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Editor Work2012 Vol. 20, No. 3
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2012, 20(3): 305-310.
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According to statistics, the damage caused by earthquake-induced landslides and collapses can account for about 40% of all that causes by earthquake. As for the mechanisms and modes of slope deformation and failure under seismic force,a lot of previous theories and achievements have been reached. But, numerical simulation research is limited. The seismic intensity of the northern mountainous area of Shifang City, Sichuan province reached 11 degrees during the 5.12 Wenchuan earthquake. The remote sensing system had interpreted up to 161 sites of geological hazards induced by that. Their basic failure modes are bedding-layer cutting slides and slipping collapses. This paper considered two typical geo-hazards triggered by the 5.12 Wenchuan earthquake, and analyzed their stereographic projection. it worked out the combination modes of preferred structure planes which controlled the slope stability. Then it applied numerical simulation with discrete elements software to simulate their process of failure. The results show the following two failure modes. The first mode of slope failure during earthquake is that, the layered slopes that dip gently outwards crack its top at first, meanwhile the structure planes inside the slope start to undergo shear deformation. As the cracks on the top extend downwards and when these cracks reach the structure planes dip outwards inside the slope, the entire slope will slide along those connected planes. Their deformation and failure mechanism is slide-rip. Their mode of failure is bedding-layer cutting slide. The second mode of slope failure during earthquake is as follows. The steep block slopes crack their tops and loose themselves at first. Then the blocks cut and formed by structure planes start to undergo shear deformation along the structure planes which dip gently inwards or horizontal at the bottom of those tensile cracks. Then these blocks gradually slip outwards due to the durative earthquake, roll and fall down the slopes. Their deformation and failure mechanism is rip-slip. Their mode of failure is slipping collapse.
According to statistics, the damage caused by earthquake-induced landslides and collapses can account for about 40% of all that causes by earthquake. As for the mechanisms and modes of slope deformation and failure under seismic force,a lot of previous theories and achievements have been reached. But, numerical simulation research is limited. The seismic intensity of the northern mountainous area of Shifang City, Sichuan province reached 11 degrees during the 5.12 Wenchuan earthquake. The remote sensing system had interpreted up to 161 sites of geological hazards induced by that. Their basic failure modes are bedding-layer cutting slides and slipping collapses. This paper considered two typical geo-hazards triggered by the 5.12 Wenchuan earthquake, and analyzed their stereographic projection. it worked out the combination modes of preferred structure planes which controlled the slope stability. Then it applied numerical simulation with discrete elements software to simulate their process of failure. The results show the following two failure modes. The first mode of slope failure during earthquake is that, the layered slopes that dip gently outwards crack its top at first, meanwhile the structure planes inside the slope start to undergo shear deformation. As the cracks on the top extend downwards and when these cracks reach the structure planes dip outwards inside the slope, the entire slope will slide along those connected planes. Their deformation and failure mechanism is slide-rip. Their mode of failure is bedding-layer cutting slide. The second mode of slope failure during earthquake is as follows. The steep block slopes crack their tops and loose themselves at first. Then the blocks cut and formed by structure planes start to undergo shear deformation along the structure planes which dip gently inwards or horizontal at the bottom of those tensile cracks. Then these blocks gradually slip outwards due to the durative earthquake, roll and fall down the slopes. Their deformation and failure mechanism is rip-slip. Their mode of failure is slipping collapse.
2012, 20(3): 311-317.
This paper assumes the following four conditions. The movement of the landslide mass meets the requirements of Newton fluid dynamics equation. There is only lateral pressure inside the moving mass. The volume of the mass does not change. And all energy loss during motion is caused by friction in the motive model proposed by Sassa Kyoji. It derives the two dimensional movement formulas on the basis of the four assumptions. Meanwhile, the simulation program is compiled for the formulas. A case study is carried out. It is about Yanlian Yuanyoushan loess slow transitional landslide in Yanan City, Shaanxi Province. The geological model is set up by recoverying the topography before sliding and seeking out the slip surface by in-suit drilling. In the two-dimensional motive simulation, different residual friction angles are adopted as the sliding frictional angle. The results show that the run-out distance and the accumulation form are both very close to the in-situ measured results. Finally, the possible run-out distance of the critical slope on the left side of Yanlian yuanyoushan landslide is predicted with this movement model. And the potential hazards are also assessed. The result presented in this paper can provide a simple and applicable method of prediction for the sliding distance of landslides.
This paper assumes the following four conditions. The movement of the landslide mass meets the requirements of Newton fluid dynamics equation. There is only lateral pressure inside the moving mass. The volume of the mass does not change. And all energy loss during motion is caused by friction in the motive model proposed by Sassa Kyoji. It derives the two dimensional movement formulas on the basis of the four assumptions. Meanwhile, the simulation program is compiled for the formulas. A case study is carried out. It is about Yanlian Yuanyoushan loess slow transitional landslide in Yanan City, Shaanxi Province. The geological model is set up by recoverying the topography before sliding and seeking out the slip surface by in-suit drilling. In the two-dimensional motive simulation, different residual friction angles are adopted as the sliding frictional angle. The results show that the run-out distance and the accumulation form are both very close to the in-situ measured results. Finally, the possible run-out distance of the critical slope on the left side of Yanlian yuanyoushan landslide is predicted with this movement model. And the potential hazards are also assessed. The result presented in this paper can provide a simple and applicable method of prediction for the sliding distance of landslides.
2012, 20(3): 318-325.
The Zoumaling stream is a typical debris flow gully because of the large numbers of loose geomaterials induced by the Wenchuan Earthquake. Three debris flow events have occurred after the Earthquake, and caused serious property loss. Two typical debris flow events occurred respectively on September 24, 2008 and on August 13, 2010.This paper combines the RS image and field investigation data. It analyzes the formation conditions of the Zoumaling debris flows, and compares the evolution characters of the gully after three rainy seasons after Wenchuan earthquake using RS image data of 2008, 2009 and 2010.The results show that the source initiation of the Zoumaling debris flows with a complex supply process in different rainfall intensity. The debris flow initiation began from the branch gullies, and then evolved into a whole basin debris flow. Secondly, after the three rainy seasons of 2008、2009 and 2010,the source volume and its initiation process is changed. The volume of collapses has increased 1.87%.Landslide has increased 25.35%.Sediment of channels and slopes has reduced 67.47%.Most of these have transformed into debris flow sediments. Thirdly, at different rainfall intensity conditions, the boundary of the Zoumaling deposition area has changed obviously. There is an overlay relation among the deposition fans formed in different rainy seasons. Comparing the deposit extent of the Zoumaling -9.24 and the front edge of the Zoumaling -8.13 deposition fan and using the RS images interpretation, the deposition area of the Zoumaling -8.13 is 8.76×104m2. Finally, this paper analyzes the formation and evolution trend of this debris flow gully. The results show that the Zoumaling is a high frequency debris flow gully. The large amount of loose geomaterials are still distributed in the gully, which is the advantageous factor for large debris flow to occur.
The Zoumaling stream is a typical debris flow gully because of the large numbers of loose geomaterials induced by the Wenchuan Earthquake. Three debris flow events have occurred after the Earthquake, and caused serious property loss. Two typical debris flow events occurred respectively on September 24, 2008 and on August 13, 2010.This paper combines the RS image and field investigation data. It analyzes the formation conditions of the Zoumaling debris flows, and compares the evolution characters of the gully after three rainy seasons after Wenchuan earthquake using RS image data of 2008, 2009 and 2010.The results show that the source initiation of the Zoumaling debris flows with a complex supply process in different rainfall intensity. The debris flow initiation began from the branch gullies, and then evolved into a whole basin debris flow. Secondly, after the three rainy seasons of 2008、2009 and 2010,the source volume and its initiation process is changed. The volume of collapses has increased 1.87%.Landslide has increased 25.35%.Sediment of channels and slopes has reduced 67.47%.Most of these have transformed into debris flow sediments. Thirdly, at different rainfall intensity conditions, the boundary of the Zoumaling deposition area has changed obviously. There is an overlay relation among the deposition fans formed in different rainy seasons. Comparing the deposit extent of the Zoumaling -9.24 and the front edge of the Zoumaling -8.13 deposition fan and using the RS images interpretation, the deposition area of the Zoumaling -8.13 is 8.76×104m2. Finally, this paper analyzes the formation and evolution trend of this debris flow gully. The results show that the Zoumaling is a high frequency debris flow gully. The large amount of loose geomaterials are still distributed in the gully, which is the advantageous factor for large debris flow to occur.
2012, 20(3): 326-333.
At 07: 49(Beijing time)on April 14, 2010,a catastrophic earthquake with Ms 7.1 struck Yushu County,Qinghai Province,China.2036 landslides were interpreted from aerial photographs and remote sensing images,verified by selected field checking.The spatial distribution of the landslides was evidently strongly controlled by the locations of the main surface fault ruptures.The landslides commonly occurred close together.Most of the landslides were small.The landslides were of various types.They were mainly shallow,disrupted landslides,but also included rock falls,deep-seated landslides,liquefied landslides, and compound landslides.The aim of this study was to apply and validate logistic regression model for the Yushu earthquake triggered landslide hazard mapping.The Geographic Information Systems(GIS) and Remote Sensing(RS)technologies were used.A spatial database was developed and analyzed using GIS technology.It includes the landslides and associated controlling parameters which may have influence on the occurrence of landslides..The twelve factors that influence landslide occurrence were created in raster data format base on GIS platform.They include elevation,slope angle,slope aspect,slope curvature,slope position,drainages,lithology,faults,roads,normalized difference vegetation index(NDVI),co-seismic main surface fault-ruptures, and peak ground acceleration(PGA).the coefficients of the evaluation variables were estimated using logistic regression model and were used to calculate the landslide hazard index for the entire study area within a GIS environment.The validation result showed a success rate of 83.21% between the hazard map and the locations of Yushu earthquake triggered landslides.The landslide hazard assessment rank result showed that the"very high hazard"level covers about 4.97% of the total study area but has a number of 766 landslides(37.62% of the total landslides number),which representing good quality of the landslide hazard map.The sequence of the landslide number density percentage descends expeditiously accompany with the hazard level decreasing.
At 07: 49(Beijing time)on April 14, 2010,a catastrophic earthquake with Ms 7.1 struck Yushu County,Qinghai Province,China.2036 landslides were interpreted from aerial photographs and remote sensing images,verified by selected field checking.The spatial distribution of the landslides was evidently strongly controlled by the locations of the main surface fault ruptures.The landslides commonly occurred close together.Most of the landslides were small.The landslides were of various types.They were mainly shallow,disrupted landslides,but also included rock falls,deep-seated landslides,liquefied landslides, and compound landslides.The aim of this study was to apply and validate logistic regression model for the Yushu earthquake triggered landslide hazard mapping.The Geographic Information Systems(GIS) and Remote Sensing(RS)technologies were used.A spatial database was developed and analyzed using GIS technology.It includes the landslides and associated controlling parameters which may have influence on the occurrence of landslides..The twelve factors that influence landslide occurrence were created in raster data format base on GIS platform.They include elevation,slope angle,slope aspect,slope curvature,slope position,drainages,lithology,faults,roads,normalized difference vegetation index(NDVI),co-seismic main surface fault-ruptures, and peak ground acceleration(PGA).the coefficients of the evaluation variables were estimated using logistic regression model and were used to calculate the landslide hazard index for the entire study area within a GIS environment.The validation result showed a success rate of 83.21% between the hazard map and the locations of Yushu earthquake triggered landslides.The landslide hazard assessment rank result showed that the"very high hazard"level covers about 4.97% of the total study area but has a number of 766 landslides(37.62% of the total landslides number),which representing good quality of the landslide hazard map.The sequence of the landslide number density percentage descends expeditiously accompany with the hazard level decreasing.
2012, 20(3): 334-339.
The rockslide-debris avalanche is a geological disaster of great danger and always causes disastrous catastrophes because of its high velocity and unexpected long runout. Scholars in China had made a lot of forward-looking results for the high-speed rockslide-debris flows after Wenchuan Earthquake. A majority of the research results on this field have not been widely accepted due to itself complication. This paper takes the Donghekou rockslide-debris avalanche in Qingchuan County triggered by Wenchuan Earthquake as example to reveal the moving mechanism of rockslide-debris avalanches. The dynamic analysis software of DAN-W is applied to the creation of three different rheological models. They are Friction model, Voellmy model and F-V model to simulate on the motion behavior of flow slides and put an emphasis on the travel distance, speed characteristics at different intervals, distribution of the deposits. The volume and duration are estimated. The results reveal that applying different rheological models to different moving stages have reasonable results. The Friction model is better to simulate the landslide at set-out phase and short-runout phase. The Voellmy model has advantages of simulating flow debris at long run-out phase. The two-rheological model"F-V"provides the best simulation of the Donghekou rockslide-debris avalanche movement. The best fitting rheological parameters friction angle φ=18°,friction coefficient μ=0.1 and turbulence parameter ξ=400m·s-2 have been found by the back analysis.
The rockslide-debris avalanche is a geological disaster of great danger and always causes disastrous catastrophes because of its high velocity and unexpected long runout. Scholars in China had made a lot of forward-looking results for the high-speed rockslide-debris flows after Wenchuan Earthquake. A majority of the research results on this field have not been widely accepted due to itself complication. This paper takes the Donghekou rockslide-debris avalanche in Qingchuan County triggered by Wenchuan Earthquake as example to reveal the moving mechanism of rockslide-debris avalanches. The dynamic analysis software of DAN-W is applied to the creation of three different rheological models. They are Friction model, Voellmy model and F-V model to simulate on the motion behavior of flow slides and put an emphasis on the travel distance, speed characteristics at different intervals, distribution of the deposits. The volume and duration are estimated. The results reveal that applying different rheological models to different moving stages have reasonable results. The Friction model is better to simulate the landslide at set-out phase and short-runout phase. The Voellmy model has advantages of simulating flow debris at long run-out phase. The two-rheological model"F-V"provides the best simulation of the Donghekou rockslide-debris avalanche movement. The best fitting rheological parameters friction angle φ=18°,friction coefficient μ=0.1 and turbulence parameter ξ=400m·s-2 have been found by the back analysis.
2012, 20(3): 340-349.
Under the influence of 5.12 earthquake, the geo-hazards are extreme serious in the reach of the Yuzi Stream form Gengda to Yingxiu. The geo-hazard chains are also very prominent. Through field investigation and remote sensing interpretation, this paper tries to reveal the characteristics and genetic process and conditions of geologic hazards in the stream. Based on their characteristics, the geo-hazards are divided into three types. They are (1) instability and crash of the highly weathered rock-mass and soil on the upper slopes, (2) collapse of massive rock-mass slope, and (3) local downpour types of debris flows. The geo-hazards are controlled by seismic fault and the density is higher on the north shore. They show significant deviations between the two sides of Maowen fault zone. 51 collapses and 17 debris flows are analyzed. The geo-hazards mainly took place on the slopes steeper than 40°. The instability positions are mainly upon the parts with slope gradients more than 0.4 and failure zones distribute on the upside of the slopes. Debris flows mainly occur in the valley of the large slope and manhood. The geo-hazards can be transformed into small-scale single collapses and debris flows induced by rainfall. There are mainly two types of geo-hazard chains: (1) geo-hazard chains due to inner dynamic-"earthquake → collapses → stream squeezed, road destroyed and the barrier lakes". The genetic process includes three stages: high-speed start, glide motion, stoppage; (2) geo-hazards chains due to the inner and outer dynamic coupling effect-"earthquake → collapses and shattered mountains → rainstorm →debris flows → stream squeezed, road destroyed and the barrier lakes". The genetic process can be divided into four parts: preparation, dam-breaking after the valley blocked, bed-making and stoppage. The genetic conditions of geo-hazard chains can be concluded as follows: vulnerable geology environment, high steep slope (>50m, >40°) collapsed and shattered by the strong ground motion, the heavy rainfall and suitable conditions for blocking the river.
Under the influence of 5.12 earthquake, the geo-hazards are extreme serious in the reach of the Yuzi Stream form Gengda to Yingxiu. The geo-hazard chains are also very prominent. Through field investigation and remote sensing interpretation, this paper tries to reveal the characteristics and genetic process and conditions of geologic hazards in the stream. Based on their characteristics, the geo-hazards are divided into three types. They are (1) instability and crash of the highly weathered rock-mass and soil on the upper slopes, (2) collapse of massive rock-mass slope, and (3) local downpour types of debris flows. The geo-hazards are controlled by seismic fault and the density is higher on the north shore. They show significant deviations between the two sides of Maowen fault zone. 51 collapses and 17 debris flows are analyzed. The geo-hazards mainly took place on the slopes steeper than 40°. The instability positions are mainly upon the parts with slope gradients more than 0.4 and failure zones distribute on the upside of the slopes. Debris flows mainly occur in the valley of the large slope and manhood. The geo-hazards can be transformed into small-scale single collapses and debris flows induced by rainfall. There are mainly two types of geo-hazard chains: (1) geo-hazard chains due to inner dynamic-"earthquake → collapses → stream squeezed, road destroyed and the barrier lakes". The genetic process includes three stages: high-speed start, glide motion, stoppage; (2) geo-hazards chains due to the inner and outer dynamic coupling effect-"earthquake → collapses and shattered mountains → rainstorm →debris flows → stream squeezed, road destroyed and the barrier lakes". The genetic process can be divided into four parts: preparation, dam-breaking after the valley blocked, bed-making and stoppage. The genetic conditions of geo-hazard chains can be concluded as follows: vulnerable geology environment, high steep slope (>50m, >40°) collapsed and shattered by the strong ground motion, the heavy rainfall and suitable conditions for blocking the river.
2012, 20(3): 350-354.
Prediction of landslide-generated waves involves the dynamic landslide, geotechnical mechanics, fluid mechanics and other disciplinary fields. Also, landslide induced surge is a complicated fluid-solid coupling problem. Especially with the development of large-scale hydropower project construction, the surge induced by landslide is an important factor for evaluating effects of landslide hazards on the reservoir area. The Coupled Euler and Lagrange algorithm (CEL) has a strong advantage in solving complex fluid-solid interaction problems. Based on the results of a laboratory model test which have been done by other people, and by using CEL algorithm, this paper simulates this whole process. The analysis results indicate that the results obtained by CEL simulation is agree well with the laboratory test, which verifies the feasibility and reliability of CEL algorithm on solve the problems of landslide surge.
Prediction of landslide-generated waves involves the dynamic landslide, geotechnical mechanics, fluid mechanics and other disciplinary fields. Also, landslide induced surge is a complicated fluid-solid coupling problem. Especially with the development of large-scale hydropower project construction, the surge induced by landslide is an important factor for evaluating effects of landslide hazards on the reservoir area. The Coupled Euler and Lagrange algorithm (CEL) has a strong advantage in solving complex fluid-solid interaction problems. Based on the results of a laboratory model test which have been done by other people, and by using CEL algorithm, this paper simulates this whole process. The analysis results indicate that the results obtained by CEL simulation is agree well with the laboratory test, which verifies the feasibility and reliability of CEL algorithm on solve the problems of landslide surge.
2012, 20(3): 355-361.
The behavior of micropiles under the effect of landslide is summarized by micropiles and landslide model tests. A new design method of micropiles for landslide reinforcement is proposed based on the test results. The test results show that the damage of micropiles is caused by the poor bending and shearing resistance. The skid-resisting capacity transforms from bending and shearing resistance to pulling resistance of the steel when micropiles damage. The horizontal displacement of every micropile in groups is similar. The landslide thrust effecting on the micropiles reduces along the sliding direction. A design method of micropiles is proposed based on the results. The skid-resisting capacity is provided by the shearing resistance of micropiles near the plane of sliding. The uneven distribution of landslide thrust is considered in the method.
The behavior of micropiles under the effect of landslide is summarized by micropiles and landslide model tests. A new design method of micropiles for landslide reinforcement is proposed based on the test results. The test results show that the damage of micropiles is caused by the poor bending and shearing resistance. The skid-resisting capacity transforms from bending and shearing resistance to pulling resistance of the steel when micropiles damage. The horizontal displacement of every micropile in groups is similar. The landslide thrust effecting on the micropiles reduces along the sliding direction. A design method of micropiles is proposed based on the results. The skid-resisting capacity is provided by the shearing resistance of micropiles near the plane of sliding. The uneven distribution of landslide thrust is considered in the method.
2012, 20(3): 362-368.
Longwangping landslide can be divided into the upper landslide and the lower landslide. Based on the engineering geological condition investigation, the deformation process is analyzed. The deformation and failure mode are determined. The upper landslide belongs to the pushing mode and the lower landslide is the pulling mode. With the unbalanced thrust transfer coefficient method, the landslide stability is evaluated both in normal natural state and the heavy rain conditions. Using the finite element method, the change regularity of the seepage field and stress field considering heavy rain is obtained. Then the influence by storm on the landslide stability is estimated. The result shows that under the normal natural condition, the landslide is stable. But under the heavy rainfall, Long-wangping landslide is in the less stable state.
Longwangping landslide can be divided into the upper landslide and the lower landslide. Based on the engineering geological condition investigation, the deformation process is analyzed. The deformation and failure mode are determined. The upper landslide belongs to the pushing mode and the lower landslide is the pulling mode. With the unbalanced thrust transfer coefficient method, the landslide stability is evaluated both in normal natural state and the heavy rain conditions. Using the finite element method, the change regularity of the seepage field and stress field considering heavy rain is obtained. Then the influence by storm on the landslide stability is estimated. The result shows that under the normal natural condition, the landslide is stable. But under the heavy rainfall, Long-wangping landslide is in the less stable state.
2012, 20(3): 369-377.
Landslides in existing soil and rock debris slopes have become one of the major hazards in projects. The physical, hydraulic and mechanical properties of debris landslide are summarized systematically in this paper. They are the physical, mechanical and permeability properties of sliding-body, the particle composition, chemical components, microstructure, physical properties, mechanical properties and weakening properties of sliding-zone soil. The analyses are based on the engineering geological conditions of debris landslide and extensive literature review and engineering practice, According to the engineering geological characteristics of debris landslide, both engineering geological and hydro-geological models were deduced. They provide a reference for the determination boundary conditions of groundwater seepage induced by rainfall, water level fluctuation of reservoir and rivers in sliding-body. Finally, various prevention measures of debris landslide are systematically summarized.
Landslides in existing soil and rock debris slopes have become one of the major hazards in projects. The physical, hydraulic and mechanical properties of debris landslide are summarized systematically in this paper. They are the physical, mechanical and permeability properties of sliding-body, the particle composition, chemical components, microstructure, physical properties, mechanical properties and weakening properties of sliding-zone soil. The analyses are based on the engineering geological conditions of debris landslide and extensive literature review and engineering practice, According to the engineering geological characteristics of debris landslide, both engineering geological and hydro-geological models were deduced. They provide a reference for the determination boundary conditions of groundwater seepage induced by rainfall, water level fluctuation of reservoir and rivers in sliding-body. Finally, various prevention measures of debris landslide are systematically summarized.
2012, 20(3): 378-386.
The common slopes classification systems are suitable for a road, railway or a certain area landslide risk assessment, which aims to ordering the priority of the landslide count-measurements. The study of using slope classifying system to assess the landslide risk is rare in open literature. The environmental conditions of loess collapse are similar, whereas the controlling factors to the collapse have differences at individual slopes. So the scoring and grading are a good way to assess the risk of the loess collapse. This paper selects a loess ravine area of 3.2 km2 in suburban district of Yanan, Shannxi, China as study area. It is implemented on the basis of analysis to the assessing factors and their weights, which have been done in previous works. It uses the hydrology methods to zone the assessing units, sets four grading standard for the hazards factors and five grading standard for the consequence factors, and synthesizes the hazards results and the consequence results to set the risk judge matrix. Accordingly, it designs the slope classifying system for the loess collapse risk assessment. Applying this classification system at 37 loess slope units, the result shows that the collapse risk level of each unit has not a regular distribution. It only depends on the local geological conditions and the elements in the risk. The statistics of units risk shows phenomena of "much in middle and less in both ends", which means the area of "high risk" and "very low risk" is very less (only 27%), whereas the area of "moderate risk" and "low risk" is much more (73%). This classifying system can be used as a semi-quantitative method to assess the collapse risk at the loess slopes.
The common slopes classification systems are suitable for a road, railway or a certain area landslide risk assessment, which aims to ordering the priority of the landslide count-measurements. The study of using slope classifying system to assess the landslide risk is rare in open literature. The environmental conditions of loess collapse are similar, whereas the controlling factors to the collapse have differences at individual slopes. So the scoring and grading are a good way to assess the risk of the loess collapse. This paper selects a loess ravine area of 3.2 km2 in suburban district of Yanan, Shannxi, China as study area. It is implemented on the basis of analysis to the assessing factors and their weights, which have been done in previous works. It uses the hydrology methods to zone the assessing units, sets four grading standard for the hazards factors and five grading standard for the consequence factors, and synthesizes the hazards results and the consequence results to set the risk judge matrix. Accordingly, it designs the slope classifying system for the loess collapse risk assessment. Applying this classification system at 37 loess slope units, the result shows that the collapse risk level of each unit has not a regular distribution. It only depends on the local geological conditions and the elements in the risk. The statistics of units risk shows phenomena of "much in middle and less in both ends", which means the area of "high risk" and "very low risk" is very less (only 27%), whereas the area of "moderate risk" and "low risk" is much more (73%). This classifying system can be used as a semi-quantitative method to assess the collapse risk at the loess slopes.
2012, 20(3): 387-391.
The mechanical characteristics of natural soils are significantly affected by their structure and original stress. As undisturbed soil and remolded soil possess different structural features, they demonstrate different mechanical properties in the case of minor stress. At present, lots of structural models have been established by remolded soil and experimental conditions without considering structure and original stress. Under the classical theories of elasto-plastic, based on soft clay in Guilin areas, combine with test indoor, according to the former model, an elasto-plastic constitutive model has been established to synchronously consider the structural characters and the original stress state based on the Modified Cam Clay. The comparison and analysis of various calculated results have shown the rationality and validity of the model. The applications of the model expressions make the strain result more correspond to the engineering practice. They have important significance for controlling not only rate of loading but also size of load grade during highway filled soil in Guilin areas.
The mechanical characteristics of natural soils are significantly affected by their structure and original stress. As undisturbed soil and remolded soil possess different structural features, they demonstrate different mechanical properties in the case of minor stress. At present, lots of structural models have been established by remolded soil and experimental conditions without considering structure and original stress. Under the classical theories of elasto-plastic, based on soft clay in Guilin areas, combine with test indoor, according to the former model, an elasto-plastic constitutive model has been established to synchronously consider the structural characters and the original stress state based on the Modified Cam Clay. The comparison and analysis of various calculated results have shown the rationality and validity of the model. The applications of the model expressions make the strain result more correspond to the engineering practice. They have important significance for controlling not only rate of loading but also size of load grade during highway filled soil in Guilin areas.
2012, 20(3): 392-396.
Shanghai had suffered severe ground subsidence, mainly due to the shallow soil consolidation caused by shallow aquifer exploitation. Thereafter, pumping aquifer is adjusted from the shallow aquifers to deep ones. The land subsidence was effectively controlled. However, in the early 21 century, through water level and borehole extensometer monitoring, it found that deep aquifer will become the major compaction layer with the increasing exploitation. The deformation of the deep aquifer shows a significant nonlinear compaction characteristic. Even if the water level is generally uplift, the compaction continues. It is very necessary to research the consolidation mechanism model for the ground subsidence prevention and control. The traditional Terzaghi theory regards sand skeleton as instantaneous materials, ignoring the rheological nature. So there is no way to explain the above-mentioned phenomenon. Based on the studies of scholars at home and abroad, taking into account the differences in rheological properties before and after the pre-consolidation pressure, the viscoelastic-plastic consolidation model for deep aquifer is established. The deep fourth aquifer long-term compaction deformation is simulated based on the test parameters, combined with the Tangqiao F16 borehole extensometer monitoring results. The simulation result shows that the model used well reflects the aquifer long-term nonlinear compaction behavior. The study result is helpful to guide the prevention and control of ground settlement.
Shanghai had suffered severe ground subsidence, mainly due to the shallow soil consolidation caused by shallow aquifer exploitation. Thereafter, pumping aquifer is adjusted from the shallow aquifers to deep ones. The land subsidence was effectively controlled. However, in the early 21 century, through water level and borehole extensometer monitoring, it found that deep aquifer will become the major compaction layer with the increasing exploitation. The deformation of the deep aquifer shows a significant nonlinear compaction characteristic. Even if the water level is generally uplift, the compaction continues. It is very necessary to research the consolidation mechanism model for the ground subsidence prevention and control. The traditional Terzaghi theory regards sand skeleton as instantaneous materials, ignoring the rheological nature. So there is no way to explain the above-mentioned phenomenon. Based on the studies of scholars at home and abroad, taking into account the differences in rheological properties before and after the pre-consolidation pressure, the viscoelastic-plastic consolidation model for deep aquifer is established. The deep fourth aquifer long-term compaction deformation is simulated based on the test parameters, combined with the Tangqiao F16 borehole extensometer monitoring results. The simulation result shows that the model used well reflects the aquifer long-term nonlinear compaction behavior. The study result is helpful to guide the prevention and control of ground settlement.
2012, 20(3): 397-402.
Desiccation cracks of compacted clay liner might have a great effect on its hydraulic conductivity. During the decrease of its water content, its crack area ratio, length and width will increase. Desiccation cracks can be divided into the major and the minor types. There are obvious differences for the change rate of crack parameters before and after minor cracks appear. Wider cracks can't entirely heal after hydration, which reveals that the wet-dry cycling is irreversible for the compacted clay liner. Development of cracks in the clay can be monitored successfully with the Araldite that was put on the inside wall surface of the test cylinder. The Araldite can also prevent side-leakage. One wet-dry cycling can increase the hydraulic conductivity of the compacted clay liner for nearly two orders in its magnitude. Non-completely-healing cracks and microcracks might be the main reasons for the increasing of hydraulic conductivity during the wet-dry cycling.
Desiccation cracks of compacted clay liner might have a great effect on its hydraulic conductivity. During the decrease of its water content, its crack area ratio, length and width will increase. Desiccation cracks can be divided into the major and the minor types. There are obvious differences for the change rate of crack parameters before and after minor cracks appear. Wider cracks can't entirely heal after hydration, which reveals that the wet-dry cycling is irreversible for the compacted clay liner. Development of cracks in the clay can be monitored successfully with the Araldite that was put on the inside wall surface of the test cylinder. The Araldite can also prevent side-leakage. One wet-dry cycling can increase the hydraulic conductivity of the compacted clay liner for nearly two orders in its magnitude. Non-completely-healing cracks and microcracks might be the main reasons for the increasing of hydraulic conductivity during the wet-dry cycling.
2012, 20(3): 403-409.
Research on quantitative evaluation of the compression behavior for reconstituted clays usually provides a reference framework for interpreting the corresponding characteristics of natural sedimentary clays.The intrinsic compression line(ICL) was proposed by Burland in 1990.the void index was introduced for normalizing the compression curves of various reconstituted clays having an initial water content of 1.0~1.5 times(preferably 1.25 times)the liquid limit.the properties of reconstituted clays were also termed ‘intrinsic’ properties since they were inherent to the soil and independent of the natural state.In this paper,extensive oedometer tests are carried out on four different clays.They are reconstituted and extended to 0.7~2.0 times the liquid limits.The test results suggest that the compression behavior for reconstituted clays is in fact not the ‘intrinsic' properties proposed by Burland,which is not only affected by soil liquid limit but also affected by soil initial water content.A modification based on the test data is presented on the expressions of e*100 and C*c defined by Burland.Extensive oedometer test data are also collected on various reconstituted soils with distinct liquid limits and initial water contents to verify the validity and applicability of modified expressions.
Research on quantitative evaluation of the compression behavior for reconstituted clays usually provides a reference framework for interpreting the corresponding characteristics of natural sedimentary clays.The intrinsic compression line(ICL) was proposed by Burland in 1990.the void index was introduced for normalizing the compression curves of various reconstituted clays having an initial water content of 1.0~1.5 times(preferably 1.25 times)the liquid limit.the properties of reconstituted clays were also termed ‘intrinsic’ properties since they were inherent to the soil and independent of the natural state.In this paper,extensive oedometer tests are carried out on four different clays.They are reconstituted and extended to 0.7~2.0 times the liquid limits.The test results suggest that the compression behavior for reconstituted clays is in fact not the ‘intrinsic' properties proposed by Burland,which is not only affected by soil liquid limit but also affected by soil initial water content.A modification based on the test data is presented on the expressions of e*100 and C*c defined by Burland.Extensive oedometer test data are also collected on various reconstituted soils with distinct liquid limits and initial water contents to verify the validity and applicability of modified expressions.
2012, 20(3): 410-418.
The Distinct Element Method(DEM) is widly used in many disciplines and engineering domain. The DEM is developed and improved based on their theories and research realm. So it is possible that the development directions are different. They can use for reference each other. The basic issue of particle fracture is introduced in this paper. It is about particle fracture criterion, the relation between particle fracture and fracture kinetics, the development of macroscopic particle and block impact damage and fracture. These research achievements can benefit to and be reference for rock particle fracture investigation. At the same time, the development abstraction of DEM is introduced in the paper. The basic theory of DEM is also simply introduced as an example of PFC.In the end of paper, the drawbacks about this are specified. The situation of DEM study and application in China is simply commented in engineering geology and geotechnical engineering.
The Distinct Element Method(DEM) is widly used in many disciplines and engineering domain. The DEM is developed and improved based on their theories and research realm. So it is possible that the development directions are different. They can use for reference each other. The basic issue of particle fracture is introduced in this paper. It is about particle fracture criterion, the relation between particle fracture and fracture kinetics, the development of macroscopic particle and block impact damage and fracture. These research achievements can benefit to and be reference for rock particle fracture investigation. At the same time, the development abstraction of DEM is introduced in the paper. The basic theory of DEM is also simply introduced as an example of PFC.In the end of paper, the drawbacks about this are specified. The situation of DEM study and application in China is simply commented in engineering geology and geotechnical engineering.
2012, 20(3): 419-426.
This paper takes into full account of the sedimentary age and environment, soil-type and characteristics and other factors from the geological survey in Suzhou City. It then divides the engineering geological strata groups of soil mass on the eastern plains area. It further identifies the key bearing strata group and weak-sensitive strata. A free piston thin wall sampler and frozen snapping-paste method are used to obtain undisturbed specimens for miro-structure analysis. It uses the analysis of digital images by Scanning Electron Microscope. The comparative studies on the micro-structure properties are carried out to analyze the microstructure type classification under undisturbed natural state, particles' orientation characteristics, eccentricity, orientation probability entropy and other quantitative indicators.that the following results are found. The angle distribution range between the x-axis and the horizontal long axis was relatively concentrated for particles, which means that the degree of anisotropy is relatively low. In addition, shallow marine depositional environments, as well as the transgressive and regressive hydrodynamic effects from Late Quaternary could make the seventh soft layer's distribution probability of eccentricity in(0.6, 1.0) and the orientation probability entropy relatively high. These results are useful to better understand the basic engineering properties of the soft soil in Suzhou city, and to providing important experimental data for establishing the relationship among the sedimentary environment, micro-structure and macro-engineering properties of soils.
This paper takes into full account of the sedimentary age and environment, soil-type and characteristics and other factors from the geological survey in Suzhou City. It then divides the engineering geological strata groups of soil mass on the eastern plains area. It further identifies the key bearing strata group and weak-sensitive strata. A free piston thin wall sampler and frozen snapping-paste method are used to obtain undisturbed specimens for miro-structure analysis. It uses the analysis of digital images by Scanning Electron Microscope. The comparative studies on the micro-structure properties are carried out to analyze the microstructure type classification under undisturbed natural state, particles' orientation characteristics, eccentricity, orientation probability entropy and other quantitative indicators.that the following results are found. The angle distribution range between the x-axis and the horizontal long axis was relatively concentrated for particles, which means that the degree of anisotropy is relatively low. In addition, shallow marine depositional environments, as well as the transgressive and regressive hydrodynamic effects from Late Quaternary could make the seventh soft layer's distribution probability of eccentricity in(0.6, 1.0) and the orientation probability entropy relatively high. These results are useful to better understand the basic engineering properties of the soft soil in Suzhou city, and to providing important experimental data for establishing the relationship among the sedimentary environment, micro-structure and macro-engineering properties of soils.
2012, 20(3): 427-432.
This paper investigates the three-layer structural soft soil that widely exists in Fuzhou Basin. First, the sedimentary features and conventional physical mechanics properties of the three soils are illustrated respectively. Then by means of the resonant column test instrument, a series of dynamic tests are conducted with different consolidation stresses to attain the dynamic damping ratio λ of different structural soft soils under the effect of dynamic load. The relation curve of damping ratio λ and shear strain γ is presented by virtue of numerical analyses to further analyze the differences of test results for different structural soft soils. Tests show that the relation of dynamic damping ratio λ and shear strain γ doesn't have strong correlation with consolidation stresses and the curve λ-γ of three-layer structural soft soil has large difference when the range of shear strain is between 0.00001 and 0.01. The test result will provide reliable data for further understanding the seismic effect of soil layers in Fuzhou Basin, and it is of real significance.
This paper investigates the three-layer structural soft soil that widely exists in Fuzhou Basin. First, the sedimentary features and conventional physical mechanics properties of the three soils are illustrated respectively. Then by means of the resonant column test instrument, a series of dynamic tests are conducted with different consolidation stresses to attain the dynamic damping ratio λ of different structural soft soils under the effect of dynamic load. The relation curve of damping ratio λ and shear strain γ is presented by virtue of numerical analyses to further analyze the differences of test results for different structural soft soils. Tests show that the relation of dynamic damping ratio λ and shear strain γ doesn't have strong correlation with consolidation stresses and the curve λ-γ of three-layer structural soft soil has large difference when the range of shear strain is between 0.00001 and 0.01. The test result will provide reliable data for further understanding the seismic effect of soil layers in Fuzhou Basin, and it is of real significance.
2012, 20(3): 433-439.
The K129 landslide is located on the ancient landslide which lies on the east of meihua village of qingtong town in Zhen'an county, Shaanxi. Due to constructing highway, a high slope was cut in the front of the ancient landslide. The cut volume was of 6.0?04m3.The ancient landslide was relived because no stabilizing measures were adopted in October, 2009.The deformation developed very quickly, and caused the road pavement to heave, the retaining wall to crack. If the whole landslide moved down, not only Xi'an-an'kang highway and Highway 102 were interrupted, but also Qianyou river jammed. The jam would be formed a landslide dam and a lake which would threaten the lives and property of the peoples round the river. In view of the landslide, on the basis of geologic analysis, authors investigate the landslide failure modes. It was found that the formation of landslide control factors was the fragile geologic framework composed by the silty clay mixed stone fragments and phyllite and water-rock reaction. Rainfall was the main factor inducing the landslide. Engineering excavation weakened the locked segment of landslide, accelerated the landslide deformation. Meantime, the characters of the deformation rate and spatial deformation in the landslide were reflected by the displacement monitoring datum and construction feedback information. Namely the landslide belonged to the bedrock interface landslide. The primary character is the back force. The minor one is the foreside pull. According to the study data, the emergency measures, design and construction options were adjusted in time, which ensured that the landslide treatment was completed successfully.
The K129 landslide is located on the ancient landslide which lies on the east of meihua village of qingtong town in Zhen'an county, Shaanxi. Due to constructing highway, a high slope was cut in the front of the ancient landslide. The cut volume was of 6.0?04m3.The ancient landslide was relived because no stabilizing measures were adopted in October, 2009.The deformation developed very quickly, and caused the road pavement to heave, the retaining wall to crack. If the whole landslide moved down, not only Xi'an-an'kang highway and Highway 102 were interrupted, but also Qianyou river jammed. The jam would be formed a landslide dam and a lake which would threaten the lives and property of the peoples round the river. In view of the landslide, on the basis of geologic analysis, authors investigate the landslide failure modes. It was found that the formation of landslide control factors was the fragile geologic framework composed by the silty clay mixed stone fragments and phyllite and water-rock reaction. Rainfall was the main factor inducing the landslide. Engineering excavation weakened the locked segment of landslide, accelerated the landslide deformation. Meantime, the characters of the deformation rate and spatial deformation in the landslide were reflected by the displacement monitoring datum and construction feedback information. Namely the landslide belonged to the bedrock interface landslide. The primary character is the back force. The minor one is the foreside pull. According to the study data, the emergency measures, design and construction options were adjusted in time, which ensured that the landslide treatment was completed successfully.
2012, 20(3): 440-446.
The f5 fault and lamprophyre vein of Jinping Ⅰ Hydropower have an adverse effect to deformation stability and stress transfer of dam foundation. They can seriously affect the stability and safe operation of the dam. This paper investigates the cement grout problems for the f5 fault and lamprophyre vein. It is combined with its engineering geology. It examines the cement-chemical compound grouting technology from grouting materials, grouting method, and field grouting. It evaluates the grouting on the basis of mechanism of cement-chemical compound grouting. The results show that the use of grouting materials can be better irrigation. Construction technology and grouting parameters are reasonable. The permeability of rock has been improved. The wave velocity and deformation modulus of the f5 fault and lamprophyre have a certain degree of improvement. But they still do not meet the design requirements. Optimization proposal has been got from grouting materials, parameters and quality checks on the basis of the grouting evaluation results.
The f5 fault and lamprophyre vein of Jinping Ⅰ Hydropower have an adverse effect to deformation stability and stress transfer of dam foundation. They can seriously affect the stability and safe operation of the dam. This paper investigates the cement grout problems for the f5 fault and lamprophyre vein. It is combined with its engineering geology. It examines the cement-chemical compound grouting technology from grouting materials, grouting method, and field grouting. It evaluates the grouting on the basis of mechanism of cement-chemical compound grouting. The results show that the use of grouting materials can be better irrigation. Construction technology and grouting parameters are reasonable. The permeability of rock has been improved. The wave velocity and deformation modulus of the f5 fault and lamprophyre have a certain degree of improvement. But they still do not meet the design requirements. Optimization proposal has been got from grouting materials, parameters and quality checks on the basis of the grouting evaluation results.
2012, 20(3): 447-452.
How to control of the differential settlement is a key task for the soft soil subgrade in Expressway extension project. This paper examines the experiment section of one expressway extension project in northern China. The finite element calculation is carried out for the deformation of widening soft soil subgrade. The Abaqus software is used. The calculation results are in accordance with the deformation monitoring information at field tests. These results conformably demonstrate the deformation characteristics that widening subgrade presents larger settlement rate in the initial stage of embankment filling. But the old subgrade has obvious additional settlement. The basin-curve of settlement appears in the bottom of widening subgrade. The differential settlement between the new and old subgrade is one of the main reasons that inducing longitudinal subgrade cracks. The foundation soil near the bottom of the composite foundation of prestressed thin-wall concrete (PTC) pile with cap presents obvious extrusion deformation in horizontal directions, which shows that PTC pile tip should be placed at effective bearing stratum with relatively high capacity.
How to control of the differential settlement is a key task for the soft soil subgrade in Expressway extension project. This paper examines the experiment section of one expressway extension project in northern China. The finite element calculation is carried out for the deformation of widening soft soil subgrade. The Abaqus software is used. The calculation results are in accordance with the deformation monitoring information at field tests. These results conformably demonstrate the deformation characteristics that widening subgrade presents larger settlement rate in the initial stage of embankment filling. But the old subgrade has obvious additional settlement. The basin-curve of settlement appears in the bottom of widening subgrade. The differential settlement between the new and old subgrade is one of the main reasons that inducing longitudinal subgrade cracks. The foundation soil near the bottom of the composite foundation of prestressed thin-wall concrete (PTC) pile with cap presents obvious extrusion deformation in horizontal directions, which shows that PTC pile tip should be placed at effective bearing stratum with relatively high capacity.
2012, 20(3): 453-458.
More complicated geological conditions can be encountered in tunnel construction. Flexible support system composing of anchors, sprayed concrete and steel ribs is widely employed in road tunnels with poor surrounding rock conditions such as the grade V surrounding rock. The steel rib is the skeleton and the main bearing structure of the flexible support system. Its pressure distribution state is one of the key factors for controlling the stability of temporary support system in advance. The pressure varying characteristics between the joint areas of steel ribs and surrounding rock can greatly reflect the surrounding rock state. These areas are the crown, the jointed points and the feet of steel ribs..According to the varying characteristics of such complicated pressure states in the grade V surrounding rock after excavation of road tunnel, safety control standards of tunnel construction process are adopted as the key factor of surrounding rock deformation. The pressure sensors are used for monitoring its variation on steel ribs in the Bangchuigou road tunnel. With a large number of monitoring data analysis, the following pre-conclusions can be obtained: (1)Pressure on the steel ribs is not symmetric. The parameters of temporary support system should be optimized in time according to the surrounding rock pressure distribution.(2)Within four meters between tunnel face and monitoring section, the pressure on steel rib at arch centering increases significantly. The stiffness of the jointed steel rib as a whole should be properly kept in high state.(3)the pressure on steel rib at the joints and feet of steel ribs also greatly changes, where the weakness parts of steel rib support system are .So the stiffness and stability should be fully considered at design stage for assuring the safety of tunnel construction. These results not only are of theoretical and constructional importance for tunnel projects, but also can help us improve g our tunnel design for other similar studies.
More complicated geological conditions can be encountered in tunnel construction. Flexible support system composing of anchors, sprayed concrete and steel ribs is widely employed in road tunnels with poor surrounding rock conditions such as the grade V surrounding rock. The steel rib is the skeleton and the main bearing structure of the flexible support system. Its pressure distribution state is one of the key factors for controlling the stability of temporary support system in advance. The pressure varying characteristics between the joint areas of steel ribs and surrounding rock can greatly reflect the surrounding rock state. These areas are the crown, the jointed points and the feet of steel ribs..According to the varying characteristics of such complicated pressure states in the grade V surrounding rock after excavation of road tunnel, safety control standards of tunnel construction process are adopted as the key factor of surrounding rock deformation. The pressure sensors are used for monitoring its variation on steel ribs in the Bangchuigou road tunnel. With a large number of monitoring data analysis, the following pre-conclusions can be obtained: (1)Pressure on the steel ribs is not symmetric. The parameters of temporary support system should be optimized in time according to the surrounding rock pressure distribution.(2)Within four meters between tunnel face and monitoring section, the pressure on steel rib at arch centering increases significantly. The stiffness of the jointed steel rib as a whole should be properly kept in high state.(3)the pressure on steel rib at the joints and feet of steel ribs also greatly changes, where the weakness parts of steel rib support system are .So the stiffness and stability should be fully considered at design stage for assuring the safety of tunnel construction. These results not only are of theoretical and constructional importance for tunnel projects, but also can help us improve g our tunnel design for other similar studies.
2012, 20(3): 459-465.
Dewatering for foundation pit excavation is usually used. This method can change the engineering properties of soils around the pit. Consequently, the buildings around the pit can be affected. Differential settlements and cracking in the buildings can occur. Dewatering at the pit of the West Railway Station in Jinan made significant effects to subgrade of the Beijing-Shanghai High-Speed Railway Line. This paper examines this problem. The effect of dewatering at the large station pit to its surroundings is not yet fully understood theoretically. This paper studies the effect of the foundation pit to the nearby composite foundation settlement. It uses the section DIK419+250 Jinan West Railway Station. Settlement plates are used to monitor the settlement of the subgrade surface. Settlement devices at different ground depths are used to monitor the settlement of the subgrade at depths. The cross-sectional profile device is used to monitor the changes along the cross profile of the subgrade. The monitored results are used to examine the effects of the dewatering on the subgrade surface, its depth soils and its cross profiles. Furthermore, according to the site conditions, the paper uses the finite element analysis method to numerically simulate the on-site monitored results. The comparative studies have the following conclusions: (1)the improvement of the composite foundation can reduce the effect of the dewatering; (2)the area with variable pile foundation lengths can be largely affected by the dewatering; and (3)pit dewatering can have larger effect to the subgrade settlement than the sub-soils.
Dewatering for foundation pit excavation is usually used. This method can change the engineering properties of soils around the pit. Consequently, the buildings around the pit can be affected. Differential settlements and cracking in the buildings can occur. Dewatering at the pit of the West Railway Station in Jinan made significant effects to subgrade of the Beijing-Shanghai High-Speed Railway Line. This paper examines this problem. The effect of dewatering at the large station pit to its surroundings is not yet fully understood theoretically. This paper studies the effect of the foundation pit to the nearby composite foundation settlement. It uses the section DIK419+250 Jinan West Railway Station. Settlement plates are used to monitor the settlement of the subgrade surface. Settlement devices at different ground depths are used to monitor the settlement of the subgrade at depths. The cross-sectional profile device is used to monitor the changes along the cross profile of the subgrade. The monitored results are used to examine the effects of the dewatering on the subgrade surface, its depth soils and its cross profiles. Furthermore, according to the site conditions, the paper uses the finite element analysis method to numerically simulate the on-site monitored results. The comparative studies have the following conclusions: (1)the improvement of the composite foundation can reduce the effect of the dewatering; (2)the area with variable pile foundation lengths can be largely affected by the dewatering; and (3)pit dewatering can have larger effect to the subgrade settlement than the sub-soils.
2012, 20(3): 466-470.
The secondary consolidation coefficient has been considered constant in engineering. However, there are many research findings that the secondary consolidation coefficient is not a constant by means of laboratory test. The coefficient can change with the time. The secondary consolidation coefficient has nothing to do with the consolidation pressure. But many tests also show that the secondary consolidation coefficient has some correlations with the consolidation pressure, compression index, moisture content and plasticity index. This paper studies the secondary consolidation properties of soft cohesive soil in Beijing plain. It finds and analyses these relations. The results show that for the over-consolidated soil, the coefficient of secondary consolidation increases as the load increases. For the normal-consolidated soil, it decreases as the load increases. It also keeps a linear increase with moisture content and plasticity index. The ratio of Cα/Cc is a constant.
The secondary consolidation coefficient has been considered constant in engineering. However, there are many research findings that the secondary consolidation coefficient is not a constant by means of laboratory test. The coefficient can change with the time. The secondary consolidation coefficient has nothing to do with the consolidation pressure. But many tests also show that the secondary consolidation coefficient has some correlations with the consolidation pressure, compression index, moisture content and plasticity index. This paper studies the secondary consolidation properties of soft cohesive soil in Beijing plain. It finds and analyses these relations. The results show that for the over-consolidated soil, the coefficient of secondary consolidation increases as the load increases. For the normal-consolidated soil, it decreases as the load increases. It also keeps a linear increase with moisture content and plasticity index. The ratio of Cα/Cc is a constant.
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