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Editor Work2012 Vol. 20, No. 5
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2012, 20(5): 651-656.
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The mineral composition of cohesive soil has a significant impact on its engineering and mechanical properties. There are some sophisticated methods and technology to identify clay minerals. However, the quantitative measurement of clay minerals content in soil is still a question. The paper studies the chemical and mineralogical compositions of red clays in Wuming and Guilin by means of chemical analysis, X-ray diffraction test, Bogue method and K-value method. The results show that Kaolinite, gibbsite, goethite are found in both clays and quartz is additionally found in Guilin red clay. The contents of Kaolinite, gibbsite, goethite(2mm) and goethite(2mm) are respectively equal to 74.0%, 12.53%, 2.22% and 8.37%in Wuming red clay. The contents of Kaolinite, gibbsite, goethite and quartz are respectively 56.59%, 11.44%, 15.61% and 12.45%in Guilin red clay.
The mineral composition of cohesive soil has a significant impact on its engineering and mechanical properties. There are some sophisticated methods and technology to identify clay minerals. However, the quantitative measurement of clay minerals content in soil is still a question. The paper studies the chemical and mineralogical compositions of red clays in Wuming and Guilin by means of chemical analysis, X-ray diffraction test, Bogue method and K-value method. The results show that Kaolinite, gibbsite, goethite are found in both clays and quartz is additionally found in Guilin red clay. The contents of Kaolinite, gibbsite, goethite(2mm) and goethite(2mm) are respectively equal to 74.0%, 12.53%, 2.22% and 8.37%in Wuming red clay. The contents of Kaolinite, gibbsite, goethite and quartz are respectively 56.59%, 11.44%, 15.61% and 12.45%in Guilin red clay.
2012, 20(5): 657-662.
Pre-consolidation pressure is an important parameter which can help civil engineers predict foundation settlement, take preventive measures and finally solve the problem. This paper analyzes applicability of exiting five mathematical models and originally used Gauss1 Gauss2models to determine pre-consolidation pressure of silt clay. It examines the difference between the determined pre-consolidation pressure values with those mathematical models and that with the empirical method of standard for test methods of earthworks. It then suggests how to choose optimal mathematical model to determine pre-consolidation pressure through researched CFSPT by Matlab. It is shown that though seven mathematical models all have a high fitting degree, only the pre-consolidation pressure of Gauss1model approaches that of empirical method. Besides, the optimal mathematical model should have such characters that e-lgp curve converges a constant of nonzero at start, zero at end, and the middle of e-lgp curve converges a skew line.
Pre-consolidation pressure is an important parameter which can help civil engineers predict foundation settlement, take preventive measures and finally solve the problem. This paper analyzes applicability of exiting five mathematical models and originally used Gauss1 Gauss2models to determine pre-consolidation pressure of silt clay. It examines the difference between the determined pre-consolidation pressure values with those mathematical models and that with the empirical method of standard for test methods of earthworks. It then suggests how to choose optimal mathematical model to determine pre-consolidation pressure through researched CFSPT by Matlab. It is shown that though seven mathematical models all have a high fitting degree, only the pre-consolidation pressure of Gauss1model approaches that of empirical method. Besides, the optimal mathematical model should have such characters that e-lgp curve converges a constant of nonzero at start, zero at end, and the middle of e-lgp curve converges a skew line.
2012, 20(5): 663-673.
Upon drying, the evaporation of soil water results in volumetric shrinkage and desiccation cracks on expansive soils. The presence of crack can significantly weaken the engineering properties of soil, and cause various problems in geological, geotechnical, hydraulic, environmental engineering fields. With the increasing frequency of severe drought climate, the engineering problems that induced by desiccation cracking can be more and more, worse and worse. The study of desiccation cracking is therefore very significant for revealing the intrinsic mechanisms behind this common natural phenomenon, and plays an important role in engineering practice in clayey soil areas and especially in expansive soil areas. Generally, the initiation and propagation of desiccation cracks show evident dynamic characteristics and significantly depend on soil water evaporation rate, stress state and shrinkage property. The cracks initiate at constant evaporation rate stage. Soil suction and tensile strength are the two key mechanical parameters that control the cracking behavior. Cracking is likely to occur if the tensile stress which is induced by soil suction reaches the tensile strength of soil. Intrinsically, cracking is the result of pore shrinkage. It is believed that the mechanical effect and shrinkage potential are the two necessary factors for crack initiation. It is found that the desiccation cracking behaviour is affected by many factors including soil materials, mechanical properties, structures, test conditions, and test methods. Quantitative characterization of crack patterns is required for desiccation cracking investigation, and plays very important role in understanding the cracking mechanism and constructing the relevant model. Image processing is a powerful, efficient and high-accurate tool for quantitative description crack patterns. In the next stage, more attention should be paid to the dynamic characteristics of cracking, and more work should be done on water-soil interaction, mechanical mechanism, shrinkage mechanism, large scale field test and 3D quantification technique that related to soil desiccation cracking. It is also important to study desiccation cracking behaviour on the basis of soil materials, mechanics and structures, to integrate macro-observation with micro-analysis and to construct perfect theory for characterizing desiccation cracking.
Upon drying, the evaporation of soil water results in volumetric shrinkage and desiccation cracks on expansive soils. The presence of crack can significantly weaken the engineering properties of soil, and cause various problems in geological, geotechnical, hydraulic, environmental engineering fields. With the increasing frequency of severe drought climate, the engineering problems that induced by desiccation cracking can be more and more, worse and worse. The study of desiccation cracking is therefore very significant for revealing the intrinsic mechanisms behind this common natural phenomenon, and plays an important role in engineering practice in clayey soil areas and especially in expansive soil areas. Generally, the initiation and propagation of desiccation cracks show evident dynamic characteristics and significantly depend on soil water evaporation rate, stress state and shrinkage property. The cracks initiate at constant evaporation rate stage. Soil suction and tensile strength are the two key mechanical parameters that control the cracking behavior. Cracking is likely to occur if the tensile stress which is induced by soil suction reaches the tensile strength of soil. Intrinsically, cracking is the result of pore shrinkage. It is believed that the mechanical effect and shrinkage potential are the two necessary factors for crack initiation. It is found that the desiccation cracking behaviour is affected by many factors including soil materials, mechanical properties, structures, test conditions, and test methods. Quantitative characterization of crack patterns is required for desiccation cracking investigation, and plays very important role in understanding the cracking mechanism and constructing the relevant model. Image processing is a powerful, efficient and high-accurate tool for quantitative description crack patterns. In the next stage, more attention should be paid to the dynamic characteristics of cracking, and more work should be done on water-soil interaction, mechanical mechanism, shrinkage mechanism, large scale field test and 3D quantification technique that related to soil desiccation cracking. It is also important to study desiccation cracking behaviour on the basis of soil materials, mechanics and structures, to integrate macro-observation with micro-analysis and to construct perfect theory for characterizing desiccation cracking.
2012, 20(5): 674-681.
This paper proposes a u-p approximation for the evaluation of pore pressure and effective stresses in porous seabed combined wave and current loadings.The analytical solution of pore pressure and effective stresses is obtained.The effects of currents are considered in this new analytical solution.The new analytical solution is verified by field data and comsol numerical solution respectively.Then,using the analytical solution,a parametric study for the effects of currents is carried out.The paper further explores the effects of currents for various seabed thicknesses and the seabed response under different wave/current cases.Numerical results demonstrate the significant effects of currents and non-linear waves on pore pressure and effective stresses.Finally,the paper studies the effects of current direction on seabed response.The results show that the relative difference of the maximum pore pressure between different direction currents can reach 15% of the static water pressure.Therefore,the effects of currents cannot always be ignored.
This paper proposes a u-p approximation for the evaluation of pore pressure and effective stresses in porous seabed combined wave and current loadings.The analytical solution of pore pressure and effective stresses is obtained.The effects of currents are considered in this new analytical solution.The new analytical solution is verified by field data and comsol numerical solution respectively.Then,using the analytical solution,a parametric study for the effects of currents is carried out.The paper further explores the effects of currents for various seabed thicknesses and the seabed response under different wave/current cases.Numerical results demonstrate the significant effects of currents and non-linear waves on pore pressure and effective stresses.Finally,the paper studies the effects of current direction on seabed response.The results show that the relative difference of the maximum pore pressure between different direction currents can reach 15% of the static water pressure.Therefore,the effects of currents cannot always be ignored.
2012, 20(5): 682-686.
The development of underground space has gone towards deep earth in Beijing City. The importance of the study on Tertiary engineering geology is increasing prominently. The Tertiary engineering geology is weak in contrast to the Quaternary engineering geology in Beijing.Based on the analysis of abundant engineering geological data and according to the general theory of sediment, the Tertiary sediment is discussed systematically from the point of geological structure for the first time. A series of conclusions are deduced. On the basis of the data of borehole and physical mechanical test, the unified engineering geological stratum is further discussed. It is an important support for the planning of the deep underground space in the Center region (with the depth of 100m and area of 336km2) of Beijing City. At the same time, it serves good references for further study on the Tertiary geology, especially Tertiary engineering geology from methodology and idea.
The development of underground space has gone towards deep earth in Beijing City. The importance of the study on Tertiary engineering geology is increasing prominently. The Tertiary engineering geology is weak in contrast to the Quaternary engineering geology in Beijing.Based on the analysis of abundant engineering geological data and according to the general theory of sediment, the Tertiary sediment is discussed systematically from the point of geological structure for the first time. A series of conclusions are deduced. On the basis of the data of borehole and physical mechanical test, the unified engineering geological stratum is further discussed. It is an important support for the planning of the deep underground space in the Center region (with the depth of 100m and area of 336km2) of Beijing City. At the same time, it serves good references for further study on the Tertiary geology, especially Tertiary engineering geology from methodology and idea.
2012, 20(5): 687-692.
Heap(or talus) refers to the accumulation of loose material lies in hillside toe or gentle slope that rock materials are handled by gravity. The proposed appropriate highway route schemes through many large broken rock debris stockpiles(or heaps).The geological conditions are complicated. The compaction degrees of rock piled masses everywhere are also not identical. The strength and stability of different compaction degrees of rock debris piled masses are different greatly. They have huge disadvantages to the project construction. For this reason, experiments of large direct shear strength characteristics of rock debris piled masses with same water content and different densities are carried out. The result shows the follows. The evenness of heap mass moisture contents and densities are very poor. The rock heap filling and cementing content moisture are about 5%~7%.The average water content is 6.5%.The maximum of dry density is 2.25gcm-3.The average of natural density is 2.11gcm-3.The average of dry density is 1.98gcm-3.The samples in low vertical pressure(50, 100, 200kPa) appear the shear stress peaks 116, 154 and 211kPa respectively when the dry density is 2.10g cm-3.The other results show that the shear stress increases with the shear displacement, has no clear peak, and displays strain hardening characteristics obviously. The parameters of rock mass' direct shear strength(c and )increase with the dried density. The general rock heap mass with the same water content is more reinforced when the shear strength is higher. The sensitivity of shear strength to compactness falls drastically with the increase of rock heap mass density in the original gradation and different dry densities.
Heap(or talus) refers to the accumulation of loose material lies in hillside toe or gentle slope that rock materials are handled by gravity. The proposed appropriate highway route schemes through many large broken rock debris stockpiles(or heaps).The geological conditions are complicated. The compaction degrees of rock piled masses everywhere are also not identical. The strength and stability of different compaction degrees of rock debris piled masses are different greatly. They have huge disadvantages to the project construction. For this reason, experiments of large direct shear strength characteristics of rock debris piled masses with same water content and different densities are carried out. The result shows the follows. The evenness of heap mass moisture contents and densities are very poor. The rock heap filling and cementing content moisture are about 5%~7%.The average water content is 6.5%.The maximum of dry density is 2.25gcm-3.The average of natural density is 2.11gcm-3.The average of dry density is 1.98gcm-3.The samples in low vertical pressure(50, 100, 200kPa) appear the shear stress peaks 116, 154 and 211kPa respectively when the dry density is 2.10g cm-3.The other results show that the shear stress increases with the shear displacement, has no clear peak, and displays strain hardening characteristics obviously. The parameters of rock mass' direct shear strength(c and )increase with the dried density. The general rock heap mass with the same water content is more reinforced when the shear strength is higher. The sensitivity of shear strength to compactness falls drastically with the increase of rock heap mass density in the original gradation and different dry densities.
2012, 20(5): 693-699.
It is known that investigating the failure pattern is important for the design and construction monitoring of reinforced soil slope. In this paper, reinforced soil slopes with different reinforcements and soils are studied using centrifuge modeling. During the modeling, failure patterns are drawn and compared. Results show that the reinforced soil slopes are generally able to maintain better integrity and are not likely to collapse suddenly. Cracks may first occur near the slope surface. Therefore, significant cracks on the top of the slope may always imply that hidden cracks near the slope surface have also occurred. Generally, larger reinforcement modulus can bring better reinforcing effect. However, if the strength of the interface cannot be improved appropriately, it can be useless to indefinitely increase the modulus of the reinforcement once it is large enough.
It is known that investigating the failure pattern is important for the design and construction monitoring of reinforced soil slope. In this paper, reinforced soil slopes with different reinforcements and soils are studied using centrifuge modeling. During the modeling, failure patterns are drawn and compared. Results show that the reinforced soil slopes are generally able to maintain better integrity and are not likely to collapse suddenly. Cracks may first occur near the slope surface. Therefore, significant cracks on the top of the slope may always imply that hidden cracks near the slope surface have also occurred. Generally, larger reinforcement modulus can bring better reinforcing effect. However, if the strength of the interface cannot be improved appropriately, it can be useless to indefinitely increase the modulus of the reinforcement once it is large enough.
2012, 20(5): 700-705.
Fault movement cannot only cause earthquake, but also bring about permanent deformation in strata. They have great damage to structures, especially linear structures like underground pipelines and tunnels unavoidably. The Kobe earthquake in Japan in 1995 and the Taiwan Chi-Chi earthquake in 1999,the WenChuan earthquake in China in 2008 have all caused to large losses of lives and properties. Active faults are widely distributed in China. Therefore, study on earthquake fault rupture propagation in overlying strata is essential. Many scholars at home and abroad have paid attentions to this subject. Modeling test, centrifuge test and numerical method are used to research the problem. Generally the damages induced by surface rupture are considered as a result of discontinuous deformations of overlying soil resulting in vertical or lateral offset at the surface of soil. However, due to the reason of the complexity of geological and stratigraphic conditions, the limitation of research and field monitoring methods, the question still does not have a clear answer.
On the base of sand box, the paper aims to reveal the patterns of fault rupture propagation and location of surface rupture in sandy soil under 1-g modeling test of normal fault. It also studies the relationship between vertical displacement and height of overlying strata.that the following results are found. The failure surfaces of normal fault begin to propagate directly up to the surface regardless to dip angle. Then the following failure surfaces appear. The required vertical displacement when a complete failure surface forms is independent with the dip angle. In the modeling test, the value of D/H comes out to be 4.4%.As many failure planes exist when fault rupture propagates, an apparent triangle shear zone stays between them. At the surface, the width of the triangle shear zone reaches a maximum S.The value of S becomes greater as the dip angle decreases.
Fault movement cannot only cause earthquake, but also bring about permanent deformation in strata. They have great damage to structures, especially linear structures like underground pipelines and tunnels unavoidably. The Kobe earthquake in Japan in 1995 and the Taiwan Chi-Chi earthquake in 1999,the WenChuan earthquake in China in 2008 have all caused to large losses of lives and properties. Active faults are widely distributed in China. Therefore, study on earthquake fault rupture propagation in overlying strata is essential. Many scholars at home and abroad have paid attentions to this subject. Modeling test, centrifuge test and numerical method are used to research the problem. Generally the damages induced by surface rupture are considered as a result of discontinuous deformations of overlying soil resulting in vertical or lateral offset at the surface of soil. However, due to the reason of the complexity of geological and stratigraphic conditions, the limitation of research and field monitoring methods, the question still does not have a clear answer.
On the base of sand box, the paper aims to reveal the patterns of fault rupture propagation and location of surface rupture in sandy soil under 1-g modeling test of normal fault. It also studies the relationship between vertical displacement and height of overlying strata.that the following results are found. The failure surfaces of normal fault begin to propagate directly up to the surface regardless to dip angle. Then the following failure surfaces appear. The required vertical displacement when a complete failure surface forms is independent with the dip angle. In the modeling test, the value of D/H comes out to be 4.4%.As many failure planes exist when fault rupture propagates, an apparent triangle shear zone stays between them. At the surface, the width of the triangle shear zone reaches a maximum S.The value of S becomes greater as the dip angle decreases.
2012, 20(5): 706-714.
This paper presents a case study on the weathering rate of pelitic siltstone as the surrounding rock of Longyou underground caverns. The chisel imprints on the inner surface of the surrounding rock were measured using the mixture of plasticene and additives in 2004, 2008 and 2012,respectively. The maximum height difference and fluctuation ratio are adopted as the quantitative indexes to describe the shapes of the chisel imprints. According to the measured results, the weathering rate of the surrounding rock is calculated. The average weathering rate is about 0.28 to 0.5mma-1.The maximum weathering rate is about 0.46~0.89mma-1.The weathering rate value in the last 4 years is smaller than that in the former 4 years. Under the micro-environment, the weathering time limit of the 5 caverns is about 30 years, which means the chisel imprints would be vanished within 100 years. Protective measures should be carried out as fast as possible. The research results can provide scientific supports for the protection of Longyou Caverns, scientific and reasonable development of national cultural relics and reduce of management risks.
This paper presents a case study on the weathering rate of pelitic siltstone as the surrounding rock of Longyou underground caverns. The chisel imprints on the inner surface of the surrounding rock were measured using the mixture of plasticene and additives in 2004, 2008 and 2012,respectively. The maximum height difference and fluctuation ratio are adopted as the quantitative indexes to describe the shapes of the chisel imprints. According to the measured results, the weathering rate of the surrounding rock is calculated. The average weathering rate is about 0.28 to 0.5mma-1.The maximum weathering rate is about 0.46~0.89mma-1.The weathering rate value in the last 4 years is smaller than that in the former 4 years. Under the micro-environment, the weathering time limit of the 5 caverns is about 30 years, which means the chisel imprints would be vanished within 100 years. Protective measures should be carried out as fast as possible. The research results can provide scientific supports for the protection of Longyou Caverns, scientific and reasonable development of national cultural relics and reduce of management risks.
2012, 20(5): 715-722.
This paper examines the tectonic stress field in the Longmenshan region where the Wenchuan 8.0 earthquake occurred in 2008.The evolution of tectonic stress field before-,during-and after-earthquake is studied with numerical modelling. It is found that from the time before main shock to the time after main shock, the regional stress field experienced complex change process. The magnitudes and orientations of principal stresses and shear stresses changed a great deal. The changes coincide well with the deformation caused by the earthquake and the distribution of the after-shocks.
This paper examines the tectonic stress field in the Longmenshan region where the Wenchuan 8.0 earthquake occurred in 2008.The evolution of tectonic stress field before-,during-and after-earthquake is studied with numerical modelling. It is found that from the time before main shock to the time after main shock, the regional stress field experienced complex change process. The magnitudes and orientations of principal stresses and shear stresses changed a great deal. The changes coincide well with the deformation caused by the earthquake and the distribution of the after-shocks.
2012, 20(5): 723-731.
The failure of some high fill slopes in recent years has caused serious after-effects to the safety of mountain airports. This paper takes the No.12 landslide of high fill slopes in Panzhihua airport as an example to discuss the sliding mechanism and the reinforced countermeasures of a high fill slope in mountain airport. The geological background and basic features of the No.12 landslide in the high fill slopes and its pretreatment schemes are described. The phenomena and process of deformation and failure for the landslide are also introduced in detail. The analysis of formation conditions and influence factors as well as the numerical modeling has revealed the formation mechanism and evolution process of No.12 landslide. Research results show that the main reasons resulted in the landslide are the soft mudstone layer in the bottom of fill slope, the abundant groundwater in the fill slope, the unreasonable layout of pre-reinforcement piles and the inducement of storm rainfall. The mode of the formation mechanism of the No.12 landslide is summarized as push creepinglocking and progressive shearingbreak sliding and overlapping.
The failure of some high fill slopes in recent years has caused serious after-effects to the safety of mountain airports. This paper takes the No.12 landslide of high fill slopes in Panzhihua airport as an example to discuss the sliding mechanism and the reinforced countermeasures of a high fill slope in mountain airport. The geological background and basic features of the No.12 landslide in the high fill slopes and its pretreatment schemes are described. The phenomena and process of deformation and failure for the landslide are also introduced in detail. The analysis of formation conditions and influence factors as well as the numerical modeling has revealed the formation mechanism and evolution process of No.12 landslide. Research results show that the main reasons resulted in the landslide are the soft mudstone layer in the bottom of fill slope, the abundant groundwater in the fill slope, the unreasonable layout of pre-reinforcement piles and the inducement of storm rainfall. The mode of the formation mechanism of the No.12 landslide is summarized as push creepinglocking and progressive shearingbreak sliding and overlapping.
2012, 20(5): 732-744.
Many landslides were triggered by Haiti Earthquake(Mw 7.0) of January 12, 2010.Base on Geographic Information Systems(GIS) and remote sensing technologies, three detailed landslide inventories were constructed. The three inventories are respectively landslide polygons, landside centroid points, and landslide top points. It is indicated that 30, 828 landslides triggered by the Haiti earthquake throughout the site with area of 3, 192.85km2.These landslides cover a total area of 15.736km2.Correlations of landslide occurrence with seismic parameters, topographic conditions and distance from roads are analyzed using the three landslide inventories. Statistical analysis of these landslides spatial distribution is carried out with four indices. They are a) landslide centroid number density(LCND),defined as the number of landslide centroid per square kilometer, b)landslide top number density(LTND),defined as the number of landslide top point per square kilometer, c)landslide area percentage(LAP),defined as the percentage of the area affected by the landslides, and d) landslide erosion thickness(LET),defined as the landslide material thickness per square kilometer. It is to determine how the occurrence of landslides and their erosion thickness correlates with seismic parameters, topographic conditions and distance from roads. It is observed that values of four indices(LCND,LTND,LAP and LET)have generally positive correlations with slope angle and peak ground acceleration(PGA), and have generally negative correlations with distance from the Enriquillo-Plantain Garden fault, and distance from drainages. Statistical results of landslide and their erosion thickness with distance along the Enriquillo-Plantain Garden fault show that areas from 22 to 26km and 8 to 12km, western of the epicenter, and from 6 to 18km, eastern of the epicenter are landslide high susceptibility areas. It also represents more slope curvature close to zero, more difficult to earthquake triggered landslide occurrence. The highest values appear at range from 200m to 1200m in elevation. The landslides have preferred orientation dominated by the eastern. No apparent correlations were found in the LCND,LTND,LAP and LET values with distance from epicenter and distance from roads.
Many landslides were triggered by Haiti Earthquake(Mw 7.0) of January 12, 2010.Base on Geographic Information Systems(GIS) and remote sensing technologies, three detailed landslide inventories were constructed. The three inventories are respectively landslide polygons, landside centroid points, and landslide top points. It is indicated that 30, 828 landslides triggered by the Haiti earthquake throughout the site with area of 3, 192.85km2.These landslides cover a total area of 15.736km2.Correlations of landslide occurrence with seismic parameters, topographic conditions and distance from roads are analyzed using the three landslide inventories. Statistical analysis of these landslides spatial distribution is carried out with four indices. They are a) landslide centroid number density(LCND),defined as the number of landslide centroid per square kilometer, b)landslide top number density(LTND),defined as the number of landslide top point per square kilometer, c)landslide area percentage(LAP),defined as the percentage of the area affected by the landslides, and d) landslide erosion thickness(LET),defined as the landslide material thickness per square kilometer. It is to determine how the occurrence of landslides and their erosion thickness correlates with seismic parameters, topographic conditions and distance from roads. It is observed that values of four indices(LCND,LTND,LAP and LET)have generally positive correlations with slope angle and peak ground acceleration(PGA), and have generally negative correlations with distance from the Enriquillo-Plantain Garden fault, and distance from drainages. Statistical results of landslide and their erosion thickness with distance along the Enriquillo-Plantain Garden fault show that areas from 22 to 26km and 8 to 12km, western of the epicenter, and from 6 to 18km, eastern of the epicenter are landslide high susceptibility areas. It also represents more slope curvature close to zero, more difficult to earthquake triggered landslide occurrence. The highest values appear at range from 200m to 1200m in elevation. The landslides have preferred orientation dominated by the eastern. No apparent correlations were found in the LCND,LTND,LAP and LET values with distance from epicenter and distance from roads.
2012, 20(5): 745-750.
The occurrences of landslides usually have a good relationship with rainfall, especially with extreme rainfall events. Based on the theory of Gumbel Extreme Distribution, rainfall precipitation of Badong county in the Three Gorges Reservoir from 1990 to 2006 was statistically analyzed in the paper. Some special extreme values and distribution curves for rainfalls in flood seasons were obtained, including the maximum accumulative daily rainfall, the greatest accumulation rainfall. It is concluded that: with the increase of return period, the accumulation rainfall of one rainfall course can increase; with the increase of rainy days, the accumulation rainfall of one rainfall event with different return period can increase. And longer the return period is,greater the rainfall can be. Based on the above conclusions, the results are respectively used to re-active and newly active landslides trigged by rainfall. The method of probability of the landslide is further discussed in this paper.
The occurrences of landslides usually have a good relationship with rainfall, especially with extreme rainfall events. Based on the theory of Gumbel Extreme Distribution, rainfall precipitation of Badong county in the Three Gorges Reservoir from 1990 to 2006 was statistically analyzed in the paper. Some special extreme values and distribution curves for rainfalls in flood seasons were obtained, including the maximum accumulative daily rainfall, the greatest accumulation rainfall. It is concluded that: with the increase of return period, the accumulation rainfall of one rainfall course can increase; with the increase of rainy days, the accumulation rainfall of one rainfall event with different return period can increase. And longer the return period is,greater the rainfall can be. Based on the above conclusions, the results are respectively used to re-active and newly active landslides trigged by rainfall. The method of probability of the landslide is further discussed in this paper.
2012, 20(5): 751-759.
The analysis of earthquake stability of slopes is one of the most important research subjects in geotechnical engineering and earthquake engineering. Two different concepts of slope earthquake stability are put forward in this paper. One concept is the so-called strength reserve stability which can be figured out by comparison of present strength of a slope to its critical strength that is degenerated from its present strength till to the dynamic failure of the slope under the earthquake action of a certain intensity. The other is named as the dynamic overloading stability which can be evaluated by contrast between the actual earthquake action that just makes a slope damaged and the earthquake action as the local antiseismic precautionary standard. The first concept of slope earthquake stability has been widely accepted. Its relative analysis methods are also well developed. The second one, however, is seldom mentioned till now. Its failure criterion and analysis method are yet to be explored. This paper investigates the failure criterion and the analysis method of dynamic overloading earthquake stability. The criteria of the critical earthquake peak acceleration for the dynamic overloading stability of a slope and its analysis method, and the load increasing method are put forward. During the analysis process, the action of earthquake force begins from a lower level and gradually increases to the critical intensity that just makes the current strength slope reach the state of dynamic failure. The earthquake stability of the slope is determined by the comparison of the critical earthquake peak acceleration and the antiseismic precautionary earthquake peak acceleration on the field of the slope. The dynamic overloading earthquake stability of a loess slope at Panlongyuan in Baoji, Shaanxi Province, China is analyzed with the load increasing method proposed in this paper. The analysis result reveals that the dynamic overloading earthquake stability of the slope is quite high to the action of the earthquake ground motion with exceeding probability 10%in coming 50 years.
The analysis of earthquake stability of slopes is one of the most important research subjects in geotechnical engineering and earthquake engineering. Two different concepts of slope earthquake stability are put forward in this paper. One concept is the so-called strength reserve stability which can be figured out by comparison of present strength of a slope to its critical strength that is degenerated from its present strength till to the dynamic failure of the slope under the earthquake action of a certain intensity. The other is named as the dynamic overloading stability which can be evaluated by contrast between the actual earthquake action that just makes a slope damaged and the earthquake action as the local antiseismic precautionary standard. The first concept of slope earthquake stability has been widely accepted. Its relative analysis methods are also well developed. The second one, however, is seldom mentioned till now. Its failure criterion and analysis method are yet to be explored. This paper investigates the failure criterion and the analysis method of dynamic overloading earthquake stability. The criteria of the critical earthquake peak acceleration for the dynamic overloading stability of a slope and its analysis method, and the load increasing method are put forward. During the analysis process, the action of earthquake force begins from a lower level and gradually increases to the critical intensity that just makes the current strength slope reach the state of dynamic failure. The earthquake stability of the slope is determined by the comparison of the critical earthquake peak acceleration and the antiseismic precautionary earthquake peak acceleration on the field of the slope. The dynamic overloading earthquake stability of a loess slope at Panlongyuan in Baoji, Shaanxi Province, China is analyzed with the load increasing method proposed in this paper. The analysis result reveals that the dynamic overloading earthquake stability of the slope is quite high to the action of the earthquake ground motion with exceeding probability 10%in coming 50 years.
2012, 20(5): 760-767.
A small local failure block in surrounding slope of hydropower project can become a big potential hazard for hydraulic construction(structure) building and human security. So the assessment of surrounding slope has to pay more attention to the stability investigation and assessment of the local and small block. There are a total of 100 hazard sources existing in surrounding slope of Busigou hydropower project.61 of them are developed in the left bank and 39 in the right bank. Based on a large number of precise field investigation and analysis, a classification is proposed according to geological genesis, scale and failure mechanism respectively. According to geological genesis, hazard sources are divided into four types: (group of )isolated stone,(group of )dangerous rock(generally100m3),dangerous rock mass and high position covering layer. Considering the hazard stability and degree of project importance, hazard rating assessment system(HRAS) of surrounding slope which has enough easily valued indicators is established according to three first level indicators(the hazard source, path and inducing factors),nine secondary indicators(stability, potential energy, hazard sources' shape, path's geometric features, vegetation growth, earthquake and rainfall), and 35 basic indicators. According to the level of values, hazard rating is divided into three levelshigh, medium, and low level. Using this assessment system to evaluate the hazard rating of surrounding slope of Busigou hydropower project, the evaluation results show that in the total of 100 hazard sources,19 are of high hazard rating, 55 of medium and 26 of low hazard sources. The result is largely correspondence to reality. This assessment system has some engineering significance for hazard source prevention and controlling.
A small local failure block in surrounding slope of hydropower project can become a big potential hazard for hydraulic construction(structure) building and human security. So the assessment of surrounding slope has to pay more attention to the stability investigation and assessment of the local and small block. There are a total of 100 hazard sources existing in surrounding slope of Busigou hydropower project.61 of them are developed in the left bank and 39 in the right bank. Based on a large number of precise field investigation and analysis, a classification is proposed according to geological genesis, scale and failure mechanism respectively. According to geological genesis, hazard sources are divided into four types: (group of )isolated stone,(group of )dangerous rock(generally100m3),dangerous rock mass and high position covering layer. Considering the hazard stability and degree of project importance, hazard rating assessment system(HRAS) of surrounding slope which has enough easily valued indicators is established according to three first level indicators(the hazard source, path and inducing factors),nine secondary indicators(stability, potential energy, hazard sources' shape, path's geometric features, vegetation growth, earthquake and rainfall), and 35 basic indicators. According to the level of values, hazard rating is divided into three levelshigh, medium, and low level. Using this assessment system to evaluate the hazard rating of surrounding slope of Busigou hydropower project, the evaluation results show that in the total of 100 hazard sources,19 are of high hazard rating, 55 of medium and 26 of low hazard sources. The result is largely correspondence to reality. This assessment system has some engineering significance for hazard source prevention and controlling.
2012, 20(5): 768-773.
Jinsha Jiang Bridge is located in the deep gorge of the Jinsha River Tiger Leaping Gorge town, a high seismic intensity area. The rock slope at left of the bridge and on the side of Shangri-La City is affected by terrain steep unloading fractures. It is importance to study the slope rock stability in loads of engineering. According to the engineering geological conditions and the characteristics of joints, Barton model and shear stress test, strength parameters of rock mass structure surface are discussed. Then, the failure trend in gravity and engineering are analyzed by bottom friction test. In order to evaluate the damage trends of the rock mass under the different loading conditions such gravity, bridge loading and seismic load, a calculation model based on the geological model and slope stability is simulated and analyzed using Discrete Element Method(DEM).The numerical analysis results indicate the effect of degradation of discontinuities on the slope stability. The results have shown that the destruction of rock mass under the gravity and bridge foundation is mainly concentrated within 30m depth of the slope. The slope under loading may cause loosening strength along joint planes. But under earthquake and bridge loads, bridge foundation should be strengthened.
Jinsha Jiang Bridge is located in the deep gorge of the Jinsha River Tiger Leaping Gorge town, a high seismic intensity area. The rock slope at left of the bridge and on the side of Shangri-La City is affected by terrain steep unloading fractures. It is importance to study the slope rock stability in loads of engineering. According to the engineering geological conditions and the characteristics of joints, Barton model and shear stress test, strength parameters of rock mass structure surface are discussed. Then, the failure trend in gravity and engineering are analyzed by bottom friction test. In order to evaluate the damage trends of the rock mass under the different loading conditions such gravity, bridge loading and seismic load, a calculation model based on the geological model and slope stability is simulated and analyzed using Discrete Element Method(DEM).The numerical analysis results indicate the effect of degradation of discontinuities on the slope stability. The results have shown that the destruction of rock mass under the gravity and bridge foundation is mainly concentrated within 30m depth of the slope. The slope under loading may cause loosening strength along joint planes. But under earthquake and bridge loads, bridge foundation should be strengthened.
2012, 20(5): 774-780.
The Tiantaixiang landslide is one of the typical gently dipping translational rock slides forming in the red beds in east Sichuan province. In order to discover the mechanism of these landslides, the slip zone behavior of Tiantaixiang landslide is studied in detail. Physical property tests show that the slip zone soil is plastic silty clay. The X-ray diffraction analysis reveals that the main mineral components of the slip zone are composed of chlorite, illite, feldspar, quartz and calcite. The results of scanning electron micrograph display that the microstructures of the slip zone are mainly sheet crystals and directional crystal structures, and micro pores developed well. Consolidated slow direct shear tests are conducted on the slip zone specimens. The results are c=9.2~10.7kPa and ＝10.4~12.3.Triaxial consolidated drained creep tests are conducted on the slip zone specimens to obtain the creep strength. The results show that the creep strength are c=18.1kPa and ＝8.0.The large amount of chlorite and illite in the slip zone resulting in low shear strength and low creep strength is the main inner factor contributing to the sliding.
The Tiantaixiang landslide is one of the typical gently dipping translational rock slides forming in the red beds in east Sichuan province. In order to discover the mechanism of these landslides, the slip zone behavior of Tiantaixiang landslide is studied in detail. Physical property tests show that the slip zone soil is plastic silty clay. The X-ray diffraction analysis reveals that the main mineral components of the slip zone are composed of chlorite, illite, feldspar, quartz and calcite. The results of scanning electron micrograph display that the microstructures of the slip zone are mainly sheet crystals and directional crystal structures, and micro pores developed well. Consolidated slow direct shear tests are conducted on the slip zone specimens. The results are c=9.2~10.7kPa and ＝10.4~12.3.Triaxial consolidated drained creep tests are conducted on the slip zone specimens to obtain the creep strength. The results show that the creep strength are c=18.1kPa and ＝8.0.The large amount of chlorite and illite in the slip zone resulting in low shear strength and low creep strength is the main inner factor contributing to the sliding.
2012, 20(5): 781-788.
This paper studies a landslide at a large coal mine site in Shanxi province. The effect of underground mining on the stability of the old landslide and the reactivation mechanism are analyzed. The mining displacement can greatly reduce the strength of the soil. The tensile cracks can provide infiltration path for surface water which can reduce the physical and mechanical properties of the soil of sliding zone. The gob movement and deformation in the front of landslide play a dragging role in the damage of the landslide. The boundaries and the sliding surface of the landslide have been determined by the ways of engineering geological mapping, drilling, geophysical investigation and deformation monitoring. The landslide is zoned based on the topography, material composition and deformation characters. The mitigation measures of ordered retaining structures in the landslide and anti-sliding pillar in the mine have been carried out according to the deformation characteristics, geological and environmental conditions and mining demand. Monitoring data show that the landslide keeps stable as the mitigation measure putting into effect.
This paper studies a landslide at a large coal mine site in Shanxi province. The effect of underground mining on the stability of the old landslide and the reactivation mechanism are analyzed. The mining displacement can greatly reduce the strength of the soil. The tensile cracks can provide infiltration path for surface water which can reduce the physical and mechanical properties of the soil of sliding zone. The gob movement and deformation in the front of landslide play a dragging role in the damage of the landslide. The boundaries and the sliding surface of the landslide have been determined by the ways of engineering geological mapping, drilling, geophysical investigation and deformation monitoring. The landslide is zoned based on the topography, material composition and deformation characters. The mitigation measures of ordered retaining structures in the landslide and anti-sliding pillar in the mine have been carried out according to the deformation characteristics, geological and environmental conditions and mining demand. Monitoring data show that the landslide keeps stable as the mitigation measure putting into effect.
2012, 20(5): 789-795.
Underground water-sealed oil storage is usually built in integral crystalline rock masses. Based on the theory of water sealing, oil is stored in underground cavern. In the surrounding rock, typical fluid-solid coupling characteristics exist in the process of construction and running. Based on flow-solid coupling theory of fractured rock mass, COMSOL Multiphysics software is used to simulate the fluid-structure interaction of surrounding rock under different working conditions. Research results show the follows. Without setting water curtains the underground water level at top of the cavern decreases obviously and forms the funnel, which could lead the spill of oil and gas. After the water curtains are set, the fall trend of water level is effectively controlled and the sealing of cavern is ensured. With setting water curtains, obvious stress concentration appears in straight wall, vault and the corner points of floor. But the plastic zone still does not appear in surrounding rock. The maximum displacement of cavern does not exceed 1mm. Besides, the stability of surrounding rock is good. The results can serve as references to the design and construction of underground engineering.
Underground water-sealed oil storage is usually built in integral crystalline rock masses. Based on the theory of water sealing, oil is stored in underground cavern. In the surrounding rock, typical fluid-solid coupling characteristics exist in the process of construction and running. Based on flow-solid coupling theory of fractured rock mass, COMSOL Multiphysics software is used to simulate the fluid-structure interaction of surrounding rock under different working conditions. Research results show the follows. Without setting water curtains the underground water level at top of the cavern decreases obviously and forms the funnel, which could lead the spill of oil and gas. After the water curtains are set, the fall trend of water level is effectively controlled and the sealing of cavern is ensured. With setting water curtains, obvious stress concentration appears in straight wall, vault and the corner points of floor. But the plastic zone still does not appear in surrounding rock. The maximum displacement of cavern does not exceed 1mm. Besides, the stability of surrounding rock is good. The results can serve as references to the design and construction of underground engineering.
2012, 20(5): 796-799.
Based on unsaturated soil recognition of loess disasters, this paper designs a vertical permeameter instrument on unsatu-rated soil. Experiment instrument consists of precipitation, runoff, seepage(sampling) and enrichment devices. It has important significance for studying on loess disasters and to simulate permeation process in loess under atmospheric precipitation and irrigation water. It can obtain parameters of seepage path, infiltration front velocity and water volume. The paper has established correlation between runoff volume and time(runoff velocity),displacement of infiltration front and time(seepage velocity),seepage volume and times(enrichment velocity).Experiments are conducted using unsaturated intact loess. The test results show that the experiment instrument is simple and useful, and can obtain permeation parameters of loess better.
Based on unsaturated soil recognition of loess disasters, this paper designs a vertical permeameter instrument on unsatu-rated soil. Experiment instrument consists of precipitation, runoff, seepage(sampling) and enrichment devices. It has important significance for studying on loess disasters and to simulate permeation process in loess under atmospheric precipitation and irrigation water. It can obtain parameters of seepage path, infiltration front velocity and water volume. The paper has established correlation between runoff volume and time(runoff velocity),displacement of infiltration front and time(seepage velocity),seepage volume and times(enrichment velocity).Experiments are conducted using unsaturated intact loess. The test results show that the experiment instrument is simple and useful, and can obtain permeation parameters of loess better.
2012, 20(5): 800-808.
Nowadays, the Wenner device of high-density electrical method has been used more and more widely in engineering. It is very significant to study its detecting depth of boulders in ground. This paper analyzes the factors influencing the detecting depth in detail. It studies the basic theory to the Wenner device in depth and then gets the relationship between the detecting depth and the four primary factors including agitation error, abnormal body radius, relative resistivity of abnormal body and electrode spacing. The research results show that, the detecting depth of Wenner device decreases with the increase of agitation error and increases nonlinearly with the increase of abnormal body radius. When the relative resistivity value is about one, the detecting depth is minimized. But when it increases to a certain value, the detecting depth does almost not change. When other factors are unchanged, the detecting depth increases with the increase of electrode spacing, which will reduce if the electrode spacing has exceedingly increased. Finally, by combining the theoretical analysis with field results, this paper proposes a method to improve the detecting depth of Wenner device to boulders based on the numerical simulation.
Nowadays, the Wenner device of high-density electrical method has been used more and more widely in engineering. It is very significant to study its detecting depth of boulders in ground. This paper analyzes the factors influencing the detecting depth in detail. It studies the basic theory to the Wenner device in depth and then gets the relationship between the detecting depth and the four primary factors including agitation error, abnormal body radius, relative resistivity of abnormal body and electrode spacing. The research results show that, the detecting depth of Wenner device decreases with the increase of agitation error and increases nonlinearly with the increase of abnormal body radius. When the relative resistivity value is about one, the detecting depth is minimized. But when it increases to a certain value, the detecting depth does almost not change. When other factors are unchanged, the detecting depth increases with the increase of electrode spacing, which will reduce if the electrode spacing has exceedingly increased. Finally, by combining the theoretical analysis with field results, this paper proposes a method to improve the detecting depth of Wenner device to boulders based on the numerical simulation.
2012, 20(5): 809-814.
This paper investigates a rock slope with height of 100m. It is an invalidated mine slope. The cliff side carving is going to be designed and constructed in this rock slope. But the complicated engineering geological structures will control the location and size of the cliff side carvings. Consequently, it is very important to investigate the development characteristics of faults, joints, kast caves, rock mass structures in this slope with valid methods. This paper studies the validity and some geological interpreting keys in applying the Electromagnetic Wave Tomography to investigating engineering geological conditions. As a result, the Electromagnetic Wave Tomography is able to investigate faults, karst caves and fissure zones, structure type of rock mass and zones in the slope. Furthermore, the change characteristics of rock electromagnetic absorption coefficient are valid to illustrate integrity zoning of slope rock mass. The result can provide the scientific evidence to the construction and design of complex geological slope.
This paper investigates a rock slope with height of 100m. It is an invalidated mine slope. The cliff side carving is going to be designed and constructed in this rock slope. But the complicated engineering geological structures will control the location and size of the cliff side carvings. Consequently, it is very important to investigate the development characteristics of faults, joints, kast caves, rock mass structures in this slope with valid methods. This paper studies the validity and some geological interpreting keys in applying the Electromagnetic Wave Tomography to investigating engineering geological conditions. As a result, the Electromagnetic Wave Tomography is able to investigate faults, karst caves and fissure zones, structure type of rock mass and zones in the slope. Furthermore, the change characteristics of rock electromagnetic absorption coefficient are valid to illustrate integrity zoning of slope rock mass. The result can provide the scientific evidence to the construction and design of complex geological slope.
2012, 20(5): 815-820.
The dissipating of excess pore pressure caused by pile sinking is one of the main factors result in time effect of ultimate bearing capacity of pile. This paper discusses the change rule of pile bearing capacity with time through the finite element simulation under the geological conditions of the pile foundation in the second phase project of the free port logistics processing zone in Dongjiang, Tianjin. It finds that the formula of pile bearing capacity about time effect in dredge fill can be used as reference for engineering use. It monitors the excess pore pressure at each observing point in order to verify the numerical simulation results. It discusses the change law of the distribution and dissipation of excess pore water pressure. Numerical simulation shows that the dissipation rate at the tip of pile can reach 97% 20d after pile sinking. The ultimate bearing capacity of pipe pile increases over time basically in accord with the dissipation of excess pore water pressure. It also introduces a formula of pile aging bearing capacity in dredge fill. Measured results show that the effective range of construction on dredger fill around the pile is 9-10 times the diameter of pile. The excess pore pressure increases with the depth increasing. The closer it from the pile, the greater the excess pore pressure is. The smaller the permeability coefficient of soil is,the more slowly the excess pore pressure dissipates.
The dissipating of excess pore pressure caused by pile sinking is one of the main factors result in time effect of ultimate bearing capacity of pile. This paper discusses the change rule of pile bearing capacity with time through the finite element simulation under the geological conditions of the pile foundation in the second phase project of the free port logistics processing zone in Dongjiang, Tianjin. It finds that the formula of pile bearing capacity about time effect in dredge fill can be used as reference for engineering use. It monitors the excess pore pressure at each observing point in order to verify the numerical simulation results. It discusses the change law of the distribution and dissipation of excess pore water pressure. Numerical simulation shows that the dissipation rate at the tip of pile can reach 97% 20d after pile sinking. The ultimate bearing capacity of pipe pile increases over time basically in accord with the dissipation of excess pore water pressure. It also introduces a formula of pile aging bearing capacity in dredge fill. Measured results show that the effective range of construction on dredger fill around the pile is 9-10 times the diameter of pile. The excess pore pressure increases with the depth increasing. The closer it from the pile, the greater the excess pore pressure is. The smaller the permeability coefficient of soil is,the more slowly the excess pore pressure dissipates.
2012, 20(5): 821-826.
Resistivity piezocone tests (RCPTU) is not only include the conventional piezocone tests, the continuous profile of electrical resistivity can also be obtained through this test. Therefore, the RCPTU has a wide application prospect in the environmental geotechnics. Electrical resistivity is a fundamental parameter to characterize the conductivity of soil, it is one of the inherent physical properties of soil. Each type of soil has an inherent resistivity, and its variation probably means that the soil is contaminated. Based on resistivity piezocone test results on a contaminated pesticide factory site, the influences of different pollutants on resistivity are analyzed in this paper. The identification of pollutants distribution and the contamination degree based on the resistivity index is also preliminary studied. Considering that the soil bulk resistivity can also be influenced by void ratio or relative density, and it is advised measured resistivity should be equivalent to a specified relative density which can be measured by RCPTU. Comparative analysis between the equivalent and inherent resistivity is conducted, and the deviation and rate of deviation are used to determine the pollutants distribution and degree of pollution. The results show that the change of resistivity can reflect the presence and degree of pollutions well.
Resistivity piezocone tests (RCPTU) is not only include the conventional piezocone tests, the continuous profile of electrical resistivity can also be obtained through this test. Therefore, the RCPTU has a wide application prospect in the environmental geotechnics. Electrical resistivity is a fundamental parameter to characterize the conductivity of soil, it is one of the inherent physical properties of soil. Each type of soil has an inherent resistivity, and its variation probably means that the soil is contaminated. Based on resistivity piezocone test results on a contaminated pesticide factory site, the influences of different pollutants on resistivity are analyzed in this paper. The identification of pollutants distribution and the contamination degree based on the resistivity index is also preliminary studied. Considering that the soil bulk resistivity can also be influenced by void ratio or relative density, and it is advised measured resistivity should be equivalent to a specified relative density which can be measured by RCPTU. Comparative analysis between the equivalent and inherent resistivity is conducted, and the deviation and rate of deviation are used to determine the pollutants distribution and degree of pollution. The results show that the change of resistivity can reflect the presence and degree of pollutions well.
2012, 20(5): 827-831.
In the Oujiang river estuary area, there is a big risk in the laying and being operated safely of submarine pipeline. The conventional method to test can't be used because of the strong tide and obvious shoal water. This paper uses sub-sea acoustic technology of side scan sonar to explore seafloor landform of the area where submarine pipelines go through effectively. Natural microrelief includes flat seafloor, large sand ridge, tidal creek, small pit, and alteration bulge. Anchor ditches are formed by dropping anchor and secondary microrelief developed naturaly later. They all are found and analysed. The result has an important significance to propose the corresponding solution countermeasures to different kinds of seafloor landforms and to reduce the topographic form influence on the stability of submarine pipeline.
In the Oujiang river estuary area, there is a big risk in the laying and being operated safely of submarine pipeline. The conventional method to test can't be used because of the strong tide and obvious shoal water. This paper uses sub-sea acoustic technology of side scan sonar to explore seafloor landform of the area where submarine pipelines go through effectively. Natural microrelief includes flat seafloor, large sand ridge, tidal creek, small pit, and alteration bulge. Anchor ditches are formed by dropping anchor and secondary microrelief developed naturaly later. They all are found and analysed. The result has an important significance to propose the corresponding solution countermeasures to different kinds of seafloor landforms and to reduce the topographic form influence on the stability of submarine pipeline.
2012, 20(5): 832-840.
The problem of underground water treatment in tunnel construction had plagued tunnel engineering community for a long time. The understanding of underground water action mechanism had not reached a consensus. So it needs to deep study on this issue from concept to methodology. This paper is based on the analysis of the research status. The impact analysis of tunnel construction on the changes in groundwater seepage is carried out. The physical model tests of the tunnel water pressure is done. Numerical analysis of tunnel lining water load and its associated problems are carried out. Then, the tunnel water load calculation model is proposed under different anti-drain modes, with tunnel groundwater treatment concepts and methods. The main innovation are as follows: a) the concept of high water pressure is clearly put forward, b)the conceptual model of the tunnel lining water pressure calculation, c)the tunnel waterproofing and drainage principles to adopt different processing strategies for different tunnel depth segments and groundwater development status. The research result provides a theoretical basis for design of high pressure water tunnel.
The problem of underground water treatment in tunnel construction had plagued tunnel engineering community for a long time. The understanding of underground water action mechanism had not reached a consensus. So it needs to deep study on this issue from concept to methodology. This paper is based on the analysis of the research status. The impact analysis of tunnel construction on the changes in groundwater seepage is carried out. The physical model tests of the tunnel water pressure is done. Numerical analysis of tunnel lining water load and its associated problems are carried out. Then, the tunnel water load calculation model is proposed under different anti-drain modes, with tunnel groundwater treatment concepts and methods. The main innovation are as follows: a) the concept of high water pressure is clearly put forward, b)the conceptual model of the tunnel lining water pressure calculation, c)the tunnel waterproofing and drainage principles to adopt different processing strategies for different tunnel depth segments and groundwater development status. The research result provides a theoretical basis for design of high pressure water tunnel.
2012, 20(5): 841-848.
The acoustic subbottom profiling technology is a geophysical method based on acoustical principle to continuously detect underwater stratigraphic structure and tectonics. Because of its high sensitivity, resolution, continuity and the ability of efficiently detecting the characteristics and distributions of underwater geological formations, it has been widely used in marine engineering prospect. An artificial island will be built in the Jinzhou Bay, Bohai Sea, where the sedimentary are gradually formed with the eustatism and transgression or retreat process since late Pleistocene. From top to bottom,the soilstrata are as follows: neritic facies silt or silty clay, littoral facies silt, continental facies clay, littoral facies silty clay, interbedded of marine and continental facies clay and silty clay. The typical acoustic subbottom profiles from Jinzhou Bay, Bohai Sea are analyzed and interpreted. Eight continuous strong acoustic reflection interfaces are recognized, and six acoustic sequences which have depositional environmental significance are confirmed. The thickness distribution of modern sedimentary and the depth distribution of bedrock are analyzed. According to the comparative study with the sedimentary stratigraphic and lithologic units of the engineering geological drillings, there is a good correspondence between the acoustic sequences confirmed by the subbottom profile and the geological strata of the drilling core. Therefore, the depositional environment is also deduced.
The acoustic subbottom profiling technology is a geophysical method based on acoustical principle to continuously detect underwater stratigraphic structure and tectonics. Because of its high sensitivity, resolution, continuity and the ability of efficiently detecting the characteristics and distributions of underwater geological formations, it has been widely used in marine engineering prospect. An artificial island will be built in the Jinzhou Bay, Bohai Sea, where the sedimentary are gradually formed with the eustatism and transgression or retreat process since late Pleistocene. From top to bottom,the soilstrata are as follows: neritic facies silt or silty clay, littoral facies silt, continental facies clay, littoral facies silty clay, interbedded of marine and continental facies clay and silty clay. The typical acoustic subbottom profiles from Jinzhou Bay, Bohai Sea are analyzed and interpreted. Eight continuous strong acoustic reflection interfaces are recognized, and six acoustic sequences which have depositional environmental significance are confirmed. The thickness distribution of modern sedimentary and the depth distribution of bedrock are analyzed. According to the comparative study with the sedimentary stratigraphic and lithologic units of the engineering geological drillings, there is a good correspondence between the acoustic sequences confirmed by the subbottom profile and the geological strata of the drilling core. Therefore, the depositional environment is also deduced.
2012, 20(5): 849-854.
There are many factors affecting anchoring effects of pre-stressed anchor cable. These factors are complicate and interactive. The anchoring force loss has a deep relation with properties of rock and soil. With theoretical analysis, experimental study and numerical simulation, this paper examines the influence mechanism of rock and soil creep formation and compression formation on anchoring force loss and anchoring force loss laws of pre-stressed anchor cable caused by solid rock, weak rock, broken rock and soil. The results show that the properties of rock and soil mass cause the difference of anchoring force loss rate. In addition, there is less loss rate if rock and soil mass is in good quality on the condition of the same initial anchoring force. This research result can be used to guide the design, construction and management of anchoring projects and improve economic and social benefits of the whole practice.
There are many factors affecting anchoring effects of pre-stressed anchor cable. These factors are complicate and interactive. The anchoring force loss has a deep relation with properties of rock and soil. With theoretical analysis, experimental study and numerical simulation, this paper examines the influence mechanism of rock and soil creep formation and compression formation on anchoring force loss and anchoring force loss laws of pre-stressed anchor cable caused by solid rock, weak rock, broken rock and soil. The results show that the properties of rock and soil mass cause the difference of anchoring force loss rate. In addition, there is less loss rate if rock and soil mass is in good quality on the condition of the same initial anchoring force. This research result can be used to guide the design, construction and management of anchoring projects and improve economic and social benefits of the whole practice.
2012, 20(5): 855-861.
The self-boring in-situ shear pressuremeter model test is simulated by particle flow theory and PFC3D(Particle Flow Code in three Dimensions) program. Based on indoor model test, a numerical model is formed in PFC3D.The loading procedure of SBISP test is simulated. A comparison between numerical and experimental results shows reasonable agreement. The displacement development mode and mesomechanics response of soil grains around the probe are studied under complex loading conditions. The numerical results show that the displacement of particles in central area increase with the shear stress imposed stepwise, and the direction of displacement vector is more significant too. The shape of displacement vector in influence area is a reverse cone under the fifth grade shear stress. The magnitude of shear stress depends on the friction coefficient of the probe, the shear stress-shear displacement curve is no longer changes when it reaches a certain value.
The self-boring in-situ shear pressuremeter model test is simulated by particle flow theory and PFC3D(Particle Flow Code in three Dimensions) program. Based on indoor model test, a numerical model is formed in PFC3D.The loading procedure of SBISP test is simulated. A comparison between numerical and experimental results shows reasonable agreement. The displacement development mode and mesomechanics response of soil grains around the probe are studied under complex loading conditions. The numerical results show that the displacement of particles in central area increase with the shear stress imposed stepwise, and the direction of displacement vector is more significant too. The shape of displacement vector in influence area is a reverse cone under the fifth grade shear stress. The magnitude of shear stress depends on the friction coefficient of the probe, the shear stress-shear displacement curve is no longer changes when it reaches a certain value.
2012, 20(5): 862-867.
The GFRP anchors have advantages over the steel anchors in terms of better corrosion resistance, higher strength-to-weight ratio and so forth, in recent years, they have been gradually utilized to stabilize slopes and other geo-structures. However, stability condition of these geo-structures may be significantly affected by the time-dependent mechanical characteristics of GFRP anchors. According to the pullout mechanism of GFRP anchors, a visco-elastic model which is based on the Merchant rheological model, is proposed to describe the time dependent pullout behavior of GFRP anchors. The finite difference method is used to solve the third-order partial governing equation derived from the proposed model. The distributions of tensile force, shear stress, and displacement and their variations with time are calculated. Furthermore, a parametric study is conducted to study the influence of model parameters on the time-dependent pullout behavior of GFRP anchors. Conclusions relevant to the reinforcement mechanism of GFRP anchor are drawn subsequently.
The GFRP anchors have advantages over the steel anchors in terms of better corrosion resistance, higher strength-to-weight ratio and so forth, in recent years, they have been gradually utilized to stabilize slopes and other geo-structures. However, stability condition of these geo-structures may be significantly affected by the time-dependent mechanical characteristics of GFRP anchors. According to the pullout mechanism of GFRP anchors, a visco-elastic model which is based on the Merchant rheological model, is proposed to describe the time dependent pullout behavior of GFRP anchors. The finite difference method is used to solve the third-order partial governing equation derived from the proposed model. The distributions of tensile force, shear stress, and displacement and their variations with time are calculated. Furthermore, a parametric study is conducted to study the influence of model parameters on the time-dependent pullout behavior of GFRP anchors. Conclusions relevant to the reinforcement mechanism of GFRP anchor are drawn subsequently.
2012, 20(5): 868-876.
This paper aims to study the seawater intrusion problems in the sandy aquifer, and determine the development and evolution of saltwater-wedge in the aqueous medium through the seawater intrusion process. It simulates seawater intrusion process in the soil bin, using the high-density resistivity probe observing system to remote and real-time monitor the vertical resistivity changes of the soil through the seawater intrusion process. It determines the development of the seawater intrusion by analyzing the resistivity data. The result shows that the high-density resistivity probe is good at monitoring the occurrence and development of seawater intrusion. The formation of the salt-fresh mutation interface, the evolution of the transition zone and the change of salt-fresh water interface are monitored. The high-density resistivity probe is sensitive to the change of seawater interface. It is useful to real-time monitor and pre-warning the seawater intrusion.
This paper aims to study the seawater intrusion problems in the sandy aquifer, and determine the development and evolution of saltwater-wedge in the aqueous medium through the seawater intrusion process. It simulates seawater intrusion process in the soil bin, using the high-density resistivity probe observing system to remote and real-time monitor the vertical resistivity changes of the soil through the seawater intrusion process. It determines the development of the seawater intrusion by analyzing the resistivity data. The result shows that the high-density resistivity probe is good at monitoring the occurrence and development of seawater intrusion. The formation of the salt-fresh mutation interface, the evolution of the transition zone and the change of salt-fresh water interface are monitored. The high-density resistivity probe is sensitive to the change of seawater interface. It is useful to real-time monitor and pre-warning the seawater intrusion.
2012, 20(5): 877-887.
This paper is based on the karst area of geotechnical engineering. It uses the difference in physical characteristic of the rack and soil and the wave impedance and resistivity differences. It comparatively analyses the high density resistivity method, the transient electromagnetic method, the geological radar method and other geophysical prospecting methods. Finally it determines the high-density electrical method, the seismic imaging method, the acoustic logging and drilling CT methods, as well as the surface and subsurface geophysical exploration methods to detect the site conditions of combining the karst distribution and the development conditions.
This paper is based on the karst area of geotechnical engineering. It uses the difference in physical characteristic of the rack and soil and the wave impedance and resistivity differences. It comparatively analyses the high density resistivity method, the transient electromagnetic method, the geological radar method and other geophysical prospecting methods. Finally it determines the high-density electrical method, the seismic imaging method, the acoustic logging and drilling CT methods, as well as the surface and subsurface geophysical exploration methods to detect the site conditions of combining the karst distribution and the development conditions.
2012, 20(5): 889-898.
The NSFC proposals and grants of engineering geology in 2012 were analyzed. The amount of proposals increases fast. The competitiveness of the proposals has been improved. The age distribution of the applicant tends to be reasonable. There are differences of funded ratio between different age group. the talent team construction has obtained initial effect in engineering geology.
The NSFC proposals and grants of engineering geology in 2012 were analyzed. The amount of proposals increases fast. The competitiveness of the proposals has been improved. The age distribution of the applicant tends to be reasonable. There are differences of funded ratio between different age group. the talent team construction has obtained initial effect in engineering geology.
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