to trigger landslides except earthquake factor in the earthquake stricken zone. Furthermore, the Xinmo landslide was in a rainy weather in a rather long period before its occurrence. In this study, we aim to analyze the influence of rainfall on the Xinmo landslide by analyzing the rainfall characteristics in terms of yearly rainfall, monthly rainfall, daily rainfall and hourly rainfall. The rainfall data is obtained from the three rain-gage stations near the landslide. The results demonstrate that rainy weather in a long period before the landslide occurrence is the main reason to trigger the landslide totally failure. In particular, a rapid increased daily rainfall in April 9 accelerated the moving speed. To some extent, the landslide behaved some hysteresis on a larger daily rainfall in May 11 and June 14. In addition, a critical rainfall per hour and accumulative rainfall may be not adjusted to evaluate the slow-moving landslide. Accumulative effect of prolonged and low-intensity rainfall on slow-moving landslide cannot be neglect.
2019, 27(s1): 164-171.
Rain-induced landslide is a common geological hazard. The consequence of landslide hazard is closely related to its travel distance. The prediction of rain-induced landslide horizontal travel distance is the basis of quantitative risk assessment. This paper built a database through collecting 309 cases of rain-induced landslides systematically. According to the database, we statistically analyzed the horizontal travel distance, volume, vertical travel distance, initial slope gradient and aspect ratio. Then we developed a calibration method of rain-induced landslides travel distance empirical model considering both confined and unconfined landslides. The proposed method could not only get the prediction of horizontal travel distance, but also the model error and confidence interval. Single factor analysis shows that the correlation of vertical travel distance with horizontal travel distance is highest, following are volume, aspect ratio and initial slope gradient. Stepwise regression analysis shows that the prediction model of rain-induced landslides based on the vertical travel distance, volume and aspect ratio is the fittest.
Rain-induced landslide is a common geological hazard. The consequence of landslide hazard is closely related to its travel distance. The prediction of rain-induced landslide horizontal travel distance is the basis of quantitative risk assessment. This paper built a database through collecting 309 cases of rain-induced landslides systematically. According to the database, we statistically analyzed the horizontal travel distance, volume, vertical travel distance, initial slope gradient and aspect ratio. Then we developed a calibration method of rain-induced landslides travel distance empirical model considering both confined and unconfined landslides. The proposed method could not only get the prediction of horizontal travel distance, but also the model error and confidence interval. Single factor analysis shows that the correlation of vertical travel distance with horizontal travel distance is highest, following are volume, aspect ratio and initial slope gradient. Stepwise regression analysis shows that the prediction model of rain-induced landslides based on the vertical travel distance, volume and aspect ratio is the fittest.
2019, 27(s1): 172-178.
The progressive failure of landslide is a process from quantitative change to qualitative change. It usually starts from the foot of the slope and continues to destroy along a weak surface until a through sliding zone is formed. In order to study the influence of peak strength and residual strength on landslide instability, a strain softening model is adopted for sliding zone soil. Firstly, we use two-dimensional examples to illustrate the variation of sliding surface morphology, plastic zone and displacement of landslide, and invert the progressive failure process of landslide in two-dimensional space. Then we divide the instability process of the landslide into three stages:the creeping stage, the pressing stage and the sliding stage according to the displacement change. Based on the theory of slip-soil soil strain softening, the author studied the progressive failure process and failure law of landslide in three-dimensional space. The results show that in the three-dimensional space, the landslide first forms a plastic zone at the foot of the slope and the perimeter of the landslide. After that, the plastic zone increases along the perimeter of the landslide and forms a penetrating plastic zone. Comparing the two-dimensional and three-dimensional examples, it shows that the three-dimensional strain softening model of sliding zone soil is more realistic to reflect the whole process of progressive failure of landslide. Therefore, the strain softening model of sliding zone soil can truly reflect the progressive failure process of slope, which provides a theoretical basis for the early warning and monitoring of landslide.
The progressive failure of landslide is a process from quantitative change to qualitative change. It usually starts from the foot of the slope and continues to destroy along a weak surface until a through sliding zone is formed. In order to study the influence of peak strength and residual strength on landslide instability, a strain softening model is adopted for sliding zone soil. Firstly, we use two-dimensional examples to illustrate the variation of sliding surface morphology, plastic zone and displacement of landslide, and invert the progressive failure process of landslide in two-dimensional space. Then we divide the instability process of the landslide into three stages:the creeping stage, the pressing stage and the sliding stage according to the displacement change. Based on the theory of slip-soil soil strain softening, the author studied the progressive failure process and failure law of landslide in three-dimensional space. The results show that in the three-dimensional space, the landslide first forms a plastic zone at the foot of the slope and the perimeter of the landslide. After that, the plastic zone increases along the perimeter of the landslide and forms a penetrating plastic zone. Comparing the two-dimensional and three-dimensional examples, it shows that the three-dimensional strain softening model of sliding zone soil is more realistic to reflect the whole process of progressive failure of landslide. Therefore, the strain softening model of sliding zone soil can truly reflect the progressive failure process of slope, which provides a theoretical basis for the early warning and monitoring of landslide.
2019, 27(s1): 179-184.
In recent years, in the process of urban construction in Wuxi, geological hazards caused by covered karst have become more and more problematic. In this paper, based on the covered karst in the foundation of a section of Wuxi Metro, the karst development in the site is detected by using the cross-hole seismic CT technique. It is found that:(1)there are many karst caves in the site, the scale is generally small, and the buried depth of the caves varies greatly; (2)The karst caves in the site often penetrate with the Quaternary strata, and the connectivity and water-richness of the karst caves are better between karst caves. The roof rockmass of karst caves has low strength and poor stability, which has a great impact on engineering construction; (3)According to the shape, development position, filling state and filling type of caves, this paper divides the caves into five types. In view of these five different types of caves, combined with the engineering geological conditions of the site, the geological disasters are studied and analysed, and corresponding prevention and control measures are given. This study has certain reference and guiding significance for the construction design of the proposed subway tunnel.
In recent years, in the process of urban construction in Wuxi, geological hazards caused by covered karst have become more and more problematic. In this paper, based on the covered karst in the foundation of a section of Wuxi Metro, the karst development in the site is detected by using the cross-hole seismic CT technique. It is found that:(1)there are many karst caves in the site, the scale is generally small, and the buried depth of the caves varies greatly; (2)The karst caves in the site often penetrate with the Quaternary strata, and the connectivity and water-richness of the karst caves are better between karst caves. The roof rockmass of karst caves has low strength and poor stability, which has a great impact on engineering construction; (3)According to the shape, development position, filling state and filling type of caves, this paper divides the caves into five types. In view of these five different types of caves, combined with the engineering geological conditions of the site, the geological disasters are studied and analysed, and corresponding prevention and control measures are given. This study has certain reference and guiding significance for the construction design of the proposed subway tunnel.
2019, 27(s1): 185-192.
On December 16, 2018, at 12:46 am, a magnitude MS5.7 earthquake occurred in Xingwen County, Sichuan Province. The quake triggered a lot of landslides. Based on remote sensing images before and after the earthquake and the GIS platform, this study produced a distribution map of the earthquake-triggered landslide in the Ⅵ-Ⅶ intensity area by visual interpretation method, and analyzed the relationship between these landslides and several environmental factors such as elevation, slope, slope aspect, and slope curvature. The results show that at least 288 landslides were triggered by the earthquake, with a total area of 0.49 km2 and an average area of 1701 m2. Most of these landslides were small scale, while the largest reaching 51, 745 m2 and the smallest 111 m2. Most of the landslide developed in the areas of 700~1000 m in elevation, 5°~15°of slope angle, slope aspect between 180ånd 240°, 10 km range from the epicenter, and underlying of conglomerate, limestone and shale rock. This study provides a basis for further study on the spatial distribution, mechanism, risk assessment and prediction of seismic landslides.
On December 16, 2018, at 12:46 am, a magnitude MS5.7 earthquake occurred in Xingwen County, Sichuan Province. The quake triggered a lot of landslides. Based on remote sensing images before and after the earthquake and the GIS platform, this study produced a distribution map of the earthquake-triggered landslide in the Ⅵ-Ⅶ intensity area by visual interpretation method, and analyzed the relationship between these landslides and several environmental factors such as elevation, slope, slope aspect, and slope curvature. The results show that at least 288 landslides were triggered by the earthquake, with a total area of 0.49 km2 and an average area of 1701 m2. Most of these landslides were small scale, while the largest reaching 51, 745 m2 and the smallest 111 m2. Most of the landslide developed in the areas of 700~1000 m in elevation, 5°~15°of slope angle, slope aspect between 180ånd 240°, 10 km range from the epicenter, and underlying of conglomerate, limestone and shale rock. This study provides a basis for further study on the spatial distribution, mechanism, risk assessment and prediction of seismic landslides.
2019, 27(s1): 193-199.
It is thought that the internal friction angle of soil remains unchanged in traditional calculation methods for landslides. In fact, the internal friction angle of soil changes with slope sliding. We analyzed the process of landslides in consideration of the change of the internal friction angle of soil by the material point method. In the material point method, material points with regional information discretizes the slope body. It abandons deformed grids after a computational time step. New grids are employed in the next step. For the example in this paper, since the inertia parameter was small, the results in consideration of the change of the internal friction angle of soil are close to those with a fixed value of lower limit parameter. we further compared the influence of different bounds of friction coefficient on the process of landslides. The shape of the landslide will be flatter with larger sliding distance if the bound of friction coefficient being smaller.
It is thought that the internal friction angle of soil remains unchanged in traditional calculation methods for landslides. In fact, the internal friction angle of soil changes with slope sliding. We analyzed the process of landslides in consideration of the change of the internal friction angle of soil by the material point method. In the material point method, material points with regional information discretizes the slope body. It abandons deformed grids after a computational time step. New grids are employed in the next step. For the example in this paper, since the inertia parameter was small, the results in consideration of the change of the internal friction angle of soil are close to those with a fixed value of lower limit parameter. we further compared the influence of different bounds of friction coefficient on the process of landslides. The shape of the landslide will be flatter with larger sliding distance if the bound of friction coefficient being smaller.
2019, 27(s1): 200-206.
Rainfall is one of the most active external factors inducing landslides in nature. The reduction of landslide stability by rainfall infiltration is affected by rainfall intensity, rainfall duration, permeability of sliding body, runoff coefficient and lateral recharge, et al. However, there is a lack of lucubrating on the impact of rainfall infiltration on landslide stability in general projects. The researches show thatthe landslide of gravel soil landslide is mainly caused by the displacement of sliding body, the sliding state, the inconsistent play of friction stress on the sliding surface, the continuous development of plastic strain and the inconsistent development, and rainfall infiltration induces landslide mainly by changing the original stress and strain state of rock and soil mass. In landslide prevention and control engineering, shear strength, sliding weight degree, pore water pressure and seepage pressure of sliding zone soil are often taken as important parameters for slope stability analysis and engineering design of prevention and control, while the variation law of stress and strain of landslide rock and soil mass in the process of rainfall is seldom considered. In this paper, based on the constitutive model of gravel soil and the law of soil stress and strain change during rainfall infiltration, numerical simulation method is adopted to analyze the stability of a certain gravel soil landslide by considering factors such as permeability coefficient, runoff coefficient and infiltration intensity, then reveal the distribution of pore pressure and stress in the gravel soil landslide under the influence of rainfall infiltration combined with the observation of the landslide, as to provide theoretical basis for prevention and control ofthe landslide.
Rainfall is one of the most active external factors inducing landslides in nature. The reduction of landslide stability by rainfall infiltration is affected by rainfall intensity, rainfall duration, permeability of sliding body, runoff coefficient and lateral recharge, et al. However, there is a lack of lucubrating on the impact of rainfall infiltration on landslide stability in general projects. The researches show thatthe landslide of gravel soil landslide is mainly caused by the displacement of sliding body, the sliding state, the inconsistent play of friction stress on the sliding surface, the continuous development of plastic strain and the inconsistent development, and rainfall infiltration induces landslide mainly by changing the original stress and strain state of rock and soil mass. In landslide prevention and control engineering, shear strength, sliding weight degree, pore water pressure and seepage pressure of sliding zone soil are often taken as important parameters for slope stability analysis and engineering design of prevention and control, while the variation law of stress and strain of landslide rock and soil mass in the process of rainfall is seldom considered. In this paper, based on the constitutive model of gravel soil and the law of soil stress and strain change during rainfall infiltration, numerical simulation method is adopted to analyze the stability of a certain gravel soil landslide by considering factors such as permeability coefficient, runoff coefficient and infiltration intensity, then reveal the distribution of pore pressure and stress in the gravel soil landslide under the influence of rainfall infiltration combined with the observation of the landslide, as to provide theoretical basis for prevention and control ofthe landslide.
2019, 27(s1): 207-213.
Debris flow is one of the common geological disasters in Beijing mountainous area. Through field investigation, experiment and calculation, the formation conditions and development characteristics of Dongtuogu gully are analyzed in detail, and the related movement characteristics are calculated. On this basis, the risk, susceptibility and risk of Dongtuogu gully were evaluated by selecting evaluation factors. The research results are of great significance to the prevention and control of debris flow disaster in Dongtuogu gully.
Debris flow is one of the common geological disasters in Beijing mountainous area. Through field investigation, experiment and calculation, the formation conditions and development characteristics of Dongtuogu gully are analyzed in detail, and the related movement characteristics are calculated. On this basis, the risk, susceptibility and risk of Dongtuogu gully were evaluated by selecting evaluation factors. The research results are of great significance to the prevention and control of debris flow disaster in Dongtuogu gully.
2019, 27(s1): 214-223.
The Wenchuan area is a frequent area of debris flow disasters, and there is a narrow and steep debris flow. The narrow and steep debris flow has the characteristics of large longitudinal slope gradient, large reserves of provenance and large scale of rushing out. Therefore, it is necessary to pay attention to the prevention and control of debris flow in the disaster area. In this paper, the well-balanced numerical method is used to study the narrow and steep debris flow in Wenchuan area. The flow process and flow depth of each burst frequency are studied by taking the Wa Yaogou in MianChi Town, Wenchuan County as an example. The simulation results were interpreted from the topography and fluid energy directions. The well-balanced numerical method can well handle the debris flow migration problem of complex terrain, and more accurate simulation results can be obtained for the narrow and steep debris flow. According to the simulation results, the solid matter of the debris flow with a 2%burst frequency is 1.87×104 m3,the maximum punching length is 185 m, the stacking area of the stacking fan is 2.88×104 m2, and the reliability of the method is determined by comparison. The study of its flow process shows that the migration process of the narrow and steep debris flow is closely related to the topography of the debris flow ditch:the fluid energy gradually accumulates in the curve region, and the maximum value of the flow energy and flow velocity of the debris flow in the linear channel region is downstream. The sloping flow of the mudslide reaches a maximum at a relatively gentle slope, and finally rushes out of the gully. Based on the above conclusions, it provides working methods and reasonable engineering suggestions for the treatment and prevention of narrow and steep debris flow disasters in WenChuan.
The Wenchuan area is a frequent area of debris flow disasters, and there is a narrow and steep debris flow. The narrow and steep debris flow has the characteristics of large longitudinal slope gradient, large reserves of provenance and large scale of rushing out. Therefore, it is necessary to pay attention to the prevention and control of debris flow in the disaster area. In this paper, the well-balanced numerical method is used to study the narrow and steep debris flow in Wenchuan area. The flow process and flow depth of each burst frequency are studied by taking the Wa Yaogou in MianChi Town, Wenchuan County as an example. The simulation results were interpreted from the topography and fluid energy directions. The well-balanced numerical method can well handle the debris flow migration problem of complex terrain, and more accurate simulation results can be obtained for the narrow and steep debris flow. According to the simulation results, the solid matter of the debris flow with a 2%burst frequency is 1.87×104 m3,the maximum punching length is 185 m, the stacking area of the stacking fan is 2.88×104 m2, and the reliability of the method is determined by comparison. The study of its flow process shows that the migration process of the narrow and steep debris flow is closely related to the topography of the debris flow ditch:the fluid energy gradually accumulates in the curve region, and the maximum value of the flow energy and flow velocity of the debris flow in the linear channel region is downstream. The sloping flow of the mudslide reaches a maximum at a relatively gentle slope, and finally rushes out of the gully. Based on the above conclusions, it provides working methods and reasonable engineering suggestions for the treatment and prevention of narrow and steep debris flow disasters in WenChuan.
2019, 27(s1): 224-229.
In order to ensure the safety of the foundation pit excavation, we select the foundation pit engineering of a substation as the research object, based on the geotechnical engineering investigation report, the geological model based on the site drilling data and engineering geological section is established by means of geological modeling technology. The ABAQUS simulation software was used to simulate the foundation pit excavation. The Mohr-Coulomb elastoplastic constitutive model was used to calculate the nonlinear properties on the foundation. The discontinuous contact characteristics between the underground continuous wall and the soil were described by penalty function algorithm. By calculating the characteristics of soil deformation, surface settlement and foundation uplift in different excavation stages, combined with substation design requirements and site engineering geological conditions, it provides basis for foundation pit excavation construction. The results show that the amount of ground settlement behind the wall, the amount of basal uplift and the horizontal displacement of the soil behind the wall present a regular change with the process of excavation. Compared with the rough modeling, the model is built according to the results of engineering geological exploration, which can better reflect the actual situation of soil stability.
In order to ensure the safety of the foundation pit excavation, we select the foundation pit engineering of a substation as the research object, based on the geotechnical engineering investigation report, the geological model based on the site drilling data and engineering geological section is established by means of geological modeling technology. The ABAQUS simulation software was used to simulate the foundation pit excavation. The Mohr-Coulomb elastoplastic constitutive model was used to calculate the nonlinear properties on the foundation. The discontinuous contact characteristics between the underground continuous wall and the soil were described by penalty function algorithm. By calculating the characteristics of soil deformation, surface settlement and foundation uplift in different excavation stages, combined with substation design requirements and site engineering geological conditions, it provides basis for foundation pit excavation construction. The results show that the amount of ground settlement behind the wall, the amount of basal uplift and the horizontal displacement of the soil behind the wall present a regular change with the process of excavation. Compared with the rough modeling, the model is built according to the results of engineering geological exploration, which can better reflect the actual situation of soil stability.
2019, 27(s1): 230-237.
Taking the slope of longshan substation engineering area as the research object, based on the borehole data and geophysical data, using 3D geological modeling technology and AutoCAD software, the typical geological profile of the slope of substation engineering area was established. The geological profile was imported into the finite element simulation software ABAQUS to obtain the slope numerical model. The stability of slope in engineering area was quantitatively analyzed by strength reduction method. Meanwhile, the influence of different anti-slide pile position on slope stability was studied. The simulation results show that:The plastic strain contour can determine the position of the potential slip plane, and the strength reduction coefficient corresponding to the abrupt displacement point can be used as the slope safety factor. The position of anti-slide pile has a great influence on the potential sliding surface of slope. When anti-slide pile is located in the middle and lower part of the slope, it can effectively prevent the sliding deformation of the upper soil mass, and the lower soil mass will not produce new plastic zone. At this time, the safety factor of slope is the largest, and the effect of anti-slide pile reinforcement is the best. The numerical simulation results can provide important guidance for slope protection design.
Taking the slope of longshan substation engineering area as the research object, based on the borehole data and geophysical data, using 3D geological modeling technology and AutoCAD software, the typical geological profile of the slope of substation engineering area was established. The geological profile was imported into the finite element simulation software ABAQUS to obtain the slope numerical model. The stability of slope in engineering area was quantitatively analyzed by strength reduction method. Meanwhile, the influence of different anti-slide pile position on slope stability was studied. The simulation results show that:The plastic strain contour can determine the position of the potential slip plane, and the strength reduction coefficient corresponding to the abrupt displacement point can be used as the slope safety factor. The position of anti-slide pile has a great influence on the potential sliding surface of slope. When anti-slide pile is located in the middle and lower part of the slope, it can effectively prevent the sliding deformation of the upper soil mass, and the lower soil mass will not produce new plastic zone. At this time, the safety factor of slope is the largest, and the effect of anti-slide pile reinforcement is the best. The numerical simulation results can provide important guidance for slope protection design.
2019, 27(s1): 238-243.
This article is based on a detailed survey of 1:50000 geological disasters in the Ailaoshan area, Remote sensing data comparison interpretation, Analysis the characteristics of the landslide and explor the risk identification of landslide. Research shows:The pore water pressure was enhanced to form a landslide, and the landslide is a high level bedding landslide; Rock mass of different structure types on the left and right sides of the landslide, and determined the clear boundary shape of the landslide; Rock mass composition structure with steep mid-slope orientation, was the basis for landslide slippage; The occurrence of cracks at the trailing edge of the landslide and the collapse of the soil, It was the initial state before the disaster; Infiltration of heavy rainfall is the trigger condition for the occurrence of this landslide; Insufficient understanding of high(out of vision) disasters and weak sense of risk prevention, It was the disaster condition of this landslide. Analysis of landslide critical disaster risk from risk factors, such as landslide boundary morphology, compositional structure, initial state, triggering conditions and disaster conditions. The identification of landslide risk is only a demonstration in the Ailaoshan area, risk identification similar to landslide needs further exploration, and provide technical support for disaster prevention and mitigation decisions in the region.
This article is based on a detailed survey of 1:50000 geological disasters in the Ailaoshan area, Remote sensing data comparison interpretation, Analysis the characteristics of the landslide and explor the risk identification of landslide. Research shows:The pore water pressure was enhanced to form a landslide, and the landslide is a high level bedding landslide; Rock mass of different structure types on the left and right sides of the landslide, and determined the clear boundary shape of the landslide; Rock mass composition structure with steep mid-slope orientation, was the basis for landslide slippage; The occurrence of cracks at the trailing edge of the landslide and the collapse of the soil, It was the initial state before the disaster; Infiltration of heavy rainfall is the trigger condition for the occurrence of this landslide; Insufficient understanding of high(out of vision) disasters and weak sense of risk prevention, It was the disaster condition of this landslide. Analysis of landslide critical disaster risk from risk factors, such as landslide boundary morphology, compositional structure, initial state, triggering conditions and disaster conditions. The identification of landslide risk is only a demonstration in the Ailaoshan area, risk identification similar to landslide needs further exploration, and provide technical support for disaster prevention and mitigation decisions in the region.
2019, 27(s1): 244-250.
Seepage erosion often occurs on slopes of loose weathered residual soil during heavy rainfall. The loss of fine particles caused by this process will change the permeability and strength of slopes, and then affect the stability of shallow slopes. In this paper, the shallow landslides of the Fanzhang Formation in the mountainous area of southern Anhui Province are taken as the research object, and the shear strength and permeability coefficient of the soil under different particle gradation are obtained, and the actual rainfall is simulated by Geo-Studio software(2017.6.3-2017.7.20)Groundwater level dynamic response and landslide stability under action. The results show that:(1)Particle loss has obvious influence on the shear strength index of residual soil, and its cohesive force decreases with the decrease of particle content, and the internal friction angle increases. (2)The groundwater level of landslide body with different particle size distribution has the same effect on rainfall; the decrease of landslide particle will lead to the decrease of groundwater level. (3)The overall stability of landslide is obviously affected by particle size distribution, which decreases with the decrease of internal particles, and the displacement of landslide increases sharply with the heavy rainfall.
Seepage erosion often occurs on slopes of loose weathered residual soil during heavy rainfall. The loss of fine particles caused by this process will change the permeability and strength of slopes, and then affect the stability of shallow slopes. In this paper, the shallow landslides of the Fanzhang Formation in the mountainous area of southern Anhui Province are taken as the research object, and the shear strength and permeability coefficient of the soil under different particle gradation are obtained, and the actual rainfall is simulated by Geo-Studio software(2017.6.3-2017.7.20)Groundwater level dynamic response and landslide stability under action. The results show that:(1)Particle loss has obvious influence on the shear strength index of residual soil, and its cohesive force decreases with the decrease of particle content, and the internal friction angle increases. (2)The groundwater level of landslide body with different particle size distribution has the same effect on rainfall; the decrease of landslide particle will lead to the decrease of groundwater level. (3)The overall stability of landslide is obviously affected by particle size distribution, which decreases with the decrease of internal particles, and the displacement of landslide increases sharply with the heavy rainfall.
2019, 27(s1): 251-256.
The subaqueous debris flow and its huge block transport capacity have attracted wide attention. In this study, a self-developed rotating flume was used to make a stable circulating subaqueous debris flow, and the location of transported block in subaqueous debris flow was measured. The 300-mesh silica sand was used to make the subaqueous debris flow; the blocks such as quartz rock block, PVC block and glass bead was used to observe the transport phenomenon. The observations confirmed that the subaqueous debris flow can transport the block to the vicinity of the head, and the transport capacity is related to the underwater debris flow and the nature of the block:ifthe bulk density is lower than the dense flow density, the subaqueous debris flow can transport the block to the head position; if the bulk density is much larger than the dense flow density, then the block can only be in the tail or middle location of dense flow, always unable to reach the head position; the stability of the block motion in the subaqueous debris flow is related to the thickness of the block. Considering the effects of dense flow rate, density of the block and size of the block, the transport mechanism of blocks by subaqueous debris flow in rotating flume test was proposed.
The subaqueous debris flow and its huge block transport capacity have attracted wide attention. In this study, a self-developed rotating flume was used to make a stable circulating subaqueous debris flow, and the location of transported block in subaqueous debris flow was measured. The 300-mesh silica sand was used to make the subaqueous debris flow; the blocks such as quartz rock block, PVC block and glass bead was used to observe the transport phenomenon. The observations confirmed that the subaqueous debris flow can transport the block to the vicinity of the head, and the transport capacity is related to the underwater debris flow and the nature of the block:ifthe bulk density is lower than the dense flow density, the subaqueous debris flow can transport the block to the head position; if the bulk density is much larger than the dense flow density, then the block can only be in the tail or middle location of dense flow, always unable to reach the head position; the stability of the block motion in the subaqueous debris flow is related to the thickness of the block. Considering the effects of dense flow rate, density of the block and size of the block, the transport mechanism of blocks by subaqueous debris flow in rotating flume test was proposed.
2019, 27(s1): 257-261.
As a kind of special weak structural plane, shear zone has aroused attention and deep understanding of the influence on engineering construction. Rock mass of dam foundation with shear zone of Guxian hydro-junction project is taken as the research object, this paper analyzed the distribution characteristics of shear zone, and determined parameters of shear strength by large in-situ shear test. In the meantime, according to the established calculation formulae of geological strength index(GSI)for rock masses estimated by ultrasonic velocity of rock mass, the rock mass mechanical parameters are predicted by Hoek-Brown criterion. The result shows that equivalent fraction coefficient from Hoek-Brown criterion is lower than test value and cohesion force is far greater than that from shearing test. It is shown by error analysis that the difference between experiment values and estimated ones is mostly induced by the span of minimum principal stress used in Hoek-Brown criterion. For this situation, some cautions and corresponding resolve methods while using Hoek-Brown criterion are reminded. In addition, the proposed method provides a new approach to determine the mechanical parameters of stratified rock mass with shear zone, when test data are scant.
As a kind of special weak structural plane, shear zone has aroused attention and deep understanding of the influence on engineering construction. Rock mass of dam foundation with shear zone of Guxian hydro-junction project is taken as the research object, this paper analyzed the distribution characteristics of shear zone, and determined parameters of shear strength by large in-situ shear test. In the meantime, according to the established calculation formulae of geological strength index(GSI)for rock masses estimated by ultrasonic velocity of rock mass, the rock mass mechanical parameters are predicted by Hoek-Brown criterion. The result shows that equivalent fraction coefficient from Hoek-Brown criterion is lower than test value and cohesion force is far greater than that from shearing test. It is shown by error analysis that the difference between experiment values and estimated ones is mostly induced by the span of minimum principal stress used in Hoek-Brown criterion. For this situation, some cautions and corresponding resolve methods while using Hoek-Brown criterion are reminded. In addition, the proposed method provides a new approach to determine the mechanical parameters of stratified rock mass with shear zone, when test data are scant.
2019, 27(s1): 262-268.
On June 30, 2012, a large number of co-seismic landslides were triggered by the MS6.6 earthquake at the junction of Hejing County and Xinyuan County in Xinjiang. 306 landslides were interpreted and delineated from the IKONOS remote sensing image whose resolution is 1 m after the earthquake. Most of the landslides were small, Elevation, earthquake intensity, slope, distance to fault, curvature, aspect, slope position, distance to roads, distance to drainage sand lithology were selected as the influencing factors of the earthquake landslides. Rasterized the layers of influence factors on the platform of Geographic Information System(GIS),the aim of this study was to apply logistic regression model for the Hejing earthquake triggered landslide hazard mapping, and then divided research area into extremely high hazard zone, high hazard zone, middle hazard zone, low hazard zone, extremely low hazard zone, and the map of landslide hazard assessment was obtained. The ROC curve was used to validate the prediction results. The result shows that the AUC value of the training sample set is 0.80,which indicates that the accuracy of the LR model is ideal. The final conclusion in the paper provides a reference for disaster prevention and mitigation of landslides in the earthquake zone.
On June 30, 2012, a large number of co-seismic landslides were triggered by the MS6.6 earthquake at the junction of Hejing County and Xinyuan County in Xinjiang. 306 landslides were interpreted and delineated from the IKONOS remote sensing image whose resolution is 1 m after the earthquake. Most of the landslides were small, Elevation, earthquake intensity, slope, distance to fault, curvature, aspect, slope position, distance to roads, distance to drainage sand lithology were selected as the influencing factors of the earthquake landslides. Rasterized the layers of influence factors on the platform of Geographic Information System(GIS),the aim of this study was to apply logistic regression model for the Hejing earthquake triggered landslide hazard mapping, and then divided research area into extremely high hazard zone, high hazard zone, middle hazard zone, low hazard zone, extremely low hazard zone, and the map of landslide hazard assessment was obtained. The ROC curve was used to validate the prediction results. The result shows that the AUC value of the training sample set is 0.80,which indicates that the accuracy of the LR model is ideal. The final conclusion in the paper provides a reference for disaster prevention and mitigation of landslides in the earthquake zone.
2019, 27(s1): 269-275.
On October 10 and November 3, 2018, two successive large-scale landslides occurred in Baige Village, Polo Township, Jiangda County, Changdu City, Tibet, and blocked the Jinsha River, caused widespread social concern. Geometric shape and volume of landslides are key issues and important foundation for landslide mechanism research and prevention and mitigation of landslide disaster. To this end, these date include the digital orthophoto map(DOM) and digital elevation model(DEM)taken by UAV,pre-slide 30 m DEM from ASTER GDEM and the Planet images with 3 m resolution are collected. The pre-slide terrain contours are hand painted based on the after-slide terrain contours and pre-slide micro topography. Then, based on the topography before and after the landslides, volume calculation is carried out on the ArcGIS software. In addition, several cross sections are plotted with AutoCAD,based on which the depth characteristics are analyzed. The study shows that the volume and geometric features of landslide can be obtained by this method, which can provide references for similar landslide hazards research.
On October 10 and November 3, 2018, two successive large-scale landslides occurred in Baige Village, Polo Township, Jiangda County, Changdu City, Tibet, and blocked the Jinsha River, caused widespread social concern. Geometric shape and volume of landslides are key issues and important foundation for landslide mechanism research and prevention and mitigation of landslide disaster. To this end, these date include the digital orthophoto map(DOM) and digital elevation model(DEM)taken by UAV,pre-slide 30 m DEM from ASTER GDEM and the Planet images with 3 m resolution are collected. The pre-slide terrain contours are hand painted based on the after-slide terrain contours and pre-slide micro topography. Then, based on the topography before and after the landslides, volume calculation is carried out on the ArcGIS software. In addition, several cross sections are plotted with AutoCAD,based on which the depth characteristics are analyzed. The study shows that the volume and geometric features of landslide can be obtained by this method, which can provide references for similar landslide hazards research.
2019, 27(s1): 276-288.
In Huaying mountain, the geological structure is very complex, mining and other human engineering activities are intense, and geological hazards are well developed. Taking the middle section of Huaying mountiainas the study area. Based on fully collecting the latest geological hazard database and field investigation, the law of development and distribution of geological hazards is analyzed from the aspects of topography and landform, geological structure, River erosion, surface cover and human engineering activities. The weanalyzed the sensitivity of hazard-brewing factors based on the WOE model. Innovatively, the variance of relative coefficient of evidence weight is used as sensitivity index. Finally, two sensitivity indices are used to quantitatively analyze the influence degree of each hazard-brewing factor on the development and distribution of geological hazards. The results show that:(1)The spatial distribution of geological hazards is obviously different and uneven. Geological hazards mainly distribute along the piedmont zones on both sides of Huaying Mountain. The geological hazards on the western slope are more developed than those on the eastern slope. (2)The influences of hazard-brewing factors on the development of geological hazards are obviously different. The sensitivity of geological hazards to engineering geological formations factor is the highest. Engineering geological formations, slope heights, mining development and surface cover play a relatively strong role in controlling the development of geological hazards. Highway construction and river erosion play a weak role in controlling the development of geological hazards. (3)Using sensitivity analysis method based on WOE model, we can quantitatively analyzed the influence of hazard-brewing factors on the development of geological hazards. This method is scientific, reliable, convenient and feasible. The research results can not only provide scientific basis for the prevention and control of geological hazards in Huaying Mountain, but also provide new ideas for the study of the relationship between hazard-brewing factors and geological hazards and the sensitivity of geological hazards.
In Huaying mountain, the geological structure is very complex, mining and other human engineering activities are intense, and geological hazards are well developed. Taking the middle section of Huaying mountiainas the study area. Based on fully collecting the latest geological hazard database and field investigation, the law of development and distribution of geological hazards is analyzed from the aspects of topography and landform, geological structure, River erosion, surface cover and human engineering activities. The weanalyzed the sensitivity of hazard-brewing factors based on the WOE model. Innovatively, the variance of relative coefficient of evidence weight is used as sensitivity index. Finally, two sensitivity indices are used to quantitatively analyze the influence degree of each hazard-brewing factor on the development and distribution of geological hazards. The results show that:(1)The spatial distribution of geological hazards is obviously different and uneven. Geological hazards mainly distribute along the piedmont zones on both sides of Huaying Mountain. The geological hazards on the western slope are more developed than those on the eastern slope. (2)The influences of hazard-brewing factors on the development of geological hazards are obviously different. The sensitivity of geological hazards to engineering geological formations factor is the highest. Engineering geological formations, slope heights, mining development and surface cover play a relatively strong role in controlling the development of geological hazards. Highway construction and river erosion play a weak role in controlling the development of geological hazards. (3)Using sensitivity analysis method based on WOE model, we can quantitatively analyzed the influence of hazard-brewing factors on the development of geological hazards. This method is scientific, reliable, convenient and feasible. The research results can not only provide scientific basis for the prevention and control of geological hazards in Huaying Mountain, but also provide new ideas for the study of the relationship between hazard-brewing factors and geological hazards and the sensitivity of geological hazards.
2019, 27(s1): 289-295.
Based on the surveying results of geological hazard investigation, the development characteristics of geological hazard in the Yanzihe river basin were analyzed. Then, the failure modes of landslide and rockfall were studied. Results shows that the geological hazards in the study area are mainly consist of landslides, rockfallsand debris flows. Those disasters are mainly located in the valley slopes especially in the Kangxian County-Yangba town road where human activities are concentrated. Most of the geological hazardsare occurred during the rainy season from July to September. The landslides are mainly in small scale and occurred within shallow cover layers. The main type of rock fall is in small scale and are occurred in low rocky slopes. Then, the majority of debris flowswereoccurred in valley and driven by rainstorms. From the aspect of failure modes:most of the rock could be classified as fracturing-load falling, bending-topping and fracturing-sliding; the landslides could be classified as creep-tension creaking and sliding-tension cracking. The results offers technical support for geological hazard prevention, town planning, landuse and so on.
Based on the surveying results of geological hazard investigation, the development characteristics of geological hazard in the Yanzihe river basin were analyzed. Then, the failure modes of landslide and rockfall were studied. Results shows that the geological hazards in the study area are mainly consist of landslides, rockfallsand debris flows. Those disasters are mainly located in the valley slopes especially in the Kangxian County-Yangba town road where human activities are concentrated. Most of the geological hazardsare occurred during the rainy season from July to September. The landslides are mainly in small scale and occurred within shallow cover layers. The main type of rock fall is in small scale and are occurred in low rocky slopes. Then, the majority of debris flowswereoccurred in valley and driven by rainstorms. From the aspect of failure modes:most of the rock could be classified as fracturing-load falling, bending-topping and fracturing-sliding; the landslides could be classified as creep-tension creaking and sliding-tension cracking. The results offers technical support for geological hazard prevention, town planning, landuse and so on.
2019, 27(s1): 296-305.
The heights of filling body in the North-east of Panzhihua Baoanying airport reach 128 meters, which is rare among the high slopes in China. The 12th Landslide has occurred 5 times sliding and 2 times strong deformation since the airport was built in 2001, and its cause of formation has always been doubtful. The formation and evolution process and influencing factors of the 12th landslide are analyzed and summarized systematically by collecting data. With the help of on-site investigation, monitoring, drilling and laboratory test, the mechanism of deformation and failure of landslide in recent two times is revealed emphatically. The results show that internal factors of the slope sliding many times include special groove topography, abundant underground water in the slope and special rock mass structure, and rainfall, earthquake and surcharge are the external factors. The mechanism of the last two deformations can be summarized as the thrust-type sliding caused by the resistance of the front of the anti-slide pile and the loading of the trailing edge, and then turns to creep-cracking fracture failure mode under the action of groundwater softening. The corresponding prevention and control countermeasures are put forward and the results of the study provide a useful reference for the understanding of multi-stage and secondary sliding mechanism of high fill slope and engineering treatment。
The heights of filling body in the North-east of Panzhihua Baoanying airport reach 128 meters, which is rare among the high slopes in China. The 12th Landslide has occurred 5 times sliding and 2 times strong deformation since the airport was built in 2001, and its cause of formation has always been doubtful. The formation and evolution process and influencing factors of the 12th landslide are analyzed and summarized systematically by collecting data. With the help of on-site investigation, monitoring, drilling and laboratory test, the mechanism of deformation and failure of landslide in recent two times is revealed emphatically. The results show that internal factors of the slope sliding many times include special groove topography, abundant underground water in the slope and special rock mass structure, and rainfall, earthquake and surcharge are the external factors. The mechanism of the last two deformations can be summarized as the thrust-type sliding caused by the resistance of the front of the anti-slide pile and the loading of the trailing edge, and then turns to creep-cracking fracture failure mode under the action of groundwater softening. The corresponding prevention and control countermeasures are put forward and the results of the study provide a useful reference for the understanding of multi-stage and secondary sliding mechanism of high fill slope and engineering treatment。
2019, 27(s1): 306-310.
The great shearing deformation energy is accumulated in locked segment under the action of huge thrust of the upper slope body, and shear strength suddenly drop owing to peak-residual strength drop when sliding surface extend. Once the locked segment is suddenly snipped, the elastic strain energy is converted into the kinetic energy of the sliding mass. In order to study the calculation method of landslide elastic strain energy under seismic load, this paper attempted to obtain the shear strain energy of the locking solid and the peak residual strength reduction strain energy based on elastic mechanics method applying seismic force as physical strength to the micro-body. Consequently, this paper took an attempt to obtain the starting velocity formula of sliding mass on account of Kinetic energy theorem. The new method was verified by an example, and the resultindicates that the speed formula is reasonable.
The great shearing deformation energy is accumulated in locked segment under the action of huge thrust of the upper slope body, and shear strength suddenly drop owing to peak-residual strength drop when sliding surface extend. Once the locked segment is suddenly snipped, the elastic strain energy is converted into the kinetic energy of the sliding mass. In order to study the calculation method of landslide elastic strain energy under seismic load, this paper attempted to obtain the shear strain energy of the locking solid and the peak residual strength reduction strain energy based on elastic mechanics method applying seismic force as physical strength to the micro-body. Consequently, this paper took an attempt to obtain the starting velocity formula of sliding mass on account of Kinetic energy theorem. The new method was verified by an example, and the resultindicates that the speed formula is reasonable.
2019, 27(s1): 311-318.
As a new type of geotechnical structure, the deformation and stability characteristics of reinforced soil structures will be affected by various internal and external factors. The internal factors mainly include the length and stiffness of the reinforcement, spacing, panel type, the dense of fillings, et al. At present, a lot of related researches have been done and much experience has been accumulated. However, there are relatively a few studies on the influence of external factors which mainly include earthquake, rainfall, traffic load and so on. There are some researches on the dynamic behaviors of reinforced soil structures under earthquake loads and traffic loads has been done, but little attention was paid on the influence of rainfall, especially under the combined effect of dynamic loads and rainfall. Based on the analysis of a large number of literatures, this paper discusses the research statusregarding to three influences of reinforced soil stability:dynamic load, rainfall ad their combined effect. What's more, some deficiencies of these researches will be pointed out. It is believed that the study on the stability of reinforced soil under the combined effect of dynamic load and rainfall is significant in practices, and that under complex environmental conditions will become the focus and development direction in the future.
As a new type of geotechnical structure, the deformation and stability characteristics of reinforced soil structures will be affected by various internal and external factors. The internal factors mainly include the length and stiffness of the reinforcement, spacing, panel type, the dense of fillings, et al. At present, a lot of related researches have been done and much experience has been accumulated. However, there are relatively a few studies on the influence of external factors which mainly include earthquake, rainfall, traffic load and so on. There are some researches on the dynamic behaviors of reinforced soil structures under earthquake loads and traffic loads has been done, but little attention was paid on the influence of rainfall, especially under the combined effect of dynamic loads and rainfall. Based on the analysis of a large number of literatures, this paper discusses the research statusregarding to three influences of reinforced soil stability:dynamic load, rainfall ad their combined effect. What's more, some deficiencies of these researches will be pointed out. It is believed that the study on the stability of reinforced soil under the combined effect of dynamic load and rainfall is significant in practices, and that under complex environmental conditions will become the focus and development direction in the future.
2019, 27(s1): 319-326.
The rapid classification of surrounding rock during construction period is an important task of "dynamic design and dynamic construction" of mountain tunnels. Based on the long-term geological cooperation of a highway tunnel construction in Beijing, we have selected the rock strength, the number of joints, the structural plane state, the relationship between the dominant structural plane and the tunnel axis, and the groundwater as the surrounding rock quality grading index, and studied the rapid acquisition methods of each grading index, and then established a table scoring method that combines qualitative and quantitative grading indicators. The TRT advanced geological prediction system can better reflect the geological conditions in front of the tunnel face. And we have systematically summarized cluster anomalies, single anomalies, fault anomalies, and interbed anomalies in the TRT forecasting system. The authors proposed a dynamic fast grading method for surrounding rock during construction period, which is combining table scoring method with TRT advanced geological prediction. This method can predict the "invisible" geological information in front of the tunnel face based on the "visible" geological information of the excavated tunnel face. And this method has strong operability and high coincidence rate with actual geological conditions and has important guiding significance for tunnel construction.
The rapid classification of surrounding rock during construction period is an important task of "dynamic design and dynamic construction" of mountain tunnels. Based on the long-term geological cooperation of a highway tunnel construction in Beijing, we have selected the rock strength, the number of joints, the structural plane state, the relationship between the dominant structural plane and the tunnel axis, and the groundwater as the surrounding rock quality grading index, and studied the rapid acquisition methods of each grading index, and then established a table scoring method that combines qualitative and quantitative grading indicators. The TRT advanced geological prediction system can better reflect the geological conditions in front of the tunnel face. And we have systematically summarized cluster anomalies, single anomalies, fault anomalies, and interbed anomalies in the TRT forecasting system. The authors proposed a dynamic fast grading method for surrounding rock during construction period, which is combining table scoring method with TRT advanced geological prediction. This method can predict the "invisible" geological information in front of the tunnel face based on the "visible" geological information of the excavated tunnel face. And this method has strong operability and high coincidence rate with actual geological conditions and has important guiding significance for tunnel construction.
2019, 27(s1): 327-333.
The paper selected the goaf located at Xinhua-Ying'an section of planned Dandong-Altai National Highway as the engineering background. We established the goaf model based on a finite difference software(FLAC3D)to study the deformation pattern of the overburden layer and ground surface under geostatic stress. We also obtained the stress-strain pattern in the mining process. The analysis results show that the original geological state is changed due to the exploitation of underground coal seams. The maximum principal stress occurs at the boundary of the goaf and the roof, and obvious stress concentration occurs. In the upper part of the roof, the maximum principal stress gradually increases from the top to the bottom, and compressive main stress is predominant. Settlement deformation and failure are most likely to occur at the roof of goaf, and the vertical displacement increases with the reduction of the distance to the top of the goaf and vice versa. The vertical displacement of the rock formation with the away from the goaf is gradually reduced. The subsidence basin is asymmetrical. The maximum displacement of the surface subsidence occurs at the downhill side of the middle of the subsidence basin. The settlement displacement reaches a maximum value of 791 mm after the mining of the multi-level goaf. We calculated the maximum settlement value of the study area by the theoretical calculation of the probability integral method, and the calculation result is 830 mm, which is consistent with the result got by FLAC3D numerical simulation method.
The paper selected the goaf located at Xinhua-Ying'an section of planned Dandong-Altai National Highway as the engineering background. We established the goaf model based on a finite difference software(FLAC3D)to study the deformation pattern of the overburden layer and ground surface under geostatic stress. We also obtained the stress-strain pattern in the mining process. The analysis results show that the original geological state is changed due to the exploitation of underground coal seams. The maximum principal stress occurs at the boundary of the goaf and the roof, and obvious stress concentration occurs. In the upper part of the roof, the maximum principal stress gradually increases from the top to the bottom, and compressive main stress is predominant. Settlement deformation and failure are most likely to occur at the roof of goaf, and the vertical displacement increases with the reduction of the distance to the top of the goaf and vice versa. The vertical displacement of the rock formation with the away from the goaf is gradually reduced. The subsidence basin is asymmetrical. The maximum displacement of the surface subsidence occurs at the downhill side of the middle of the subsidence basin. The settlement displacement reaches a maximum value of 791 mm after the mining of the multi-level goaf. We calculated the maximum settlement value of the study area by the theoretical calculation of the probability integral method, and the calculation result is 830 mm, which is consistent with the result got by FLAC3D numerical simulation method.
2019, 27(s1): 334-339.
The safety assessment of radioactive waste disposal site involves a large space-time scale and complex systems. The calculation of nuclide migration inevitably has uncertainty. The treatment of uncertainty plays a key role in safety assessment results. This paper takes a low and medium level solid waste disposal site as an example. We used Ecolego program to analyze the uncertainty of parameters, and calculated the process of nuclide migration in groundwater and its impact on public after the disposal site closing. The results show that the model is mainly affected by dispersion, followed by density and distribution coefficient. The nuclide concentration is negatively correlated with these parameters.
The safety assessment of radioactive waste disposal site involves a large space-time scale and complex systems. The calculation of nuclide migration inevitably has uncertainty. The treatment of uncertainty plays a key role in safety assessment results. This paper takes a low and medium level solid waste disposal site as an example. We used Ecolego program to analyze the uncertainty of parameters, and calculated the process of nuclide migration in groundwater and its impact on public after the disposal site closing. The results show that the model is mainly affected by dispersion, followed by density and distribution coefficient. The nuclide concentration is negatively correlated with these parameters.
2019, 27(s1): 340-347.
Landslide dams are formed by the collapse, landslide, mudslide and other unstable bodies. Due to the short lifespan of the dam and the long affected basin, the existing methods are difficult to assessment the dynamic risk of entire disaster evolution process across the basin. In this paper, a dynamic risk analysis method was proposed based on geometric parameters of the dam, the three-dimensional topographic information of the river and the population distribution data. Besides, the dynamic risk analysis of the Tangjiashan landslide dam was carried out, and quantitative risk value of the downstream was obtained. The results show that the risk level of the risk zone is generally negatively correlated with the distance, the closer the dam site is,the higher the risk is. The dynamic evolution of the risk is usually delayed, when the risk zone near the dam site receives the risk, there is still no risk in the distant area; while the risks in the nearby begin to dissipate, the risks in the distant areas increase. The analysis results are in good agreement with the actual risk situation of the Tangjiashan landslide dam, which has important reference value for later risk management.
Landslide dams are formed by the collapse, landslide, mudslide and other unstable bodies. Due to the short lifespan of the dam and the long affected basin, the existing methods are difficult to assessment the dynamic risk of entire disaster evolution process across the basin. In this paper, a dynamic risk analysis method was proposed based on geometric parameters of the dam, the three-dimensional topographic information of the river and the population distribution data. Besides, the dynamic risk analysis of the Tangjiashan landslide dam was carried out, and quantitative risk value of the downstream was obtained. The results show that the risk level of the risk zone is generally negatively correlated with the distance, the closer the dam site is,the higher the risk is. The dynamic evolution of the risk is usually delayed, when the risk zone near the dam site receives the risk, there is still no risk in the distant area; while the risks in the nearby begin to dissipate, the risks in the distant areas increase. The analysis results are in good agreement with the actual risk situation of the Tangjiashan landslide dam, which has important reference value for later risk management.
2019, 27(s1): 348-355.
Landslide dams usually formed by collapse, landslide, debris flow, et al.,which have the characteristics of sudden formation and great dangerous. If the dam breaching, it is easy to flood the downstream area by surges and cause huge loss of life and property. However, the study of rapid stability assessment of landslide dams is greatly restricted due to its various geometrical shapes, inhomogeneous material composition and complex internal structure. In this paper, a database with 1757 landslide dams from all over the world was compiled. The influences of dam characteristic parameters(triggers, hydrology/geometric parameters, materials) and dam stability are analyzed. Rainfall-induced dam and the dam with soil material have the worst stability, mainly because of the material particles of rainfall-induced landslide dam are relatively small water content, while the soil landslide dams usually have poor permeability and low impact velocity. Besides, the dam stability first increase and then decrease with dam height and lake volume increase because of when the dam height is too small, it's easy to overflow and when the dam height too high, the reservoir water potential energy increases. The dam stability increases with the dam width and dam volume increase, the main reason is that with the dam width and volume increase will increase the resistance of the dam to sliding. The dam stability decreases with the average discharge increase, the reason is that the increase of the inflow rate reduces the overflow time. It is also found that landslide dam stability cannot be predicted by one or two influence factors since it is affected by multi factors. Based on seven dimensionless variables, a rapid evaluation model for estimating the stability is developed. The accuracy of the model is 85.1%. The model developed in this paper show better accuracy due to considering dam materials and triggers. Case studies(Jiala landslide dams) are presented to show the application of the model developed in this paper.
Landslide dams usually formed by collapse, landslide, debris flow, et al.,which have the characteristics of sudden formation and great dangerous. If the dam breaching, it is easy to flood the downstream area by surges and cause huge loss of life and property. However, the study of rapid stability assessment of landslide dams is greatly restricted due to its various geometrical shapes, inhomogeneous material composition and complex internal structure. In this paper, a database with 1757 landslide dams from all over the world was compiled. The influences of dam characteristic parameters(triggers, hydrology/geometric parameters, materials) and dam stability are analyzed. Rainfall-induced dam and the dam with soil material have the worst stability, mainly because of the material particles of rainfall-induced landslide dam are relatively small water content, while the soil landslide dams usually have poor permeability and low impact velocity. Besides, the dam stability first increase and then decrease with dam height and lake volume increase because of when the dam height is too small, it's easy to overflow and when the dam height too high, the reservoir water potential energy increases. The dam stability increases with the dam width and dam volume increase, the main reason is that with the dam width and volume increase will increase the resistance of the dam to sliding. The dam stability decreases with the average discharge increase, the reason is that the increase of the inflow rate reduces the overflow time. It is also found that landslide dam stability cannot be predicted by one or two influence factors since it is affected by multi factors. Based on seven dimensionless variables, a rapid evaluation model for estimating the stability is developed. The accuracy of the model is 85.1%. The model developed in this paper show better accuracy due to considering dam materials and triggers. Case studies(Jiala landslide dams) are presented to show the application of the model developed in this paper.
2019, 27(s1): 356-360.
Gaoyangshan hot spring in Sanmenxia is located at the turning point of Fen-Wei Graben, with complex structure and concentrated stress. Lingbao-Sanmenxia deep fault is more than 1000 m apart and its influence depth is more than 3000 m. It forms a channel of geothermal rise and constitutes a convective geothermal system by fracture cycle. Near Wentang, there are many secondary faults in the rock mass, and the runoff conditions are good. Therefore, this is good condition for storing underground hot water. Because of Gaoyangshan fault uplift, Cenozoic and Quaternary aquifuges on the hanging wall, the hot water excretes to the surface as an overflow spring.
Gaoyangshan hot spring in Sanmenxia is located at the turning point of Fen-Wei Graben, with complex structure and concentrated stress. Lingbao-Sanmenxia deep fault is more than 1000 m apart and its influence depth is more than 3000 m. It forms a channel of geothermal rise and constitutes a convective geothermal system by fracture cycle. Near Wentang, there are many secondary faults in the rock mass, and the runoff conditions are good. Therefore, this is good condition for storing underground hot water. Because of Gaoyangshan fault uplift, Cenozoic and Quaternary aquifuges on the hanging wall, the hot water excretes to the surface as an overflow spring.
2019, 27(s1): 361-366.
Rational development and utilization of urban underground space is of great significance for improving urban environment, building livable cities and enhancing urban comprehensive carrying capacity. 3D geological modeling is the most commonly used technology to directly reflect the geological conditions below the surface, which is widely used in the development and utilization planning of underground space. The fifth national new district "Lanzhou New Area" is located in the Qin Wang Chuan Basin, and its development and utilization of the underground space must be based on a full understanding of the geological conditions. In this paper, the engineering geological drilling data was used as the data of 3D geological modeling. The 3D geological model of the Qin Wang Chuan Basin was established by using GMS software, and the surface elevation was modified by using DEM data. By comparison, it is found that the modified model is closer to the real situation on the surface, and overcomes the model distortion caused by the interpolation of the borehole elevation. The model shows the geomorphological features and strata spatial distribution of the Qin Wang Chuan Basin, which has a certain reference value for the underground space planning and construction of Lanzhou New Area.
Rational development and utilization of urban underground space is of great significance for improving urban environment, building livable cities and enhancing urban comprehensive carrying capacity. 3D geological modeling is the most commonly used technology to directly reflect the geological conditions below the surface, which is widely used in the development and utilization planning of underground space. The fifth national new district "Lanzhou New Area" is located in the Qin Wang Chuan Basin, and its development and utilization of the underground space must be based on a full understanding of the geological conditions. In this paper, the engineering geological drilling data was used as the data of 3D geological modeling. The 3D geological model of the Qin Wang Chuan Basin was established by using GMS software, and the surface elevation was modified by using DEM data. By comparison, it is found that the modified model is closer to the real situation on the surface, and overcomes the model distortion caused by the interpolation of the borehole elevation. The model shows the geomorphological features and strata spatial distribution of the Qin Wang Chuan Basin, which has a certain reference value for the underground space planning and construction of Lanzhou New Area.
2019, 27(s1): 367-370.
High-density electrical method plays an important role in karst exploration, and can effectively detect the location, shape, scale and filling of karst development zone. In this paper, several typical karst geoelectric models are established, and their high-density electrical response is calculated and analyzed. Combined with engineering examples, it is considered that the method of combining the pseudo-section of measured data with the quantitative inversion profile can improve the method to identify the abnormal bodies.
High-density electrical method plays an important role in karst exploration, and can effectively detect the location, shape, scale and filling of karst development zone. In this paper, several typical karst geoelectric models are established, and their high-density electrical response is calculated and analyzed. Combined with engineering examples, it is considered that the method of combining the pseudo-section of measured data with the quantitative inversion profile can improve the method to identify the abnormal bodies.
2019, 27(s1): 371-378.
In order to study the response characteristics of rock slopes under dynamic load, a simple model test method was designed. Based on the prototype of the Guantan landslide, following the law of similitude, a physical model test device is built to research on seismic response of the model slope with different input wave frequencies, excitation directions and amplitudes. The main conclusions are drawn as follows:The slope had vertical and free face amplification for the incident wave, and the amplification effect is more significant with the measuring point closing to the surface. Besides, dynamic response characteristics of the model are affected by the frequency and the direction of the incident wave, and there is a positive correlation between the acceleration amplification coefficient P and the amplitude of the incident wave. The results show that this simple method is able to reflect the seismic dynamic response characteristics of rock slopes, meanwhile, it is inexpensive, flexible and convenient.
In order to study the response characteristics of rock slopes under dynamic load, a simple model test method was designed. Based on the prototype of the Guantan landslide, following the law of similitude, a physical model test device is built to research on seismic response of the model slope with different input wave frequencies, excitation directions and amplitudes. The main conclusions are drawn as follows:The slope had vertical and free face amplification for the incident wave, and the amplification effect is more significant with the measuring point closing to the surface. Besides, dynamic response characteristics of the model are affected by the frequency and the direction of the incident wave, and there is a positive correlation between the acceleration amplification coefficient P and the amplitude of the incident wave. The results show that this simple method is able to reflect the seismic dynamic response characteristics of rock slopes, meanwhile, it is inexpensive, flexible and convenient.
2019, 27(s1): 379-385.
In recent years, with the rapid development of industry, transportation and urbanization in China, engineering construction is increased at a rapid rate, which is followed by various engineering problems. Among them, the most notable problem is the slope failure. In particular, in the construction of high-speed railway, airport, urban area and other projects with long distance and large area, excavation or backfilling has led to emergence of a large number of artificial slopes, breaking the balance of the original slopes. Therefore, it is of great importance to study the slope protection methods and technologies. Among slope protection methods, the vegetation slope protection technology is widely used because of its low cost and good effect. While current researches on the mechanism and implementation of the vegetation slope protection are scattered. We classify and summary the relevant research results of vegetation slope protection from two aspects:hydrological effect and mechanical effect of vegetation slope protection reinforcement mechanism. We concluded that:(1)the hydrological effect is embodied in the rainfall interception effect of the vegetation slope protection; (2)the mechanical effect is embodied in the root-soil interaction, which increases the shear strength of slope soils; (3)the reinforcement mechanism is the reinforcing effect of short roots on slope soils, the anchoring effect of long roots and the flushing-and weathering-preventing effect on slope surface. In general, a lot of experimental investigations and numerical simulations have been performed on the reinforcement mechanism and key technologies of the vegetation slope protection technology. However, there are still insufficient quantitative analysis in this field. The hydrological and mechanical effects of the vegetation slope protection have been commonly separated, however, in actual, they superimpose on each other and work together on the slope. In addition, studies on the selection of plants and the methods of vegetation conservation in practice are insufficient.
In recent years, with the rapid development of industry, transportation and urbanization in China, engineering construction is increased at a rapid rate, which is followed by various engineering problems. Among them, the most notable problem is the slope failure. In particular, in the construction of high-speed railway, airport, urban area and other projects with long distance and large area, excavation or backfilling has led to emergence of a large number of artificial slopes, breaking the balance of the original slopes. Therefore, it is of great importance to study the slope protection methods and technologies. Among slope protection methods, the vegetation slope protection technology is widely used because of its low cost and good effect. While current researches on the mechanism and implementation of the vegetation slope protection are scattered. We classify and summary the relevant research results of vegetation slope protection from two aspects:hydrological effect and mechanical effect of vegetation slope protection reinforcement mechanism. We concluded that:(1)the hydrological effect is embodied in the rainfall interception effect of the vegetation slope protection; (2)the mechanical effect is embodied in the root-soil interaction, which increases the shear strength of slope soils; (3)the reinforcement mechanism is the reinforcing effect of short roots on slope soils, the anchoring effect of long roots and the flushing-and weathering-preventing effect on slope surface. In general, a lot of experimental investigations and numerical simulations have been performed on the reinforcement mechanism and key technologies of the vegetation slope protection technology. However, there are still insufficient quantitative analysis in this field. The hydrological and mechanical effects of the vegetation slope protection have been commonly separated, however, in actual, they superimpose on each other and work together on the slope. In addition, studies on the selection of plants and the methods of vegetation conservation in practice are insufficient.
2019, 27(s1): 386-391.
A large number of vertical macropores are developed in loess. The vectorization of vertical macropores in loess is the basis and difficulty of the study of fabric constitutive relations of loess. Based on industrial CT scanning and beads chain filling method, this paper develops a set of software for vectorization and characterization of loess macropores. The specific functions of the software implementation are:1)CT scan reconstruction of the 3D model of loess macropores; 2)automatic filling and pore separation of the loess ball chain; 3)Automatic statistics of the distribution characteristics of single pores; 4)Calculation of fabric tensor and fabric tensor coefficient of loess macropores model based on Stereology technology. The results show that the beads chain filling method and the developed software can vectorize the fabric characteristics of loess pores. The software lays a foundation for the fabric description of loess.
A large number of vertical macropores are developed in loess. The vectorization of vertical macropores in loess is the basis and difficulty of the study of fabric constitutive relations of loess. Based on industrial CT scanning and beads chain filling method, this paper develops a set of software for vectorization and characterization of loess macropores. The specific functions of the software implementation are:1)CT scan reconstruction of the 3D model of loess macropores; 2)automatic filling and pore separation of the loess ball chain; 3)Automatic statistics of the distribution characteristics of single pores; 4)Calculation of fabric tensor and fabric tensor coefficient of loess macropores model based on Stereology technology. The results show that the beads chain filling method and the developed software can vectorize the fabric characteristics of loess pores. The software lays a foundation for the fabric description of loess.
2019, 27(s1): 392-396.
Geothermal energy is a kind of green renewable energy. How to detect geothermal anomaly area accurately and quickly has become an urgent problem. Shallow ground temperature survey can obtain ground temperature dataquickly, which can identify geothermal anomaly area. Wecarried out field experiments in the Houpu area of Xiamen by shallow ground temperature survey and obtained the temperature and in-situ thermal conductivity of 1~2 m depth. Based on the data acquired by shallow ground temperature survey, we analyzed the temperature distribution characteristics of the 2 m depth in the study area and delineated the geothermal anomaly area. We established aprediction model of ground temperature based on one-dimensional steady-state heat conduction theory. According to the field experiment data of shallow ground temperature survey, we predicted the temperature distribution of the constant temperature layer in the study area and compared it with the measured temperature. The results show that the prediction model of ground temperature is accurate and the temperature contour map of constant temperature layer can more accurately reflect the actual situation of geothermal anomaly. Shallow ground temperature survey and it's data analysis method can be used as an effective means in the early stage of geothermal exploration.
Geothermal energy is a kind of green renewable energy. How to detect geothermal anomaly area accurately and quickly has become an urgent problem. Shallow ground temperature survey can obtain ground temperature dataquickly, which can identify geothermal anomaly area. Wecarried out field experiments in the Houpu area of Xiamen by shallow ground temperature survey and obtained the temperature and in-situ thermal conductivity of 1~2 m depth. Based on the data acquired by shallow ground temperature survey, we analyzed the temperature distribution characteristics of the 2 m depth in the study area and delineated the geothermal anomaly area. We established aprediction model of ground temperature based on one-dimensional steady-state heat conduction theory. According to the field experiment data of shallow ground temperature survey, we predicted the temperature distribution of the constant temperature layer in the study area and compared it with the measured temperature. The results show that the prediction model of ground temperature is accurate and the temperature contour map of constant temperature layer can more accurately reflect the actual situation of geothermal anomaly. Shallow ground temperature survey and it's data analysis method can be used as an effective means in the early stage of geothermal exploration.
2019, 27(s1): 397-404.
Accurately understanding and evaluating the development law of karst and the degree of karst development are the key to solving the problem of karst geological disasters. In combination with the current situation that the evaluation of karst development in tunnel construction mainly relies on the exposure of geological information by the tunnel surface, in order to solve the technical problems of classification surrounding karst rock and karst development in advance geological forecast, to realize rapid and quantitative identification of karst development in the tunnel. The author based on the results obtained by the National Natural Surface Project Research Institute-the hydrochemical dynamics-fractal index evaluation technology of karst development degree, and compiled the prediction and evaluation software for tunnel karst development degree system. The system mainly includes geological information in the survey and design stage, karst geological information during construction, prediction and evaluation of karst development degree based on geological information of the first two stages, system management and maintenance, document preservation and report printing, et al. Through the field data collection and analysis, integrated various tunnel construction The on-site information can instantly predict the karst development in a certain range in front of the tunnel face, determine the degree of karst development, it could combine the karst tunnel geological prediction geophysical test results to achieve rapid on-site quantitative identification of tunnel karst development, improve accuracy of karst geological prediction, and further provide a geological reference for the prevention and control of karst tunnel geological disasters.
Accurately understanding and evaluating the development law of karst and the degree of karst development are the key to solving the problem of karst geological disasters. In combination with the current situation that the evaluation of karst development in tunnel construction mainly relies on the exposure of geological information by the tunnel surface, in order to solve the technical problems of classification surrounding karst rock and karst development in advance geological forecast, to realize rapid and quantitative identification of karst development in the tunnel. The author based on the results obtained by the National Natural Surface Project Research Institute-the hydrochemical dynamics-fractal index evaluation technology of karst development degree, and compiled the prediction and evaluation software for tunnel karst development degree system. The system mainly includes geological information in the survey and design stage, karst geological information during construction, prediction and evaluation of karst development degree based on geological information of the first two stages, system management and maintenance, document preservation and report printing, et al. Through the field data collection and analysis, integrated various tunnel construction The on-site information can instantly predict the karst development in a certain range in front of the tunnel face, determine the degree of karst development, it could combine the karst tunnel geological prediction geophysical test results to achieve rapid on-site quantitative identification of tunnel karst development, improve accuracy of karst geological prediction, and further provide a geological reference for the prevention and control of karst tunnel geological disasters.
2019, 27(s1): 405-410.
Affected by the change of underground factors, the heritage buildings often have uneven settlement of foundation and cracks on the wall, which seriously influence the safe of the heritage buildings. Aiming at the damage influenced by the deformation of the air-raid shelter of Longmu Temple in Beisong Zhuang, Shanxi Province, the high density resistivity nondestructive survey method is used to measure the cracks and uneven settlement of foundation on site. The results present the distribution area of the air-raid shelter accurately, which provide important data support for the protection of Longmu Temple and the scheme of governing the underground environments. The practical results indicates that the high density electrical nondestructive survey method is an important detection method for the underground structure of heritage buildings. The high density electrical nondestructive survey method has the characteristics of nondestructive and speediness, and accords with the basic principles of cultural relics protection.
Affected by the change of underground factors, the heritage buildings often have uneven settlement of foundation and cracks on the wall, which seriously influence the safe of the heritage buildings. Aiming at the damage influenced by the deformation of the air-raid shelter of Longmu Temple in Beisong Zhuang, Shanxi Province, the high density resistivity nondestructive survey method is used to measure the cracks and uneven settlement of foundation on site. The results present the distribution area of the air-raid shelter accurately, which provide important data support for the protection of Longmu Temple and the scheme of governing the underground environments. The practical results indicates that the high density electrical nondestructive survey method is an important detection method for the underground structure of heritage buildings. The high density electrical nondestructive survey method has the characteristics of nondestructive and speediness, and accords with the basic principles of cultural relics protection.
2019, 27(s1): 411-417.
In order to study the distribution characteristics of ultimate side resistance of even-section piles in weathered sandstone, field tests were carried out on the basis of the national network Pingfule 500 kilovolt double-circuit project. According to the test results, the ultimate side resistance of 11 even-section piles was analyzed. The results show that the value of ultimate side resistance of pile increases linearly with the increase of soil depth; in strong/moderately weathered sandstone, the ultimate side resistance of pile increases with the increase of embedded rock depth. In this test site, the average ultimate side resistance of soil layer, strongly weathered sandstone layer and moderately weathered sandstone layer is 91.3 kPa, 456.83 kPa and 1015.3 kPa respectively. Comparing with the current codes, it is found that the calculation results of the codes are conservative. The test results in this paper have certain reference significance for the design of uplift piles in similar strata.
In order to study the distribution characteristics of ultimate side resistance of even-section piles in weathered sandstone, field tests were carried out on the basis of the national network Pingfule 500 kilovolt double-circuit project. According to the test results, the ultimate side resistance of 11 even-section piles was analyzed. The results show that the value of ultimate side resistance of pile increases linearly with the increase of soil depth; in strong/moderately weathered sandstone, the ultimate side resistance of pile increases with the increase of embedded rock depth. In this test site, the average ultimate side resistance of soil layer, strongly weathered sandstone layer and moderately weathered sandstone layer is 91.3 kPa, 456.83 kPa and 1015.3 kPa respectively. Comparing with the current codes, it is found that the calculation results of the codes are conservative. The test results in this paper have certain reference significance for the design of uplift piles in similar strata.
2019, 27(s1): 418-424.
It is always a difficult problem to accurately predict the possibility and severity of rock burst in high geostress area. After years of research, domestic and foreign scholars have proposed a variety of rock burst criteria based on the formation mechanism and occurrence conditions of rock burst. However, these criteria are based solely on a single factor or a single engineering case that causes rock burst, analyzing the stress of surrounding rock and the rock burst tendency index when rock burst occurs, and then dividing the rock burst level. This article collected and categorized the occurrence of 203 rock burst cases, of which 36 cases collected more comprehensive rock mechanics parameters and rock burst orientation indexes. By adapting a variety of rock burst criterion index to forecast and statistically analyze the level of rock burst in engineering case and comparing it with the actual rock burst, it finds that stress criterion of σθmax/σc index and energy criterion of Wet index is highly accurate, up to 88.9%, and the stress criterion of σ1/σc target accuracy is low, only 44.4%. This paper obtains the probability map of rock burst degree grade accuracy by different criteria of rockburst case. The analysis results can provide a reference for effective prediction of rock burst in high ground stress region.
It is always a difficult problem to accurately predict the possibility and severity of rock burst in high geostress area. After years of research, domestic and foreign scholars have proposed a variety of rock burst criteria based on the formation mechanism and occurrence conditions of rock burst. However, these criteria are based solely on a single factor or a single engineering case that causes rock burst, analyzing the stress of surrounding rock and the rock burst tendency index when rock burst occurs, and then dividing the rock burst level. This article collected and categorized the occurrence of 203 rock burst cases, of which 36 cases collected more comprehensive rock mechanics parameters and rock burst orientation indexes. By adapting a variety of rock burst criterion index to forecast and statistically analyze the level of rock burst in engineering case and comparing it with the actual rock burst, it finds that stress criterion of σθmax/σc index and energy criterion of Wet index is highly accurate, up to 88.9%, and the stress criterion of σ1/σc target accuracy is low, only 44.4%. This paper obtains the probability map of rock burst degree grade accuracy by different criteria of rockburst case. The analysis results can provide a reference for effective prediction of rock burst in high ground stress region.
2019, 27(s1): 425-430.
Geotechnical physical and mechanical parameters are particularly important in the design and construction of civil engineering. They are not only related to the quality and safety of Engineering construction, but also closely related to the selection of structural design, cost and progress of engineering. In order to fully apply these precious data to engineering construction, In this paper, I sorted the data of physical and mechanical parameters of three types of rocks recorded in the Handbook of Rock Mechanics Parameters and analyzed the correlation between the five indexs of rock(the dry compressive strength, the wet compressive strength, bulk density, water absorption, elastic modulus) by means of mathematical statistics. The results show that:1)The dry and wet compressive strength, modulus of elasticity and bulk density of rockobey normal distribution; however, the water absorption index of rock does not obey normal distribution; 2)There is a strong linear relationship between dry and wet compressive strength of rock; 3)The compressive strength of rock is positively correlated with its elastic modulus and bulk density but negatively correlated with its water absorption. Finally, according to the statistical results, the empirical formulas among the strongly correlated parameters are established, which can provide references for geotechnical engineering construction.
Geotechnical physical and mechanical parameters are particularly important in the design and construction of civil engineering. They are not only related to the quality and safety of Engineering construction, but also closely related to the selection of structural design, cost and progress of engineering. In order to fully apply these precious data to engineering construction, In this paper, I sorted the data of physical and mechanical parameters of three types of rocks recorded in the Handbook of Rock Mechanics Parameters and analyzed the correlation between the five indexs of rock(the dry compressive strength, the wet compressive strength, bulk density, water absorption, elastic modulus) by means of mathematical statistics. The results show that:1)The dry and wet compressive strength, modulus of elasticity and bulk density of rockobey normal distribution; however, the water absorption index of rock does not obey normal distribution; 2)There is a strong linear relationship between dry and wet compressive strength of rock; 3)The compressive strength of rock is positively correlated with its elastic modulus and bulk density but negatively correlated with its water absorption. Finally, according to the statistical results, the empirical formulas among the strongly correlated parameters are established, which can provide references for geotechnical engineering construction.
2019, 27(s1): 431-438.
Karst rocky desertification(KRD)has been posing a threat to the ecological environment and restraining the sustainable development of local economy and society in China's karst areas. The development of rocky desertification is closely related to not only the soil surface runoff loss and underground leakage but also the formation of the overlying red clay. To explore the weathering characteristics of carbonate rocks and its relationship with Karst rocky desertification, the limestone and the dolomite samples collected from the Zhenfeng-Guanling Huajiang Rock Desertification Demonstration Area were carries for leaching experiments. The results show that,(1)The wet-hot conditions can increase the dissolution rate of carbonate, and the increasing extent of dolomite is larger than that of limestone; the particle size has no significant effect on the limestone, while the particle size has a significant effect on the elution rate of dolomite, showing that the smaller the particle size, the faster the dissolution rate. There is a strong correlation between the total leaching rate of carbonate rocks and the leaching rate of Ca2+. (2)Limestone is more prone to dissolution than dolomite. Differential dissolution occurs intensely on the surface and interior of limestone, forming a large number of dissolved pores(pores and holes),resulting in very serious soil erosion. Rocky desertification is prone to occur in the area and the degree of rocky desertification is serious. The control of rocky desertification in limestone area should pay attention to the differential dissolution of limestone, retain the existing soil and improve the ability of water conservation of geological body to accelerate weathering. Dolomite joints and fissures are well developed, which are prone to physical weathering and disintegration, forming uniform gravel and gravel soil. The broken fine particles are beneficial to weathering, but the surface soil layer is thin and the water retention is poor, so it is difficult for plants to grow. In dolomite desertification area, water retention ability of the soil should be improved, wet weathering environment should be created, to promote dolomite weathering.
Karst rocky desertification(KRD)has been posing a threat to the ecological environment and restraining the sustainable development of local economy and society in China's karst areas. The development of rocky desertification is closely related to not only the soil surface runoff loss and underground leakage but also the formation of the overlying red clay. To explore the weathering characteristics of carbonate rocks and its relationship with Karst rocky desertification, the limestone and the dolomite samples collected from the Zhenfeng-Guanling Huajiang Rock Desertification Demonstration Area were carries for leaching experiments. The results show that,(1)The wet-hot conditions can increase the dissolution rate of carbonate, and the increasing extent of dolomite is larger than that of limestone; the particle size has no significant effect on the limestone, while the particle size has a significant effect on the elution rate of dolomite, showing that the smaller the particle size, the faster the dissolution rate. There is a strong correlation between the total leaching rate of carbonate rocks and the leaching rate of Ca2+. (2)Limestone is more prone to dissolution than dolomite. Differential dissolution occurs intensely on the surface and interior of limestone, forming a large number of dissolved pores(pores and holes),resulting in very serious soil erosion. Rocky desertification is prone to occur in the area and the degree of rocky desertification is serious. The control of rocky desertification in limestone area should pay attention to the differential dissolution of limestone, retain the existing soil and improve the ability of water conservation of geological body to accelerate weathering. Dolomite joints and fissures are well developed, which are prone to physical weathering and disintegration, forming uniform gravel and gravel soil. The broken fine particles are beneficial to weathering, but the surface soil layer is thin and the water retention is poor, so it is difficult for plants to grow. In dolomite desertification area, water retention ability of the soil should be improved, wet weathering environment should be created, to promote dolomite weathering.
2019, 27(s1): 439-445.
The effects of water on the physical and mechanical properties of shale are of great importance for understanding the hydraulic fracturing treatment and borehole stability in the shale reservoir. This paper aims at giving a systematic review on the experimental studies on this area, including the following aspects:(1)effect of water on the clay mineral contents and micro-structure of shale; (2)effect of water on the acoustic characteristics of shale; and (3)effect of water on the mechanical properties of shale, such as the deformation, strength, and failure behaviors. Based on the state of art of these studies, a discussion is made combining with the engineering problems. This paper will be helpful for understanding the related issues in shale gas exploitation and carrying out deeper researches.
The effects of water on the physical and mechanical properties of shale are of great importance for understanding the hydraulic fracturing treatment and borehole stability in the shale reservoir. This paper aims at giving a systematic review on the experimental studies on this area, including the following aspects:(1)effect of water on the clay mineral contents and micro-structure of shale; (2)effect of water on the acoustic characteristics of shale; and (3)effect of water on the mechanical properties of shale, such as the deformation, strength, and failure behaviors. Based on the state of art of these studies, a discussion is made combining with the engineering problems. This paper will be helpful for understanding the related issues in shale gas exploitation and carrying out deeper researches.
2019, 27(s1): 446-451.
The failure of rock engineering, including tunnels and slopes etc.,generally experience progressive damage by time-dependent behavior of rock mass. In this paper, the stavrite from a dam foundation were studied, and two groups of stepwise stress uniaxial relaxation tests were conducted. The stress relaxation behaviors as well as its stress relaxation rate under different stress conditions were analyzed. Test results showed that the stress relaxation could be divided into three stages:rapid relaxation stage, deceleration relaxation stage and stable stress stage, and stress relaxation behaviors are closely related to the cracking behaviors and viscous deformation. Finally, a nonlinear Maxwell model was proposed to describe stress relaxation behaviors, fitting results using this nonlinear Maxwell model present a good agreement with test results.
The failure of rock engineering, including tunnels and slopes etc.,generally experience progressive damage by time-dependent behavior of rock mass. In this paper, the stavrite from a dam foundation were studied, and two groups of stepwise stress uniaxial relaxation tests were conducted. The stress relaxation behaviors as well as its stress relaxation rate under different stress conditions were analyzed. Test results showed that the stress relaxation could be divided into three stages:rapid relaxation stage, deceleration relaxation stage and stable stress stage, and stress relaxation behaviors are closely related to the cracking behaviors and viscous deformation. Finally, a nonlinear Maxwell model was proposed to describe stress relaxation behaviors, fitting results using this nonlinear Maxwell model present a good agreement with test results.
2019, 27(s1): 452-459.
H/F discrimination method is used to discriminate the permeable deformation type of crushed gravel with continuous gradation. In order to verify its suitability by a testing method, the permeable deformation testing results are analyzed statistically for 92 samples from 28 projects. The results indicate that the coincidence rate is up to 87.0by comparing the discrimination results of permeable deformation type of continuous gradation crushed gravel through H/F discrimination method and testing results. It shows that the H/F discrimination method is applicable to the continuous gradation crushed gravel.
H/F discrimination method is used to discriminate the permeable deformation type of crushed gravel with continuous gradation. In order to verify its suitability by a testing method, the permeable deformation testing results are analyzed statistically for 92 samples from 28 projects. The results indicate that the coincidence rate is up to 87.0by comparing the discrimination results of permeable deformation type of continuous gradation crushed gravel through H/F discrimination method and testing results. It shows that the H/F discrimination method is applicable to the continuous gradation crushed gravel.
2019, 27(s1): 460-465.
Backfill mining is an method that control the ground pressure and constrain the surrounding rock mass deformation. With thecontinuous development of mining, the backfill volum growth is rapid. The stress distribution of backfill is sectionalized. The study is aim to analyse the large backfill located in the No.2 mine area of Jinchuan Nickel Mine. It is large span and large volum. Monitoring data could indicate the feature of subarea distribution of backfill stress. Then the numerical simulation model is studied the principal stress of represented area nodes and drea the Mohr's circle. The characters of fracture are anticipated. The study could provide some suggestion for the following mining engineering and support measure.
Backfill mining is an method that control the ground pressure and constrain the surrounding rock mass deformation. With thecontinuous development of mining, the backfill volum growth is rapid. The stress distribution of backfill is sectionalized. The study is aim to analyse the large backfill located in the No.2 mine area of Jinchuan Nickel Mine. It is large span and large volum. Monitoring data could indicate the feature of subarea distribution of backfill stress. Then the numerical simulation model is studied the principal stress of represented area nodes and drea the Mohr's circle. The characters of fracture are anticipated. The study could provide some suggestion for the following mining engineering and support measure.
2019, 27(s1): 466-473.
The silt has high organic content, strong compressibility and low mechanical strength, which can easily lead to engineering geological disasters such as uneven settlement or subsidence of the building(structure). Among the silt, the empty frame structure is a prominent feature of the microstructure of the Southern China silt. The uneven distribution of matter and pores leads to the difficulty of extracting the representative microstructure profile, which restricts the in-depth study of the microscopic macroscopic properties of the soil. We analyzed the microstructure of Daya Bay silt by synchrotron radiation micro-CT technology, and construct the continuous structure of the non-destructive sample, which avoids the blindness of single structure section extraction. In order to avoid the influence of time and space and the three-dimensional spatial dispersion of the structural data of the sample, we studied quantitative data such as spectral data analysis and sample number dispersion degree in depth. Then we quantified and discussed the basic structure data such as void ratio and shape coefficient. In the main consolidation process, the dispersion ratio of the sample data such as the void ratio and shape coefficient in the three-dimensional space increases first and then decreases. In the secondary consolidation stage, the dispersion degree of the sample data again shows an increasing trend. The quantitative analysis of the degree of dispersion not only quantifies the degree of non-uniformity of the microstructure during the consolidation process, but also reflects the variation of the sludge in the consolidation. Studies have shown that under increasing consolidation pressure, the sludge exhibits homogeneous-heterogeneous and then homogenized structural evolution characteristics.
The silt has high organic content, strong compressibility and low mechanical strength, which can easily lead to engineering geological disasters such as uneven settlement or subsidence of the building(structure). Among the silt, the empty frame structure is a prominent feature of the microstructure of the Southern China silt. The uneven distribution of matter and pores leads to the difficulty of extracting the representative microstructure profile, which restricts the in-depth study of the microscopic macroscopic properties of the soil. We analyzed the microstructure of Daya Bay silt by synchrotron radiation micro-CT technology, and construct the continuous structure of the non-destructive sample, which avoids the blindness of single structure section extraction. In order to avoid the influence of time and space and the three-dimensional spatial dispersion of the structural data of the sample, we studied quantitative data such as spectral data analysis and sample number dispersion degree in depth. Then we quantified and discussed the basic structure data such as void ratio and shape coefficient. In the main consolidation process, the dispersion ratio of the sample data such as the void ratio and shape coefficient in the three-dimensional space increases first and then decreases. In the secondary consolidation stage, the dispersion degree of the sample data again shows an increasing trend. The quantitative analysis of the degree of dispersion not only quantifies the degree of non-uniformity of the microstructure during the consolidation process, but also reflects the variation of the sludge in the consolidation. Studies have shown that under increasing consolidation pressure, the sludge exhibits homogeneous-heterogeneous and then homogenized structural evolution characteristics.
2019, 27(s1): 474-480.
Scanning electron microscopy(i.e. SEM) is a commonly-used technique for qualitatively analyzing the soil microstructure. It could provide two-dimensional quantitative information on grain-size or pore-size distribution of the soil combining with image processing techniques. However, typically when this method is applied, grey binarization technique is used to distinguish soil particles from pores in a micrograph, which would result in great errors. In the present study, an image processing technique using Photoshop and MATLAB software in combination is proposed, for quantitative analysis of the microstructural characteristics of loess. The proposed technique is used to process the micrographs before and after intact and saturated Malan loess consolidation. The variations of pore-size distribution characteristics due to loading and wetting are interpreted and the influence of microstructure on loess collapsing is understood. The results indicate that the proposed image processing technique in combination with SEM can be used for accurate quantitative analysis on the loess microstructure and its evolution.
Scanning electron microscopy(i.e. SEM) is a commonly-used technique for qualitatively analyzing the soil microstructure. It could provide two-dimensional quantitative information on grain-size or pore-size distribution of the soil combining with image processing techniques. However, typically when this method is applied, grey binarization technique is used to distinguish soil particles from pores in a micrograph, which would result in great errors. In the present study, an image processing technique using Photoshop and MATLAB software in combination is proposed, for quantitative analysis of the microstructural characteristics of loess. The proposed technique is used to process the micrographs before and after intact and saturated Malan loess consolidation. The variations of pore-size distribution characteristics due to loading and wetting are interpreted and the influence of microstructure on loess collapsing is understood. The results indicate that the proposed image processing technique in combination with SEM can be used for accurate quantitative analysis on the loess microstructure and its evolution.
2019, 27(s1): 481-488.
Special soil genesis, grain-size distribution and mineral composition render loess soils poor engineering properties, such as high compressibility and strong collapsibility. This bad characteristic leads to frequent disasters in loess area, and loess needs to be strengthened in order to meet the needs of construction. Compared with traditional strengthening methods, the use of curing agent to reinforce loess soils has advantages of time-saving, labor-saving, low cost and good effect. For this reason, this method has received extensive attention. In this paper, a variety of curing agents which were found to be capable of improving the engineering properties of loess soils effectively are summarized, including nanomaterials, inorganic hardeners, organic polymer materials, biological enzymes and mineralized bacteria. The composition, reinforcement mechanism and reinforcement effect of each curing agent are detailed. Because of small size and large specific surface area, nanomaterials would wrap soil particles to form aggregates of small sizes, which would fill inter-particle or inter-aggregate pores, thus the soil density and uniformity are increased. Inorganic hardeners play the role of cementing and filling in the soil. Organic polymer materials destroy the weak bound water film on the surface of soil particles by ion exchange, the attraction between particles is then improved and the soil density is increased. In addition, organic polymer materials are cements and fillings in the soil structure. Biological enzymes improve the activity of organic macromolecules in the soil through catalysis, resulting inorganic films of cementing and water-blocking functions. Calcium carbonate, the metabolite of mineralized bacteria, would fill soil pores and connect soil particles. On the basis of an insight understanding of the existing researches, we believe that the study of strengthening loess should be paid more attention to:(1)timeliness of the reinforcement effect of curing agents; (2)the application of curing agents in loess engineering, including the construction technology taking account of the difference in engineering conditions; (3)the interaction between environmental factors and strengthening loess with curing agents.
Special soil genesis, grain-size distribution and mineral composition render loess soils poor engineering properties, such as high compressibility and strong collapsibility. This bad characteristic leads to frequent disasters in loess area, and loess needs to be strengthened in order to meet the needs of construction. Compared with traditional strengthening methods, the use of curing agent to reinforce loess soils has advantages of time-saving, labor-saving, low cost and good effect. For this reason, this method has received extensive attention. In this paper, a variety of curing agents which were found to be capable of improving the engineering properties of loess soils effectively are summarized, including nanomaterials, inorganic hardeners, organic polymer materials, biological enzymes and mineralized bacteria. The composition, reinforcement mechanism and reinforcement effect of each curing agent are detailed. Because of small size and large specific surface area, nanomaterials would wrap soil particles to form aggregates of small sizes, which would fill inter-particle or inter-aggregate pores, thus the soil density and uniformity are increased. Inorganic hardeners play the role of cementing and filling in the soil. Organic polymer materials destroy the weak bound water film on the surface of soil particles by ion exchange, the attraction between particles is then improved and the soil density is increased. In addition, organic polymer materials are cements and fillings in the soil structure. Biological enzymes improve the activity of organic macromolecules in the soil through catalysis, resulting inorganic films of cementing and water-blocking functions. Calcium carbonate, the metabolite of mineralized bacteria, would fill soil pores and connect soil particles. On the basis of an insight understanding of the existing researches, we believe that the study of strengthening loess should be paid more attention to:(1)timeliness of the reinforcement effect of curing agents; (2)the application of curing agents in loess engineering, including the construction technology taking account of the difference in engineering conditions; (3)the interaction between environmental factors and strengthening loess with curing agents.
2019, 27(s1): 489-496.
There is a lot of uncertainty in the process of establishing Standard penetration test(SPT)based empirical liquefaction assessment model which inevitably has model uncertainty within it. The database used in this paper contains 8 earthquakes between 1962 and 1976. Adopting the maximum likelihood method, the authors calibrate the model uncertainty of liquefaction discriminants of Code for Seismic Design of Industrial and Civil Buildings(TJ11-74),Code for Seismic Design of Buildings(GB50011-2001) and Code for Seismic Design of Buildings(GB50011-2010). Conclusions are that the three liquefaction discriminants are less accurate in the analysis of case histories before 1974, and the accuracy is higher in the analysis of case histories after 1974. The reason may be that SPT blow counts of case histories before 1974 did not come directly from SPT test. According to Bayesian information criterion, the GB50011-2001 liquefaction discriminant has the highest model probability and fits best the dataset. The result of soil liquefaction discrimination also has model uncertainty. The liquefaction probability of soil can be calculated based on the model error of liquefaction discriminants and the ratio of measured SPT blow counts to critical SPT blow counts.
There is a lot of uncertainty in the process of establishing Standard penetration test(SPT)based empirical liquefaction assessment model which inevitably has model uncertainty within it. The database used in this paper contains 8 earthquakes between 1962 and 1976. Adopting the maximum likelihood method, the authors calibrate the model uncertainty of liquefaction discriminants of Code for Seismic Design of Industrial and Civil Buildings(TJ11-74),Code for Seismic Design of Buildings(GB50011-2001) and Code for Seismic Design of Buildings(GB50011-2010). Conclusions are that the three liquefaction discriminants are less accurate in the analysis of case histories before 1974, and the accuracy is higher in the analysis of case histories after 1974. The reason may be that SPT blow counts of case histories before 1974 did not come directly from SPT test. According to Bayesian information criterion, the GB50011-2001 liquefaction discriminant has the highest model probability and fits best the dataset. The result of soil liquefaction discrimination also has model uncertainty. The liquefaction probability of soil can be calculated based on the model error of liquefaction discriminants and the ratio of measured SPT blow counts to critical SPT blow counts.
2019, 27(s1): 497-504.
The fault zone is usually divided into fault core, broken zone and ternary structure of surrounding rock. As a water diversion structure in a large area, fault fracture zone is the key factor to induce important geological processes. The fracture zone is divided into broken rock, fault breccia and crushed powdery rock. Because the permeability coefficient of broken silt is very low, it controls the water conductivity of the whole fault zone and is a very important part of the water control structure of fault zone. Based on the typical water diversion mud structure in Gansu Province, the permeability coefficients of different structural units in the fracture zone are quantitatively distinguished by several groups of osmotic reverse pressure experiments. The results show that the farther away from the core of the fault zone, the larger the permeability coefficient is, and the variation law of the permeability coefficient is from the broken powder structure(10~9 m·s-1). The permeability coefficient from breccia structure(10-5~10-7 m·s-1)to fragmentation structure(10-4~10-6 m·s-1)increases gradually, and extends to complete bedrock(<10-9 m·s-1). As a major characteristic of pulverized rock, low permeability is characterized by its internal fabric(particle size, pore structure, fracture structure, mineral composition, et al.), and the mechanism of low permeability of shredded rock is interpreted from microscopic aspects. The study has guiding significance for the water conductivity characteristics of the core of the fault zone and the prevention and control of water inrush in the project.
The fault zone is usually divided into fault core, broken zone and ternary structure of surrounding rock. As a water diversion structure in a large area, fault fracture zone is the key factor to induce important geological processes. The fracture zone is divided into broken rock, fault breccia and crushed powdery rock. Because the permeability coefficient of broken silt is very low, it controls the water conductivity of the whole fault zone and is a very important part of the water control structure of fault zone. Based on the typical water diversion mud structure in Gansu Province, the permeability coefficients of different structural units in the fracture zone are quantitatively distinguished by several groups of osmotic reverse pressure experiments. The results show that the farther away from the core of the fault zone, the larger the permeability coefficient is, and the variation law of the permeability coefficient is from the broken powder structure(10~9 m·s-1). The permeability coefficient from breccia structure(10-5~10-7 m·s-1)to fragmentation structure(10-4~10-6 m·s-1)increases gradually, and extends to complete bedrock(<10-9 m·s-1). As a major characteristic of pulverized rock, low permeability is characterized by its internal fabric(particle size, pore structure, fracture structure, mineral composition, et al.), and the mechanism of low permeability of shredded rock is interpreted from microscopic aspects. The study has guiding significance for the water conductivity characteristics of the core of the fault zone and the prevention and control of water inrush in the project.
2019, 27(s1): 505-512.
The hydrochemical of groundwater in the Holocene, Pleistocene, elurium and bedrock fissures in Putian plain was analyzed. The results show that, hydrochemical types of phreatic water are HCO3-Ca, HCO3·Cl-Na·Ca, Cl·HCO3-Na·Ca, Cl-Na, from the mountain to the sea. There are four features:(1)HCO3- and Ca2+are remarkable, it is newly formed, with transient material exchange by the surrounding rock minerals, after the subsurface infiltration,(2)Cl- and Na+ are remarkable, it is sealed ancient seawater,(3)Cl- and Ca2+ are remarkable, Na+ of the groundwater is exchanged with Ca2+ of the minerals in the surrounding rocks,(4)owing to the CO2 dissolved in water, during the precipitation, the HCO3- proportion of the groundwater anion is raised, but the cation composition have stayed the same. Two desalination processes have been found in this article. The first is desalination processes with cation exchange. The second is CO2 dissolved during leaching.
The hydrochemical of groundwater in the Holocene, Pleistocene, elurium and bedrock fissures in Putian plain was analyzed. The results show that, hydrochemical types of phreatic water are HCO3-Ca, HCO3·Cl-Na·Ca, Cl·HCO3-Na·Ca, Cl-Na, from the mountain to the sea. There are four features:(1)HCO3- and Ca2+are remarkable, it is newly formed, with transient material exchange by the surrounding rock minerals, after the subsurface infiltration,(2)Cl- and Na+ are remarkable, it is sealed ancient seawater,(3)Cl- and Ca2+ are remarkable, Na+ of the groundwater is exchanged with Ca2+ of the minerals in the surrounding rocks,(4)owing to the CO2 dissolved in water, during the precipitation, the HCO3- proportion of the groundwater anion is raised, but the cation composition have stayed the same. Two desalination processes have been found in this article. The first is desalination processes with cation exchange. The second is CO2 dissolved during leaching.
2019, 27(s1): 513-518.
The article summarizes the major engineering geological problems existing in Dali-Lincang Railway and Yuxi-Mohan Railway which are building now, and the newly-built Lincang-Qingshuihe Railway and Dali-Lanping Railway. In western Yunnan, there are complex structures, active faults, engineering geological problems such as landslides, mudflow, high ground temperature, high stress, karst, radioactivity, harmful gases, benefic layers, and there are swelling rock(soil) and soft soil distributing in the fault basins. The article serves as a reference and guide for railway construction in the western Yunnan or similar geological conditions.
The article summarizes the major engineering geological problems existing in Dali-Lincang Railway and Yuxi-Mohan Railway which are building now, and the newly-built Lincang-Qingshuihe Railway and Dali-Lanping Railway. In western Yunnan, there are complex structures, active faults, engineering geological problems such as landslides, mudflow, high ground temperature, high stress, karst, radioactivity, harmful gases, benefic layers, and there are swelling rock(soil) and soft soil distributing in the fault basins. The article serves as a reference and guide for railway construction in the western Yunnan or similar geological conditions.
2019, 27(s1): 519-532.
Due to the limitation of topography, economy and planning conditions, Dongge Expressway must be spread in Xiaojiang fault zone. It is the first expressway with all lines located in Xiaojiang fault zone. Xiaojiang fault is a regional Holocene active fault with complex geological conditions along it. The engineering geological characteristics of Xiaojiang fault zone and its different effects on cutting, bridges and tunnels are the primary controlling factors for engineering geological route selection of Dongge Expressway. On the basis of collecting the existing research results of Xiaojiang fault and adopting comprehensive means such as detailed engineering geological mapping, drilling, geophysical prospecting and remote sensing, the engineering geological conditions of several alternative schemes along the Xiaojiang fault zone are accurately analyzed and evaluated, and the junction position of the eastern and Western branches of Xiaojiang fault is preliminarily determined, thus the reasonable route scheme is determined. Several principles for route selection of Expressway Engineering in mountainous areas within Holocene active fault zone are summarized as follows:the main laying methods of the project should be subgrade, short tunnel and low bridge, and the engineering types which are difficult to repair when earthquake damage occurs, such as long tunnel and high bridge, should be used as little as possible; the tunnel engineering should avoid the central position of fault fracture zone or surface fracture zone as far as possible, cross fault fracture zone as short distance as possible, and avoid multiple fault junction positions as possible. Tunnels should be set up and the strike of the line should avoid the mixed accumulation platform or terrace with complex origin in the fault zone as far as possible.
Due to the limitation of topography, economy and planning conditions, Dongge Expressway must be spread in Xiaojiang fault zone. It is the first expressway with all lines located in Xiaojiang fault zone. Xiaojiang fault is a regional Holocene active fault with complex geological conditions along it. The engineering geological characteristics of Xiaojiang fault zone and its different effects on cutting, bridges and tunnels are the primary controlling factors for engineering geological route selection of Dongge Expressway. On the basis of collecting the existing research results of Xiaojiang fault and adopting comprehensive means such as detailed engineering geological mapping, drilling, geophysical prospecting and remote sensing, the engineering geological conditions of several alternative schemes along the Xiaojiang fault zone are accurately analyzed and evaluated, and the junction position of the eastern and Western branches of Xiaojiang fault is preliminarily determined, thus the reasonable route scheme is determined. Several principles for route selection of Expressway Engineering in mountainous areas within Holocene active fault zone are summarized as follows:the main laying methods of the project should be subgrade, short tunnel and low bridge, and the engineering types which are difficult to repair when earthquake damage occurs, such as long tunnel and high bridge, should be used as little as possible; the tunnel engineering should avoid the central position of fault fracture zone or surface fracture zone as far as possible, cross fault fracture zone as short distance as possible, and avoid multiple fault junction positions as possible. Tunnels should be set up and the strike of the line should avoid the mixed accumulation platform or terrace with complex origin in the fault zone as far as possible.
2019, 27(s1): 533-536.
The corrosion test of water and soil is an important content in geotechnical engineering investigation. It refers to the tests of local water and soil to determine the corrosiveness of the building foundation.《Standard for Survey of Geotechnical Engineering》(GB50021-2001):when the concrete structure is above the groundwater level, the corrosive test of soil sample should be taken; When the concrete structure is in ground water or surface water, the corrosive test of water should be taken; When part of the concrete structure is above the water table and part of the concrete structure is below the water table, the corrosive tests of soil samples and water samples should be taken; Only when there is sufficient experience and information to believe that the corrosivity of water and soil are negligible to the building foundation, no water and soil corrosion tests can be conducted. In order to improve the quality of engineering investigations and avoid serious consequences, This paper introduces the evaluation indexes of water and soil corrosion, the indexes include:PH value, Ca2+,Mg2+,Cl-,CO32-,HCO3-,OH-,free CO2,erosive CO2,SO42-,NH4+,total mineralization and the experimental operation methods of the indexes, it summarizes the corrosive effect of each index on the building foundation, the factors that affect the data of each indicator, and the existence relationship between them.
The corrosion test of water and soil is an important content in geotechnical engineering investigation. It refers to the tests of local water and soil to determine the corrosiveness of the building foundation.《Standard for Survey of Geotechnical Engineering》(GB50021-2001):when the concrete structure is above the groundwater level, the corrosive test of soil sample should be taken; When the concrete structure is in ground water or surface water, the corrosive test of water should be taken; When part of the concrete structure is above the water table and part of the concrete structure is below the water table, the corrosive tests of soil samples and water samples should be taken; Only when there is sufficient experience and information to believe that the corrosivity of water and soil are negligible to the building foundation, no water and soil corrosion tests can be conducted. In order to improve the quality of engineering investigations and avoid serious consequences, This paper introduces the evaluation indexes of water and soil corrosion, the indexes include:PH value, Ca2+,Mg2+,Cl-,CO32-,HCO3-,OH-,free CO2,erosive CO2,SO42-,NH4+,total mineralization and the experimental operation methods of the indexes, it summarizes the corrosive effect of each index on the building foundation, the factors that affect the data of each indicator, and the existence relationship between them.
2019, 27(s1): 537-541.
Gadui Hydropower Station utilizes a water level drop of 756 m, in which the maximum water head of the pressure tunnel in front of the penstock plug is 406 M. After the first unit generates electricity, seepage occurs in the hill along the line in the initial stage of operation. When the tunnel was emptied, leakage occurs generally along the line, cracking and uplifting of local lining, shotcrete anchor and floor occur. Later, with the joint efforts of all parties involved in the construction, the characteristics of leakage and damage along the diversion tunnel were identified and targeted measures were taken to effectively control the leakage, eliminate the damage defects, successfully solve the problem of excessive leakage and safe and stable operation of the diversion tunnel.
Gadui Hydropower Station utilizes a water level drop of 756 m, in which the maximum water head of the pressure tunnel in front of the penstock plug is 406 M. After the first unit generates electricity, seepage occurs in the hill along the line in the initial stage of operation. When the tunnel was emptied, leakage occurs generally along the line, cracking and uplifting of local lining, shotcrete anchor and floor occur. Later, with the joint efforts of all parties involved in the construction, the characteristics of leakage and damage along the diversion tunnel were identified and targeted measures were taken to effectively control the leakage, eliminate the damage defects, successfully solve the problem of excessive leakage and safe and stable operation of the diversion tunnel.
2019, 27(s1): 542-548.
Oujiang is the second largest river in Zhejiang province, and Oujiang estuary is a typical area where soft soil is distributed in China. Oujiang estuary has experienced three transgressions in Quaternary Period, and three layers of soft soil was formed ever since. The transgression which happened in Holocene Epoch is the largest in scale, Yetthe deposition history and engineering characteristics of the three layers of soft soil formed duringtransgressions have not been compared or studied. On the basis of studying the deposition history and distribution characteristics of soft soils formed in different deposition stages, the physical and mechanical properties of the soft soil were studied and compered. It was found:as the stratum become newer, the physical properties and the struct of the soft soil become weaker, the sensitivity of the soil become more remarkable. In the relationship between physical and mechanical indexes, the water content of the silty soft soil which is formed in Holocene Epoch is in good linear relationship with wet density, compressibility coefficient and void ratio. As the deposition history extended, the linear relationship between indexes was no longer remarkable, the discreteness enhanced. Specially, as the deposition history extended, the horizontal permeability coefficient enhanced remarkably and the vertical permeability coefficient decreased gradually, the multiple can be up to 10 times.
Oujiang is the second largest river in Zhejiang province, and Oujiang estuary is a typical area where soft soil is distributed in China. Oujiang estuary has experienced three transgressions in Quaternary Period, and three layers of soft soil was formed ever since. The transgression which happened in Holocene Epoch is the largest in scale, Yetthe deposition history and engineering characteristics of the three layers of soft soil formed duringtransgressions have not been compared or studied. On the basis of studying the deposition history and distribution characteristics of soft soils formed in different deposition stages, the physical and mechanical properties of the soft soil were studied and compered. It was found:as the stratum become newer, the physical properties and the struct of the soft soil become weaker, the sensitivity of the soil become more remarkable. In the relationship between physical and mechanical indexes, the water content of the silty soft soil which is formed in Holocene Epoch is in good linear relationship with wet density, compressibility coefficient and void ratio. As the deposition history extended, the linear relationship between indexes was no longer remarkable, the discreteness enhanced. Specially, as the deposition history extended, the horizontal permeability coefficient enhanced remarkably and the vertical permeability coefficient decreased gradually, the multiple can be up to 10 times.
2019, 27(s1): 549-556.
Loess is a typical unsaturated soil, of whom shear strength is an important mechanical property. In order to investigate the unsaturated shear strength characteristics of compacted loess, a series of trixial consolidated draining shear tests(CD test) were conducted on compacted L6 loess of Yan'an, using GDS unsaturated soil triaxial apparatus. The saturation, volume and moisture change of compacted loess were analyzed, and the influence of matric suction and net confining pressure on the stress vs strain relation of compacted loess was discussed. It is found that:The deviatoric stress vs deviatoric strain curves exhibit hardening type, and the volume strain is shear shrinkage at the beginning and then change to dilatancy. Both matric suction and net confining pressure have significant influence on the deformation and strength characteristics of compacted loess, Under the same matric suction condition, the higher the net confining pressure, the higher the strength of the compacted loess sample, the larger the peak value of the shearing shrinkage, and the smaller the dilatancy. As the net confining pressure is constant, the bigger the matric suction, the is stronger the soil strength, the more obvious the dilatancy.
Loess is a typical unsaturated soil, of whom shear strength is an important mechanical property. In order to investigate the unsaturated shear strength characteristics of compacted loess, a series of trixial consolidated draining shear tests(CD test) were conducted on compacted L6 loess of Yan'an, using GDS unsaturated soil triaxial apparatus. The saturation, volume and moisture change of compacted loess were analyzed, and the influence of matric suction and net confining pressure on the stress vs strain relation of compacted loess was discussed. It is found that:The deviatoric stress vs deviatoric strain curves exhibit hardening type, and the volume strain is shear shrinkage at the beginning and then change to dilatancy. Both matric suction and net confining pressure have significant influence on the deformation and strength characteristics of compacted loess, Under the same matric suction condition, the higher the net confining pressure, the higher the strength of the compacted loess sample, the larger the peak value of the shearing shrinkage, and the smaller the dilatancy. As the net confining pressure is constant, the bigger the matric suction, the is stronger the soil strength, the more obvious the dilatancy.
2019, 27(s1): 557-564.
In order to further research the microscopic mechanism of the lignin-modified loess, the pore microscopic characteristics of the lignin-modified loesswithdifferent lignin contents is analyzed based on SEM.Moreover, the variation of microscopic parameters of the lignin-modified loess with different lignin contents is studied based on PCAS.Combined with the unconfined compressive strength test to evaluate the effect of lignin-modified loess. The results show that lignin can effectively fill the pores of loess and enhance the cementation between particles. The content of lignin has a great influence on the microscopic characteristics. Under the curing age of 28 days, the facial porosity, average pore area, pore porosity fractal dimension and average form factor first rapidly decrease and then slowly increase with the increase of lignin content, while the fractal dimension is completely opposite, and the probability entropy of modified loess with the lignin content of 2% and 4% is low. The modified loess with the lignin content of 2%has the highest compressive strength, while too much lignin content will reduce the compressive strength.
In order to further research the microscopic mechanism of the lignin-modified loess, the pore microscopic characteristics of the lignin-modified loesswithdifferent lignin contents is analyzed based on SEM.Moreover, the variation of microscopic parameters of the lignin-modified loess with different lignin contents is studied based on PCAS.Combined with the unconfined compressive strength test to evaluate the effect of lignin-modified loess. The results show that lignin can effectively fill the pores of loess and enhance the cementation between particles. The content of lignin has a great influence on the microscopic characteristics. Under the curing age of 28 days, the facial porosity, average pore area, pore porosity fractal dimension and average form factor first rapidly decrease and then slowly increase with the increase of lignin content, while the fractal dimension is completely opposite, and the probability entropy of modified loess with the lignin content of 2% and 4% is low. The modified loess with the lignin content of 2%has the highest compressive strength, while too much lignin content will reduce the compressive strength.
2019, 27(s1): 565-568.
How to ensure the safety of lining structure is a major and arduous problem faced by tunnel builders in Wudu Tunnel, which is caused by the spalling of initial concrete abutments and the shear failure of steel frames in the fractured zone. According to the deep analysis of large deformation and characteristics of soft rock in Wudu Tunnel, it can be found that the main causes of large deformation of surrounding rock are the influences of fault fracture zone and in-situ stress. Based on the field implementation of different support forms and monitoring data, this paper puts forward reasonable support forms and construction schemes for tunnel passing through large deformation section, which includes adjusting support parameters, reducing the face of excavation as well as closing ring of initial support quickly, and replacing blasting excavation with milling machine. In view of the strong rheological characteristics of soft rock, the disorder of stratum structure and uneven distribution of ground stress across fault section, it is suggested that the deformation rate of the first branch before the second lining of tunnel should be less than 2 mm·d-1, and all construction joints should be set as settlement joints.
How to ensure the safety of lining structure is a major and arduous problem faced by tunnel builders in Wudu Tunnel, which is caused by the spalling of initial concrete abutments and the shear failure of steel frames in the fractured zone. According to the deep analysis of large deformation and characteristics of soft rock in Wudu Tunnel, it can be found that the main causes of large deformation of surrounding rock are the influences of fault fracture zone and in-situ stress. Based on the field implementation of different support forms and monitoring data, this paper puts forward reasonable support forms and construction schemes for tunnel passing through large deformation section, which includes adjusting support parameters, reducing the face of excavation as well as closing ring of initial support quickly, and replacing blasting excavation with milling machine. In view of the strong rheological characteristics of soft rock, the disorder of stratum structure and uneven distribution of ground stress across fault section, it is suggested that the deformation rate of the first branch before the second lining of tunnel should be less than 2 mm·d-1, and all construction joints should be set as settlement joints.
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