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Editor Work2016 Vol. 24, No. 2
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2016, 24(2): 167-180.
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A small scale of loess landslide occurred at Heifangtai in Dangchuan village of Yongjing county. Its occurrence is at 7:50 of April 29, 2015. The site is at the edge of the loess plateau. The instability of loess has a volume of 5104m3. It runs from the forth terrace to the second terrace of the Yellow river. After 3 hours later, however, a large scale of mudstone occurred at this place. Its volume is of 3.5105m3. The mudstone deposit is 780meters long, 100meters wide and the largest thickness of deposit is 17meters. The landslide is one of the few catastrophic landslides. This paper examines the sliding displacement monitoring and the crack distribution. Such examinations are combined with site geological investigation, low-altitude photogrammetry, site engineering geological survey and site moisture content test. This paper analyses the basic characteristics of the landslide and the formation and reasons of landslide by preliminary understanding. The results show that:(1)There are two sliding cases at Dangchuan 2# landslide from the time. There is only one sliding case time in first time sliding and three sliding cases in second times landslide from sliding mode and deposit characteristic. Dangchuan 2# landslide has four times sliding cases in all. (2)The area of the first sliding is 8396m2. Deformation distribution area is only at the edge of plateau and is smaller compared with the sliding area. The long-term creep deformation at the bottom of loess is the inducing factors of the first time landslide. (3)The area of the second sliding is 27422m2. There is rarely any crack at this part and the crack has no obvious deformation before the second times sliding. The liquefaction of the loess at the bottom of landslide plays a very important role in the second times sliding. The landslide has the characteristics such as sudden occurrence, movement long distance and destructive stronger. (4)The Dangchuan section begins to start mass type static liquefaction loess landslide and the boundary of landslide is the sinkholes, which is of great significance that is the research about other section of early recognition of loess landslide and monitoring and early warning of loess landslide.
A small scale of loess landslide occurred at Heifangtai in Dangchuan village of Yongjing county. Its occurrence is at 7:50 of April 29, 2015. The site is at the edge of the loess plateau. The instability of loess has a volume of 5104m3. It runs from the forth terrace to the second terrace of the Yellow river. After 3 hours later, however, a large scale of mudstone occurred at this place. Its volume is of 3.5105m3. The mudstone deposit is 780meters long, 100meters wide and the largest thickness of deposit is 17meters. The landslide is one of the few catastrophic landslides. This paper examines the sliding displacement monitoring and the crack distribution. Such examinations are combined with site geological investigation, low-altitude photogrammetry, site engineering geological survey and site moisture content test. This paper analyses the basic characteristics of the landslide and the formation and reasons of landslide by preliminary understanding. The results show that:(1)There are two sliding cases at Dangchuan 2# landslide from the time. There is only one sliding case time in first time sliding and three sliding cases in second times landslide from sliding mode and deposit characteristic. Dangchuan 2# landslide has four times sliding cases in all. (2)The area of the first sliding is 8396m2. Deformation distribution area is only at the edge of plateau and is smaller compared with the sliding area. The long-term creep deformation at the bottom of loess is the inducing factors of the first time landslide. (3)The area of the second sliding is 27422m2. There is rarely any crack at this part and the crack has no obvious deformation before the second times sliding. The liquefaction of the loess at the bottom of landslide plays a very important role in the second times sliding. The landslide has the characteristics such as sudden occurrence, movement long distance and destructive stronger. (4)The Dangchuan section begins to start mass type static liquefaction loess landslide and the boundary of landslide is the sinkholes, which is of great significance that is the research about other section of early recognition of loess landslide and monitoring and early warning of loess landslide.
2016, 24(2): 181-186.
The clastic rock areas in Guangxi province are distributed widely. There are many geological disasters in these areas. Statistical methods are used to analyze rainfall influence to geological disasters in the clastic rock areas. The factors include the number of rainfall days, rainfall intensity and effective rainfall. Results show that the relation is good between the geological disasters in the clastic rock areas and the rainfall five days before the disaster. The probability of geological disaster is increased greatly when the rainfall intensity is greater than 50mmd-1(rainstorm) or the previous cumulative rainfall is greater than 230mm. The rainfall risk grading standards in the clastic rock areas are determined for warning and forecasting system of geological disasters in Guangxi province.
The clastic rock areas in Guangxi province are distributed widely. There are many geological disasters in these areas. Statistical methods are used to analyze rainfall influence to geological disasters in the clastic rock areas. The factors include the number of rainfall days, rainfall intensity and effective rainfall. Results show that the relation is good between the geological disasters in the clastic rock areas and the rainfall five days before the disaster. The probability of geological disaster is increased greatly when the rainfall intensity is greater than 50mmd-1(rainstorm) or the previous cumulative rainfall is greater than 230mm. The rainfall risk grading standards in the clastic rock areas are determined for warning and forecasting system of geological disasters in Guangxi province.
2016, 24(2): 187-196.
The paper models the dynamic response for dangerous rock mass slope with a bedding structural plane under earthquake loads using the fast lagrangian analysis of continua. Based on time-history analysis method, the law of dynamic response is analyzed and its instability mechanism is also investigated. The results show that there are vertical and free surface amplification effects in the distribution of horizontal acceleration and velocity within the dangerous rock mass slope. The results are obviously influenced by the structural plane, discontinuous phenomena of acceleration, velocity, displacement and shear stress. Its peak horizontal displacements reduce gradually upward when it is below the structural plane, increase suddenly when across the structural plane and continue to reduce gradually upward when above it. Obviously, the amplification factor for horizontal displacement in the dangerous rock mass is larger than that in the mother rock mass. It is conducive to the further study the dynamic characteristics of the structural plane and dynamic instability mechanism for dangerous rock mass slope.
The paper models the dynamic response for dangerous rock mass slope with a bedding structural plane under earthquake loads using the fast lagrangian analysis of continua. Based on time-history analysis method, the law of dynamic response is analyzed and its instability mechanism is also investigated. The results show that there are vertical and free surface amplification effects in the distribution of horizontal acceleration and velocity within the dangerous rock mass slope. The results are obviously influenced by the structural plane, discontinuous phenomena of acceleration, velocity, displacement and shear stress. Its peak horizontal displacements reduce gradually upward when it is below the structural plane, increase suddenly when across the structural plane and continue to reduce gradually upward when above it. Obviously, the amplification factor for horizontal displacement in the dangerous rock mass is larger than that in the mother rock mass. It is conducive to the further study the dynamic characteristics of the structural plane and dynamic instability mechanism for dangerous rock mass slope.
2016, 24(2): 197-203.
This paper estimates the ultimate bearing capacity of foundations on the slope crests. It uses the elasto-plastic finite element method(FEM).It simulates the striping footings on the crest of undrained slopes (u=0). The results show that the ultimate bearing capacity can be expressed as qu=cuNc. When the unit weight of soil is ignored, Nc estimated by FEM is highly agreeable with that calculated by limit analysis. The failure mode is similar to the foundation on the horizontal terrain. When the unit weight of soil is taken into account, the coefficient Nc can be reduced more. The parameter N is defined as the difference of the slope's stability number defined by Taylor from the slope's real state to the limit state. It can be used as determinant. The striping footing's failure can develop into whole slope failure when the N is smaller, as well as foundation failure when the N is bigger. The critical value of N for failure mode change is estimated. Then the Nc-N relationship is constructed. The equation for the ultimate bearing capacity of striping footings on the crest of undrained slopes is built.
This paper estimates the ultimate bearing capacity of foundations on the slope crests. It uses the elasto-plastic finite element method(FEM).It simulates the striping footings on the crest of undrained slopes (u=0). The results show that the ultimate bearing capacity can be expressed as qu=cuNc. When the unit weight of soil is ignored, Nc estimated by FEM is highly agreeable with that calculated by limit analysis. The failure mode is similar to the foundation on the horizontal terrain. When the unit weight of soil is taken into account, the coefficient Nc can be reduced more. The parameter N is defined as the difference of the slope's stability number defined by Taylor from the slope's real state to the limit state. It can be used as determinant. The striping footing's failure can develop into whole slope failure when the N is smaller, as well as foundation failure when the N is bigger. The critical value of N for failure mode change is estimated. Then the Nc-N relationship is constructed. The equation for the ultimate bearing capacity of striping footings on the crest of undrained slopes is built.
2016, 24(2): 204-210.
The Mahalanobis distance discriminant method has a shortage that the weight factors can't be considered. To overcome this shortage, the rough sets theory is used to analyze and obtain weight factors. The weight coefficients are computed by analyzing the support and significance of forecasting method for the predicted object. The weighted distance discriminant models of slope stability evaluation and prediction are established by introducing weight coefficients. According to the characters of slope instability and failure, the rough set and distance discriminant models of slope stability evaluation and prediction are founded, where reasonable indexes are considered and a large set of case engineering samples are taken as raw data and training samples. The validity of rough set and distance discriminant models of slope stability evaluation and prediction have been verified through contrasting with Mahalanobis distance discriminant method, support vector machine and Bayes discriminant analysis. The rough set and distance discriminant models are applied to the slope engineering at some large water control project reservoir area in the middle reaches of Yellow River. The predicting results are according with real situation. The research results show that the rough set and distance discriminant models are reasonable for weight analysis with high prediction accuracy, which is a new and effective method for slope stability analysis and prediction.
The Mahalanobis distance discriminant method has a shortage that the weight factors can't be considered. To overcome this shortage, the rough sets theory is used to analyze and obtain weight factors. The weight coefficients are computed by analyzing the support and significance of forecasting method for the predicted object. The weighted distance discriminant models of slope stability evaluation and prediction are established by introducing weight coefficients. According to the characters of slope instability and failure, the rough set and distance discriminant models of slope stability evaluation and prediction are founded, where reasonable indexes are considered and a large set of case engineering samples are taken as raw data and training samples. The validity of rough set and distance discriminant models of slope stability evaluation and prediction have been verified through contrasting with Mahalanobis distance discriminant method, support vector machine and Bayes discriminant analysis. The rough set and distance discriminant models are applied to the slope engineering at some large water control project reservoir area in the middle reaches of Yellow River. The predicting results are according with real situation. The research results show that the rough set and distance discriminant models are reasonable for weight analysis with high prediction accuracy, which is a new and effective method for slope stability analysis and prediction.
2016, 24(2): 211-219.
Hazard assessment of debris flow is a hot research topic of the disaster science. It is an important task of disaster forecast, prevention and reduction. This paper takes the debris flow gullies atthe dam site in Huoergutu hydropower along Xinjiang Kaidu River as the research area. Based on the studying of the geological environment, it selects eight aspects as evaluation factors. They include debris flow scale, outbreak of the frequency. The weight coefficient of contestant factors is obtained using thegray correlation degree. The risk assessment of debris flow gulliesis evaluated through the qualitative and analogical methods. The results are compared with the results of site-specific debris flowharazd assessment by LIU Xilin. The risk degrees of the Qingshui gully and Xuelian gully using the extension theory are greater than the results of site-specific debris flow harazd assessment, which iscoincided with the filed investigation. Therefore, the grey correlation and extension theory based method for debris flow gullies at the dam site is reasonable and reliable. The method provides reasonable and scientific basis for risk assessment, planning and controlling of debris flows at the dam site.
Hazard assessment of debris flow is a hot research topic of the disaster science. It is an important task of disaster forecast, prevention and reduction. This paper takes the debris flow gullies atthe dam site in Huoergutu hydropower along Xinjiang Kaidu River as the research area. Based on the studying of the geological environment, it selects eight aspects as evaluation factors. They include debris flow scale, outbreak of the frequency. The weight coefficient of contestant factors is obtained using thegray correlation degree. The risk assessment of debris flow gulliesis evaluated through the qualitative and analogical methods. The results are compared with the results of site-specific debris flowharazd assessment by LIU Xilin. The risk degrees of the Qingshui gully and Xuelian gully using the extension theory are greater than the results of site-specific debris flow harazd assessment, which iscoincided with the filed investigation. Therefore, the grey correlation and extension theory based method for debris flow gullies at the dam site is reasonable and reliable. The method provides reasonable and scientific basis for risk assessment, planning and controlling of debris flows at the dam site.
2016, 24(2): 220-227.
The function and effect of check dams and griile dams in certain catchments are studied extensively in China. However, there has been comparatively little research oncontrol measures and their effect to mobilization of debris-flow from landslides. A rainstorm induced debris flow hazard occurred on August 14, 2008 in Yingxiu Town of Sichuan Province, where was affected by the Wenchuan earthquake. The paper examines the motion process and the gully characteristics, landslides blocking point, the high depth of cutting, and their combinations. It is discovered that the whole basin comprehensive treatment shall prevent clogging and cutting. In order to control debris flow disaster happening again, check dams can weaken the leading kinetic energy in the upper reaches of the valley. Retaining plate and bed boards can control the landslide blocking point and protect the toecap in the middle reaches of the valley. Grillage damsand aqueduct can intercept the coarse particle and discharge debris flow smoothly. Then the paper compares the accumulated rainfall, solid matter involved in quantity, dynamic energy reserves and the gully characteristics around control measures. After discussing the initiation, the engineering measures for mobilization of debris-flow from landslides at Shaofang stream course has a good result. It provides a reference for engineering measures for debris-flow mobilization from landslides in the earthquake areas.
The function and effect of check dams and griile dams in certain catchments are studied extensively in China. However, there has been comparatively little research oncontrol measures and their effect to mobilization of debris-flow from landslides. A rainstorm induced debris flow hazard occurred on August 14, 2008 in Yingxiu Town of Sichuan Province, where was affected by the Wenchuan earthquake. The paper examines the motion process and the gully characteristics, landslides blocking point, the high depth of cutting, and their combinations. It is discovered that the whole basin comprehensive treatment shall prevent clogging and cutting. In order to control debris flow disaster happening again, check dams can weaken the leading kinetic energy in the upper reaches of the valley. Retaining plate and bed boards can control the landslide blocking point and protect the toecap in the middle reaches of the valley. Grillage damsand aqueduct can intercept the coarse particle and discharge debris flow smoothly. Then the paper compares the accumulated rainfall, solid matter involved in quantity, dynamic energy reserves and the gully characteristics around control measures. After discussing the initiation, the engineering measures for mobilization of debris-flow from landslides at Shaofang stream course has a good result. It provides a reference for engineering measures for debris-flow mobilization from landslides in the earthquake areas.
2016, 24(2): 228-234.
Debris flow is different from the common landslide. It is a kind of temporary water with sand and stones occurred in a mountainous area. As researches shown, the debris flow is characterized with the nature of Bingham Body and moving jams. Many scholars had made many researches of numerical simulation method, which based on rheology experiment and model. And compared the scope, movement speed and movement time of the debris flow with the actual situation, the numerical simulation programs were developed for the forecast of debris flow. The FLO-2D is one of the software. As engineering practice proved, movement and sedimentary characteristics of debris flow is very important for further study based on the flow characteristics of research on debris flow substance composition. In order to analyze the relationship between debris flow movement-accumulation characteristics and viscosity-yield stress, we simulated the moving characteristics of debris flow by FLO-2D model. Through the analysis, we conclude that debris flow velocity is reduced with the increase of the viscosity, and the reduction is nonlinear. With the increase of yield stress, that is one of the impact factors about debris flow occurrence and stop, flow depth increases. But among the debris flow movement characteristics, the effect between yield stress and debris flow velocity is not obvious. With the increase of the viscosity, the impact force of debris flow decreases. Meanwhile, with the increase of the yield stress, the impact force of debris flow is increased.
Debris flow is different from the common landslide. It is a kind of temporary water with sand and stones occurred in a mountainous area. As researches shown, the debris flow is characterized with the nature of Bingham Body and moving jams. Many scholars had made many researches of numerical simulation method, which based on rheology experiment and model. And compared the scope, movement speed and movement time of the debris flow with the actual situation, the numerical simulation programs were developed for the forecast of debris flow. The FLO-2D is one of the software. As engineering practice proved, movement and sedimentary characteristics of debris flow is very important for further study based on the flow characteristics of research on debris flow substance composition. In order to analyze the relationship between debris flow movement-accumulation characteristics and viscosity-yield stress, we simulated the moving characteristics of debris flow by FLO-2D model. Through the analysis, we conclude that debris flow velocity is reduced with the increase of the viscosity, and the reduction is nonlinear. With the increase of yield stress, that is one of the impact factors about debris flow occurrence and stop, flow depth increases. But among the debris flow movement characteristics, the effect between yield stress and debris flow velocity is not obvious. With the increase of the viscosity, the impact force of debris flow decreases. Meanwhile, with the increase of the yield stress, the impact force of debris flow is increased.
2016, 24(2): 235-245.
The initiation, propagation and coalescence mode of flaws in basalt-like materials with two pro-existing flaws are tested under biaxial cyclic compression. The basalt-like materials contain two pre-existing flaws of 30dip, 20mm length, and 0.3mm thickness, varied rock bridge lengths and dip angles. They are molded using similar materials. The results show that:(1)Under biaxial cyclic compression, the failure progress can be divided into wing crack initiation, wing crack propagation and secondary crack initiation, as well as rock bridge coalescence.(2)The coalescence types include shear coalescence, tensile coalescence and shear-tensile compound coalescence. Nine and eight modes can be distinguished particularly using the two experimental methods.(3)In this paper, shear coalescence under biaxial cyclic compression is more possible than that under biaxial compression. Particularly, the crush and uplift phenomenon in rock bridge only exists in biaxial cyclic compression test.(4)Rock bridge coalescence mode is prominently influenced by rock bridge length and dip. With increasing rock bridge dip, the shear coalescence mode and shear-tensile compound coalescence are more undemanding. Under biaxial compression, the shear coalescence mode is predominant accompanied with increasing rock bridge length. However, this pattern is reversed in biaxial cyclic compression test.
The initiation, propagation and coalescence mode of flaws in basalt-like materials with two pro-existing flaws are tested under biaxial cyclic compression. The basalt-like materials contain two pre-existing flaws of 30dip, 20mm length, and 0.3mm thickness, varied rock bridge lengths and dip angles. They are molded using similar materials. The results show that:(1)Under biaxial cyclic compression, the failure progress can be divided into wing crack initiation, wing crack propagation and secondary crack initiation, as well as rock bridge coalescence.(2)The coalescence types include shear coalescence, tensile coalescence and shear-tensile compound coalescence. Nine and eight modes can be distinguished particularly using the two experimental methods.(3)In this paper, shear coalescence under biaxial cyclic compression is more possible than that under biaxial compression. Particularly, the crush and uplift phenomenon in rock bridge only exists in biaxial cyclic compression test.(4)Rock bridge coalescence mode is prominently influenced by rock bridge length and dip. With increasing rock bridge dip, the shear coalescence mode and shear-tensile compound coalescence are more undemanding. Under biaxial compression, the shear coalescence mode is predominant accompanied with increasing rock bridge length. However, this pattern is reversed in biaxial cyclic compression test.
2016, 24(2): 246-251.
The rock masses in nature usually contain a large number of discontinuities, which results in the anisotropy of rock masses. As one of the important parameters to evaluate rock quality, the generalized RQDt is widely used in rock masses engineering.3D stochastic discrete fracture network method and scan line method are combined to study the spatial distribution regularity of rock quality in different directions. The suggested method is used to study the spatial distribution regularity of dam foundation. Specific steps are as follows:Firstly, based on the probability distribution functions and corresponding statistical parameters investigated in field, 3D stochastic discrete fracture networks are randomly generated using the Monte Carlo Method. Secondly, lots of generalized RQDt can be calculated by setting measuring points and measuring lines. Thirdly, the spatial distribution regularity of rock quality in different directions can be described according to the spatial distribution map. The results indicate that the proposed method is valid and useful for describing the spatial distribution regularity of rock mass quality.
The rock masses in nature usually contain a large number of discontinuities, which results in the anisotropy of rock masses. As one of the important parameters to evaluate rock quality, the generalized RQDt is widely used in rock masses engineering.3D stochastic discrete fracture network method and scan line method are combined to study the spatial distribution regularity of rock quality in different directions. The suggested method is used to study the spatial distribution regularity of dam foundation. Specific steps are as follows:Firstly, based on the probability distribution functions and corresponding statistical parameters investigated in field, 3D stochastic discrete fracture networks are randomly generated using the Monte Carlo Method. Secondly, lots of generalized RQDt can be calculated by setting measuring points and measuring lines. Thirdly, the spatial distribution regularity of rock quality in different directions can be described according to the spatial distribution map. The results indicate that the proposed method is valid and useful for describing the spatial distribution regularity of rock mass quality.
2016, 24(2): 252-258.
This paper examines the mechanical behavior of salt rock containing fissure. The uniaxial compressive tests are carried out with a servo-controlled test machine RMT-150B.The effect of discontinuous fissures on strength and deformation of salt rock are analyzed. The discontinuous fissures coalescence the behavior of salt rock and its transfixion mode. The discontinuous fissure extension evolution is mainly divided into two types. The main fissures extended from the initial discontinuous fissures of salt rock specimens are the first type. The second type is that the initial discontinuous fissures of specimens are closed and then new micro-fissures are initiated from other place. They are gathered together and formed the main fissures. At the same time, the secondary fissures grow tardily. The tensile transfixion mode and tension-shear transfixion mode are the main transfixion models for salt rock containing discontinuous fissures. Influenced by their own structure compactness, the paths of fissures coalescence presents obvious zigzag line. Effect of vertical transfixion fissures on deformation modulus of salt rock is larger than that of inclined crack.
This paper examines the mechanical behavior of salt rock containing fissure. The uniaxial compressive tests are carried out with a servo-controlled test machine RMT-150B.The effect of discontinuous fissures on strength and deformation of salt rock are analyzed. The discontinuous fissures coalescence the behavior of salt rock and its transfixion mode. The discontinuous fissure extension evolution is mainly divided into two types. The main fissures extended from the initial discontinuous fissures of salt rock specimens are the first type. The second type is that the initial discontinuous fissures of specimens are closed and then new micro-fissures are initiated from other place. They are gathered together and formed the main fissures. At the same time, the secondary fissures grow tardily. The tensile transfixion mode and tension-shear transfixion mode are the main transfixion models for salt rock containing discontinuous fissures. Influenced by their own structure compactness, the paths of fissures coalescence presents obvious zigzag line. Effect of vertical transfixion fissures on deformation modulus of salt rock is larger than that of inclined crack.
2016, 24(2): 259-267.
Saturated-unsaturated state is a natural state of soils. Hence, unsaturated soil mechanics has wide applications in seepage analysis of earth and rockfill dam, contaminant transport, seepage and phase transform of frozen soil, and stability analysis of slope and embankment. As a fundamental relationship, the soil-water characteristic curve(SWCC)plays an essential role in the research of unsaturated soil mechanics. Python language is employed to develop the unsaturated seepage and stability analysis(USSA)software as well as the graphic user interface(GUI)for data processing and data fitting of SWCC curve. Based on a practical slope example, the whole analyzing process is described in details. It is from the data processing and data fitting of SWCC curve to unsaturated seepage analysis and stability analysis. The stability of dam under unsaturated seepage is conducted using the fitted parameters of SWCC model. The numerical results show that the stability evolutions of two dam slopes are quite different under the changing process of water level. When applying the shear strength reduction finite element method to the slope stability of unsaturated soil, the final FOS appears to be the lowest envelope of those FOS curves of all slopes.
Saturated-unsaturated state is a natural state of soils. Hence, unsaturated soil mechanics has wide applications in seepage analysis of earth and rockfill dam, contaminant transport, seepage and phase transform of frozen soil, and stability analysis of slope and embankment. As a fundamental relationship, the soil-water characteristic curve(SWCC)plays an essential role in the research of unsaturated soil mechanics. Python language is employed to develop the unsaturated seepage and stability analysis(USSA)software as well as the graphic user interface(GUI)for data processing and data fitting of SWCC curve. Based on a practical slope example, the whole analyzing process is described in details. It is from the data processing and data fitting of SWCC curve to unsaturated seepage analysis and stability analysis. The stability of dam under unsaturated seepage is conducted using the fitted parameters of SWCC model. The numerical results show that the stability evolutions of two dam slopes are quite different under the changing process of water level. When applying the shear strength reduction finite element method to the slope stability of unsaturated soil, the final FOS appears to be the lowest envelope of those FOS curves of all slopes.
2016, 24(2): 268-275.
A series of water-retention tests are carried out with different net confining pressures by the modified GDS unsaturated soil testing equipment. The deformation behaviour and water-retention characteristic of Xiashu loess are analyzed. Based on the data fitting for the soil-water retention curve of Xiashu loess with the van genuchten model, the influence of net confining pressure on the suction-stress characteristic curve(SSCC) of Xiashu loess is presented. The hydro-mechanical behaviour of Nanjing Xiashu loess in desorption moisture state is systematically studied. The experimental results show that net confining pressure and matric suction have significant influence on the deformation behaviour of Xiashu loess. When the matric suction of Xiashu loess becomes higher, the compressibility tends to be lower. The binary exponential function model is put forward to forecast the exterior relations between void ratio and stress state variables. The distinctness of water-retention characteristics of Xiashu loess follows net confining pressure rise. The power function between air-entry value and net confining pressure is reached. Net confining pressure influences the water-retention characteristic of higer compressive soil more significantly. With the increase of net confining pressure, the void ratio of Xiashu loess proceeds a convergence, and the influence of net confining pressure on the water-retention characteristic has started to decline in due process. The external load on Xiashu loess affects the SSCCs piecewise. In the boundary-effect zone, with the increase of net confining pressure, the difference between SSCCs decreases gradually. In the transition zone, the variations of the differential coefficient of suction stress with the state variables is isolated from the external load. Physical meaning and calculation method of suction stress function at high suctions acquired from theory of electrical double layer are approached. The effective boundary saturation degree is proposed as the demarcation point of suction stress function.
A series of water-retention tests are carried out with different net confining pressures by the modified GDS unsaturated soil testing equipment. The deformation behaviour and water-retention characteristic of Xiashu loess are analyzed. Based on the data fitting for the soil-water retention curve of Xiashu loess with the van genuchten model, the influence of net confining pressure on the suction-stress characteristic curve(SSCC) of Xiashu loess is presented. The hydro-mechanical behaviour of Nanjing Xiashu loess in desorption moisture state is systematically studied. The experimental results show that net confining pressure and matric suction have significant influence on the deformation behaviour of Xiashu loess. When the matric suction of Xiashu loess becomes higher, the compressibility tends to be lower. The binary exponential function model is put forward to forecast the exterior relations between void ratio and stress state variables. The distinctness of water-retention characteristics of Xiashu loess follows net confining pressure rise. The power function between air-entry value and net confining pressure is reached. Net confining pressure influences the water-retention characteristic of higer compressive soil more significantly. With the increase of net confining pressure, the void ratio of Xiashu loess proceeds a convergence, and the influence of net confining pressure on the water-retention characteristic has started to decline in due process. The external load on Xiashu loess affects the SSCCs piecewise. In the boundary-effect zone, with the increase of net confining pressure, the difference between SSCCs decreases gradually. In the transition zone, the variations of the differential coefficient of suction stress with the state variables is isolated from the external load. Physical meaning and calculation method of suction stress function at high suctions acquired from theory of electrical double layer are approached. The effective boundary saturation degree is proposed as the demarcation point of suction stress function.
2016, 24(2): 276-283.
This paper examines the influence of dry density and initial moisture content to the remolded loess permeability. It carries out the permeability test of Malan remolded loess in I phase project of Yan'an New District. The results show that under non-saturation conditions, the time that samples take to get saturated getting longer with the increase of dry density. So the dry density influence on penetration time is most significant, but the initial moisture content is not obvious. Remolded Malan loess permeability coefficient decreases with the increase of initial water content and dry density and gradually tends to stabilize. The relationship between them can be fitted to a power function. Within a certain scope around dry density, the permeability coefficient decreases with the initial water content. Their relation curve can be coupled to a linear equation. The permeability coefficient reduces with the decrease of the void ratio. Moreover, there has a power function relationship between them. The initial moisture content, dry density and void ratio are important factors affecting the permeability of remodeling loess, which has a great influence on the micro-structure of the sample, and leads to the influences to its permeability. This study has many theoretical guidance and practical application value for the engineering construction of Yan'an New District.
This paper examines the influence of dry density and initial moisture content to the remolded loess permeability. It carries out the permeability test of Malan remolded loess in I phase project of Yan'an New District. The results show that under non-saturation conditions, the time that samples take to get saturated getting longer with the increase of dry density. So the dry density influence on penetration time is most significant, but the initial moisture content is not obvious. Remolded Malan loess permeability coefficient decreases with the increase of initial water content and dry density and gradually tends to stabilize. The relationship between them can be fitted to a power function. Within a certain scope around dry density, the permeability coefficient decreases with the initial water content. Their relation curve can be coupled to a linear equation. The permeability coefficient reduces with the decrease of the void ratio. Moreover, there has a power function relationship between them. The initial moisture content, dry density and void ratio are important factors affecting the permeability of remodeling loess, which has a great influence on the micro-structure of the sample, and leads to the influences to its permeability. This study has many theoretical guidance and practical application value for the engineering construction of Yan'an New District.
2016, 24(2): 284-291.
Bohai rock samples have been studied in order to speed up oil and gas resource exploitation in Bohai and improve the existing theory system of rock damage constitutive models. According to the test result parameters, a new damage constitutive model of rock is established. Firstly, with the test of variable temperature and confining pressure of rock specimens in the tri-axis test instrument, the whole stress-strain curves of rock samples are obtained. The Poisson's ratio, elastic modulus and maximum differential stress of the rock are calculated. Secondly, using the graphic method for Mohr stress circle, the cohesive force and internal friction angle of rock samples are determined. Lastly, according to parts of the test data, a new damage constitutive model of rock has been built. The model refers fewer parameters and simple calculation. The calculation results of the model and the whole stress-strain curves of test have verified the accuracy of this rock damage constitutive model. The conclusions of the study can provide experimental and theoretical support to improve the rock damage model and the efficient exploitation of petroleum resources on site.
Bohai rock samples have been studied in order to speed up oil and gas resource exploitation in Bohai and improve the existing theory system of rock damage constitutive models. According to the test result parameters, a new damage constitutive model of rock is established. Firstly, with the test of variable temperature and confining pressure of rock specimens in the tri-axis test instrument, the whole stress-strain curves of rock samples are obtained. The Poisson's ratio, elastic modulus and maximum differential stress of the rock are calculated. Secondly, using the graphic method for Mohr stress circle, the cohesive force and internal friction angle of rock samples are determined. Lastly, according to parts of the test data, a new damage constitutive model of rock has been built. The model refers fewer parameters and simple calculation. The calculation results of the model and the whole stress-strain curves of test have verified the accuracy of this rock damage constitutive model. The conclusions of the study can provide experimental and theoretical support to improve the rock damage model and the efficient exploitation of petroleum resources on site.
2016, 24(2): 292-298.
The Summer Palace in Beijing is one of the world's cultural heritage protection units. Its Longevity Hill is located within the north portion of the Summer Palace. The Hill stands a series of cultural relics. For protection of Longevity Hill and its cultural relics, this paper investigates the characteristics of the hill and rock properties. It is based on the existed documentations of Longevity Hill's geological origin. It measures the rock occurrence and rebound strength at different exposed locations. The physical and mechanical properties include density, tensile strength, compressive strength, shear strength. They are tested in laboratory. The mineral composition and content ratio of the rock at Longevity Hill are obtained using thin-sections, rays test, and SEM tests. The results of experiments and tests can have significance and application because they are the basis for geological research and stone relic protection of Longevity Hill.
The Summer Palace in Beijing is one of the world's cultural heritage protection units. Its Longevity Hill is located within the north portion of the Summer Palace. The Hill stands a series of cultural relics. For protection of Longevity Hill and its cultural relics, this paper investigates the characteristics of the hill and rock properties. It is based on the existed documentations of Longevity Hill's geological origin. It measures the rock occurrence and rebound strength at different exposed locations. The physical and mechanical properties include density, tensile strength, compressive strength, shear strength. They are tested in laboratory. The mineral composition and content ratio of the rock at Longevity Hill are obtained using thin-sections, rays test, and SEM tests. The results of experiments and tests can have significance and application because they are the basis for geological research and stone relic protection of Longevity Hill.
2016, 24(2): 299-308.
Road surface sinking is a serious hidden risk for safety travelling in city. There is a close relation among road surface sinking, underground cave and sewage pipe linkage in Haitai District of Tianjin Hi-tech Industrial Park. In this paper, a generation mechanism of road surface sinking is studied through site investigation, geological radar detection, pipeline robot endoscopic detection technology, engineering drilling and 3-dimensional geological modeling. Through study, it is proven that the generation mechanism is representative and typical in coastal area. The weak nature(geological) system interacts with artificial(engineering) system under complex control of multiple factors. The pipeline is buried in safe soil. Its lateral and vertical immigration can occur due to natural settlement and compaction. It can cause crack and damage to sewage pipes at the joints, which further makes the underground water above the pipeline leaking into the pipeline. Then caves are formed due to loss of particles of soil. It finally leads to road surface sinking. Accordingly, treatment measures before burying pipeline and after occurrence of road surface sinking are proposed respectively. The focus is to prevent exchange of underground water and sewage water in the pipeline due to damage of pipeline and to avoid loss of soil particles surrounding the pipeline.
Road surface sinking is a serious hidden risk for safety travelling in city. There is a close relation among road surface sinking, underground cave and sewage pipe linkage in Haitai District of Tianjin Hi-tech Industrial Park. In this paper, a generation mechanism of road surface sinking is studied through site investigation, geological radar detection, pipeline robot endoscopic detection technology, engineering drilling and 3-dimensional geological modeling. Through study, it is proven that the generation mechanism is representative and typical in coastal area. The weak nature(geological) system interacts with artificial(engineering) system under complex control of multiple factors. The pipeline is buried in safe soil. Its lateral and vertical immigration can occur due to natural settlement and compaction. It can cause crack and damage to sewage pipes at the joints, which further makes the underground water above the pipeline leaking into the pipeline. Then caves are formed due to loss of particles of soil. It finally leads to road surface sinking. Accordingly, treatment measures before burying pipeline and after occurrence of road surface sinking are proposed respectively. The focus is to prevent exchange of underground water and sewage water in the pipeline due to damage of pipeline and to avoid loss of soil particles surrounding the pipeline.
2016, 24(2): 309-314.
With the accelerating pace of urbanization, more and more building foundations appear in hilly areas of loess plateau. Building foundations can have serious uneven subsidences because of large pore loess and special landform, which can lead to crack, or even collapse of buildings. The crustal stress, water content and foundation sedimentation of loess hilly-gully high-stacked foundation are studied via in-situ monitoring. The changing law of filled foundation's water content with season and the affected depth are analyzed. It is found that there exists a soil arch in high-stacked foundation. The relation between sedimentation and filling depth is concluded. The final sedimentation volume is analyzed and conjectured by the use of three-dimension numerical simulation inversion. The foundation deformation law under the effect of upper construction is predicted which provides reference for similar loess high-stacked engineering design and its deformation calculation.
With the accelerating pace of urbanization, more and more building foundations appear in hilly areas of loess plateau. Building foundations can have serious uneven subsidences because of large pore loess and special landform, which can lead to crack, or even collapse of buildings. The crustal stress, water content and foundation sedimentation of loess hilly-gully high-stacked foundation are studied via in-situ monitoring. The changing law of filled foundation's water content with season and the affected depth are analyzed. It is found that there exists a soil arch in high-stacked foundation. The relation between sedimentation and filling depth is concluded. The final sedimentation volume is analyzed and conjectured by the use of three-dimension numerical simulation inversion. The foundation deformation law under the effect of upper construction is predicted which provides reference for similar loess high-stacked engineering design and its deformation calculation.
2016, 24(2): 315-323.
The content of piles test contains pile integrity testing and bearing capacity testing. Its purpose is to determine parameters and choose proper method and device for piles sinking. It needs to take climate and geological conditions in the area of piles test into consideration. Choosing a suitable detection is important to improve parameter accuracy and reduce cost of piles. Vertical static loading test is a reliable analysis of bearing capacity of piles. The methods of pile integrity testing include analysis of core boring, low strain testing, and high strain testing and ultrasonic transmission method. The accuracy of those methods are affected in testing piles on-sea. Fiber optics detection is simple to operate. The accuracy is high. Fiber optics detection is based on BOTDR and FBG theory. But there is just few engineering cases referring to piles test on-sea with fiber optics detection This paper shows an engineering case on piles test referring to three methods. They are the pile integrity testing, fiber optics detection and high strain testing. The successful pile test states the fiber optics detection as a new method is reliable and high accuracy.
The content of piles test contains pile integrity testing and bearing capacity testing. Its purpose is to determine parameters and choose proper method and device for piles sinking. It needs to take climate and geological conditions in the area of piles test into consideration. Choosing a suitable detection is important to improve parameter accuracy and reduce cost of piles. Vertical static loading test is a reliable analysis of bearing capacity of piles. The methods of pile integrity testing include analysis of core boring, low strain testing, and high strain testing and ultrasonic transmission method. The accuracy of those methods are affected in testing piles on-sea. Fiber optics detection is simple to operate. The accuracy is high. Fiber optics detection is based on BOTDR and FBG theory. But there is just few engineering cases referring to piles test on-sea with fiber optics detection This paper shows an engineering case on piles test referring to three methods. They are the pile integrity testing, fiber optics detection and high strain testing. The successful pile test states the fiber optics detection as a new method is reliable and high accuracy.
2016, 24(2): 324-330.
This paper addresses the limited complex and nonlinear characteristics in earthquake-induced risk pregnant environmental sample data. It puts forward a risk early-warning method for such pregnant environment around underground structure on least squares support vector machine. Around risk early-warning object and parameters in after-earthquake risk pregnant to underground engineering, the risk pregnant environment is expressed and designed with Support Vector Machine, and SVM training mechanism was proposed for risk pregnant environment. Such risk early-warning mold and the component is erected for risk pregnant environment around underground structure on least squares support vector machine, which utilizes structural risk minimization principle and nonlinear mapping feature of SVM, and optimizes the penalty function and kernel function parameters with Genetic Algorithm. The model implicitly expresses the non-linear relationship among the risk pregnant environment and factors. Case study shows such model has an effective small sample learning ability, well fitting and forecasting accuracy, which excels the predicting model with BP nerve network.
This paper addresses the limited complex and nonlinear characteristics in earthquake-induced risk pregnant environmental sample data. It puts forward a risk early-warning method for such pregnant environment around underground structure on least squares support vector machine. Around risk early-warning object and parameters in after-earthquake risk pregnant to underground engineering, the risk pregnant environment is expressed and designed with Support Vector Machine, and SVM training mechanism was proposed for risk pregnant environment. Such risk early-warning mold and the component is erected for risk pregnant environment around underground structure on least squares support vector machine, which utilizes structural risk minimization principle and nonlinear mapping feature of SVM, and optimizes the penalty function and kernel function parameters with Genetic Algorithm. The model implicitly expresses the non-linear relationship among the risk pregnant environment and factors. Case study shows such model has an effective small sample learning ability, well fitting and forecasting accuracy, which excels the predicting model with BP nerve network.
2016, 24(2): 331-338.
Monitoring and theoretical research on cold deep pits were very inadequate in Harbin area, fewer on the foundation pit through the winter season. The statistics and analytical process were conducted on monitoring data of Anbu trade area renovation deep excavation pit in Xiangfang district, Harbin. The results show that:The deformation of support structure in the depth direction was composite, and the space effect was not obvious. Take the 1/2 height of pit depth as dividing line, the horizontal displacement of sun angle was greater than negative angle at the same depth above dividing line; the results was opposite below the dividing line. The Supporting effect of the combination of steel sheet pile and PILES wasn't directly better than only PILES, and the stability of the of soil frost heave effect should be taken into account during excavation process. Generally, this support program was feasible, but there were some damages of PILES,the safety factor should be improved. Some similar projects should improve the safety factor during the support system design. The results provided an important basis for the design and construction of deep foundation in Harbin area.
Monitoring and theoretical research on cold deep pits were very inadequate in Harbin area, fewer on the foundation pit through the winter season. The statistics and analytical process were conducted on monitoring data of Anbu trade area renovation deep excavation pit in Xiangfang district, Harbin. The results show that:The deformation of support structure in the depth direction was composite, and the space effect was not obvious. Take the 1/2 height of pit depth as dividing line, the horizontal displacement of sun angle was greater than negative angle at the same depth above dividing line; the results was opposite below the dividing line. The Supporting effect of the combination of steel sheet pile and PILES wasn't directly better than only PILES, and the stability of the of soil frost heave effect should be taken into account during excavation process. Generally, this support program was feasible, but there were some damages of PILES,the safety factor should be improved. Some similar projects should improve the safety factor during the support system design. The results provided an important basis for the design and construction of deep foundation in Harbin area.
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