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Editor Work2012 Vol. 20, No. 2
Previous Issue
2012, 20(2): 145-151.
Abstract
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Research on slope deformation and failure process and landslide prediction method has been undertaken freqeuently since Saito developed the landslide prediction and forecasting method with help of creep test in 1960s. Dozens of models and methods for landslide prediction and forecasting have been put forward. With the increasing monitoring work on slope deformation and increasing available data, many kinds of displacement-time curves have been proposed. Many problems such as the types and features of slope displacement-time curves and the mechanic conditions forming the curves must be regarded as the most basic scientific problems. Theyhave to be answered and solved when landslide early warning and prediction are being carried out. This paper summarizes the landslide deformation and failure mechanisms and their corresponding displacement-time curves. With the aid of rheological test, three types of landslide deformation and failure processes are proposed. They are thehe steady type, the gradual change type and the sudden failure type. Their corresponding mechanic conditions are also studied. In the view of micromechanics, the macro deformation and failure of a slope are mainly attributed to the flow and micro rupture of rock and soil in microscopic scale. The flow and micro rupture can play different roles in slopes with different lithology or in different deformation phases of a slope.
Research on slope deformation and failure process and landslide prediction method has been undertaken freqeuently since Saito developed the landslide prediction and forecasting method with help of creep test in 1960s. Dozens of models and methods for landslide prediction and forecasting have been put forward. With the increasing monitoring work on slope deformation and increasing available data, many kinds of displacement-time curves have been proposed. Many problems such as the types and features of slope displacement-time curves and the mechanic conditions forming the curves must be regarded as the most basic scientific problems. Theyhave to be answered and solved when landslide early warning and prediction are being carried out. This paper summarizes the landslide deformation and failure mechanisms and their corresponding displacement-time curves. With the aid of rheological test, three types of landslide deformation and failure processes are proposed. They are thehe steady type, the gradual change type and the sudden failure type. Their corresponding mechanic conditions are also studied. In the view of micromechanics, the macro deformation and failure of a slope are mainly attributed to the flow and micro rupture of rock and soil in microscopic scale. The flow and micro rupture can play different roles in slopes with different lithology or in different deformation phases of a slope.
2012, 20(2): 152-159.
Image grid cell is a widely used mapping unit type in GIS-based geohazard assessment. Values of each controlling factor should be calculated and endowed to grids. Risk levels can be determined through overlay analysis. However, due to the lack of quantitative computational model, the determination of grid size is largely dependent on expert experience. Taking Enshi City as an example, this paper analyzes the influence mechanism of grid sizes on the most commonly used controlling factors. The results can provide scientific basis for the determination of grid size.
Image grid cell is a widely used mapping unit type in GIS-based geohazard assessment. Values of each controlling factor should be calculated and endowed to grids. Risk levels can be determined through overlay analysis. However, due to the lack of quantitative computational model, the determination of grid size is largely dependent on expert experience. Taking Enshi City as an example, this paper analyzes the influence mechanism of grid sizes on the most commonly used controlling factors. The results can provide scientific basis for the determination of grid size.
2012, 20(2): 160-169.
The ground fissures in Longyao County are the typical surface disaster in North China region. They not only caused eroding, collapsing, extension fracturing, faulting, cracking and other geological disasters on the earth’s surface, but also caused severe economic losses in the local agricultural production, engineering construction and the lives of the people. This paper aims to reveal their genetic nature. It is based on geological investigation, monitoring and measuring, trenching, physical exploration. It studies the development characteristics of the Longyao ground fissures. They include the planes, profiles, deep and activity aspects. The paper summarizes the laws of ground fissures. Finally the ground fissure mechanism is analyzed from their crack-pregnant environment, crack-opening conditions and cracking process.the study concludes that: (1)Longyao ground fissures expose in a dozen villages of more than 30km long. They extend towards NWW and NEE which are concordant with the direction of Longyao fault system. Their periodicities are consist of opening, closing, slowly cracking and suddenly cracking periods.(2)Longyao ground fissures are controlled by the faults zone. The conditions such as deep structure, faulted structure and structural landform provide the ground fissures with crack-pregnant environment in the area. The crack-pregnant environment has through three stages: stress accumulation and fractured zone formation.(3)Faulting is the foundation of ground cracking. The groundwater exploitation and surface infiltration also are the important factors.(4)the process of Longyao ground fissures is heterogenous temporally and spatially. From the present investigation and study, the ground fissures are in active period in the area.
The ground fissures in Longyao County are the typical surface disaster in North China region. They not only caused eroding, collapsing, extension fracturing, faulting, cracking and other geological disasters on the earth’s surface, but also caused severe economic losses in the local agricultural production, engineering construction and the lives of the people. This paper aims to reveal their genetic nature. It is based on geological investigation, monitoring and measuring, trenching, physical exploration. It studies the development characteristics of the Longyao ground fissures. They include the planes, profiles, deep and activity aspects. The paper summarizes the laws of ground fissures. Finally the ground fissure mechanism is analyzed from their crack-pregnant environment, crack-opening conditions and cracking process.the study concludes that: (1)Longyao ground fissures expose in a dozen villages of more than 30km long. They extend towards NWW and NEE which are concordant with the direction of Longyao fault system. Their periodicities are consist of opening, closing, slowly cracking and suddenly cracking periods.(2)Longyao ground fissures are controlled by the faults zone. The conditions such as deep structure, faulted structure and structural landform provide the ground fissures with crack-pregnant environment in the area. The crack-pregnant environment has through three stages: stress accumulation and fractured zone formation.(3)Faulting is the foundation of ground cracking. The groundwater exploitation and surface infiltration also are the important factors.(4)the process of Longyao ground fissures is heterogenous temporally and spatially. From the present investigation and study, the ground fissures are in active period in the area.
2012, 20(2): 170-182.
Nowadays, landslide risk management is an effective way for disaster prevention and mitigation, and has been widely used in the world. For the development of the county landslides risk management information system(CLRMIS),the paper discusses the characteristics, requirements and technical processes of the CLRMIS,constructs the system structure and functional modules, and develops the system by using geographic information techniques. We chose Ningqiang County, Shaanxi Province as the area for testing CLRMIS.Our work emphasized on the hazard analysis, consequence analysis, and the risk evaluation. Based on the CLRMIS,the county area’s landslides hazard and consequence were studied respectively by using information value method and weighted superposition method, the individual’s were studied by using expert scoring method. The landslides general risk, dynamic risk and forecasting were evaluated based on the qualitative risk analysis(QRA)matrix. The results show that the CLRMIS is able to provide an effective support for the landslides management, risk analysis, and prevention and mitigation to local authorities.
Nowadays, landslide risk management is an effective way for disaster prevention and mitigation, and has been widely used in the world. For the development of the county landslides risk management information system(CLRMIS),the paper discusses the characteristics, requirements and technical processes of the CLRMIS,constructs the system structure and functional modules, and develops the system by using geographic information techniques. We chose Ningqiang County, Shaanxi Province as the area for testing CLRMIS.Our work emphasized on the hazard analysis, consequence analysis, and the risk evaluation. Based on the CLRMIS,the county area’s landslides hazard and consequence were studied respectively by using information value method and weighted superposition method, the individual’s were studied by using expert scoring method. The landslides general risk, dynamic risk and forecasting were evaluated based on the qualitative risk analysis(QRA)matrix. The results show that the CLRMIS is able to provide an effective support for the landslides management, risk analysis, and prevention and mitigation to local authorities.
2012, 20(2): 189-194.
Landslide hazard control is a systematic engineering work. Thus the effect evaluations of countermeasure to landslide hazards are more complicated. Based on the analysis of a great deal of site investigation and comparative study, this paper makes an exploratory research on the effect evaluation by the principle of system analysis. Combined with quantitative and qualitative evaluation method, this paper proposes an assessment approach with multi-levels and multi-factors. The index systems of each sub-goal are established according to the whole process of landslide hazard control. They include survey, design, construction, and monitoring work. The comprehensive evaluation model is called as the "assessment effect of index(AEI)".It can ensure that the evaluation approach of countermeasure efficiency for landslide hazard is valuable. It is established by the results of each sub-goal and the analysis of "slope instability index(SII)".The application case shows that this approach can obtain a comprehensive analysis and effect evaluation of landslide hazard control.
Landslide hazard control is a systematic engineering work. Thus the effect evaluations of countermeasure to landslide hazards are more complicated. Based on the analysis of a great deal of site investigation and comparative study, this paper makes an exploratory research on the effect evaluation by the principle of system analysis. Combined with quantitative and qualitative evaluation method, this paper proposes an assessment approach with multi-levels and multi-factors. The index systems of each sub-goal are established according to the whole process of landslide hazard control. They include survey, design, construction, and monitoring work. The comprehensive evaluation model is called as the "assessment effect of index(AEI)".It can ensure that the evaluation approach of countermeasure efficiency for landslide hazard is valuable. It is established by the results of each sub-goal and the analysis of "slope instability index(SII)".The application case shows that this approach can obtain a comprehensive analysis and effect evaluation of landslide hazard control.
2012, 20(2): 195-203.
The total amount of the loose masses due to collapses and landslides by Wenchuan Earthquake reached about 28?108m3.the loose masses can provide abundant materials for debris flows for long term.The critical rainfall has decreased significantly.The debris flow events have occurred at high frequency and in group.Their discharges have increased.Blocking of main rivers by debris flows have occurred more frequently post the earthquake and led serious secondary disasters in the quake-hit areas.In order to evaluate the probability of blocking river by debris flow,the basic data of debris flow gullies are obtained on the basis of field investigation and scale in different precipitation frequency according to a hydrological model.Then based on the above data and the differentiation formula of debris flow blocking river,this paper assesses the degree of debris flow blocking main river of the study area.It then defines the threshold value of the differentiation formula combined with debris flows that have occurred in the study area and blocked rivers.As a result,it can be used to determine the probability of debris blocking river more accurately.Seven debris flow gullies of the study area are evaluated at different precipitation frequencies.The results show that the debris flow of Niumian gully and Guanshan gully can block the Minjing river under the 50 years return period precipitation.The debris flow of Shaofang gully,Hongchun Gully and Mozi gully can block the Minjing river under the 10 years return period precipitation.The debris flow of Er gully and Taiping gully can block the Minjing river under the 5 years return period precipitation.The assessment result agrees with the phenomena of field investigation and can provide scientific supports for the prevention,elusion and mitigation of debris flow hazards and reconstruction project in the earthquake area.
The total amount of the loose masses due to collapses and landslides by Wenchuan Earthquake reached about 28?108m3.the loose masses can provide abundant materials for debris flows for long term.The critical rainfall has decreased significantly.The debris flow events have occurred at high frequency and in group.Their discharges have increased.Blocking of main rivers by debris flows have occurred more frequently post the earthquake and led serious secondary disasters in the quake-hit areas.In order to evaluate the probability of blocking river by debris flow,the basic data of debris flow gullies are obtained on the basis of field investigation and scale in different precipitation frequency according to a hydrological model.Then based on the above data and the differentiation formula of debris flow blocking river,this paper assesses the degree of debris flow blocking main river of the study area.It then defines the threshold value of the differentiation formula combined with debris flows that have occurred in the study area and blocked rivers.As a result,it can be used to determine the probability of debris blocking river more accurately.Seven debris flow gullies of the study area are evaluated at different precipitation frequencies.The results show that the debris flow of Niumian gully and Guanshan gully can block the Minjing river under the 50 years return period precipitation.The debris flow of Shaofang gully,Hongchun Gully and Mozi gully can block the Minjing river under the 10 years return period precipitation.The debris flow of Er gully and Taiping gully can block the Minjing river under the 5 years return period precipitation.The assessment result agrees with the phenomena of field investigation and can provide scientific supports for the prevention,elusion and mitigation of debris flow hazards and reconstruction project in the earthquake area.
2012, 20(2): 204-212.
The"5?12"Wenchuan earthquake induced many secondary geological disasters.The Hongtupo landslide in southern Gansu took place in large-scale collapse and cracks during the earthquake.If the landslide was moved as a whole,then it would form a dammed lake.It seriously threats the safety of eighty hundreds people in place below the landslide.So,it is very important to adequately understand stability of the landslide and take effective emergency measures.Based on the geological environment where landslide located,a systematic research on characteristics and forming mechanism of the Hongtupo landside at Southern Gansu was achieved.The used methods includedregional geological investigation,measurement of micro physiognomy and failure and geophysical reconnaissance survey.The research results show that this landslide has the characteristics of remarkable classification and partitioning.The key elements of inducing this landslide to be revivable are rainfall,earthquake,river degradation and poor rock and soil mass engineering geological properties.Based on the landslide forming mechanism,using the method of transfer coefficient and so on,the stability states were evaluated by combination of qualitative and quantitative analysis on the conditions of natural state,rainfall and earthquake,respectively.The integrated control measures of prestressed anchor cable frame,blocking dam,draining and protective wall are put forward.
The"5?12"Wenchuan earthquake induced many secondary geological disasters.The Hongtupo landslide in southern Gansu took place in large-scale collapse and cracks during the earthquake.If the landslide was moved as a whole,then it would form a dammed lake.It seriously threats the safety of eighty hundreds people in place below the landslide.So,it is very important to adequately understand stability of the landslide and take effective emergency measures.Based on the geological environment where landslide located,a systematic research on characteristics and forming mechanism of the Hongtupo landside at Southern Gansu was achieved.The used methods includedregional geological investigation,measurement of micro physiognomy and failure and geophysical reconnaissance survey.The research results show that this landslide has the characteristics of remarkable classification and partitioning.The key elements of inducing this landslide to be revivable are rainfall,earthquake,river degradation and poor rock and soil mass engineering geological properties.Based on the landslide forming mechanism,using the method of transfer coefficient and so on,the stability states were evaluated by combination of qualitative and quantitative analysis on the conditions of natural state,rainfall and earthquake,respectively.The integrated control measures of prestressed anchor cable frame,blocking dam,draining and protective wall are put forward.
2012, 20(2): 213-221.
The Wenchuan Earthquake triggered a large number of collapses,landslides and other secondary disasters which caused serious loss of life and property.Among them,the mountain collapse in the back of Panda Garden rearing sheds located in Wolong was a typical shock-triggered damage.Because the collapse region is relatively close to the focal point of the earthquake,the seismic action is a master external factor affecting collapse damage.The topography and rock mass structure are the most critical factors in the internal factors.Based on the field investigation and laboratory tests,the slope dynamic response characteristics is simulated using the calculation software of discrete element to obtain the collapse failure mechanism,advantage-shattering region and controlling factors.The simulation results are showed as follows: (1)the combined action of the tension,compression and shear which are caused by coupling of primary wave and secondary wave, is the direct driving force of the collapse damage.(2)in the early stage of seismic action,the first tensile failure generates in the group of tectonic joints with near steep dip angle and forms a wedge-shaped crack extending from the outside to the inside.Later stage,because the second tectonic group of joints and bedding plane trend to outside of slope,the collapse instability of the shattered and cracked rock blocks occurs in the ways of dumping and slippage outside.The slope looks like curved shape and produce overall instability.(3)Due to inertia effect of the earthquake,the collapse of the shattered and cracked rock in the surface starts with some initial velocity.This is one of the main reasons why earthquake-induced collapse has larger destructive influence scope.The prevention for the potential collapse damage of similar slope should be mainly based on reinforcement of steep structural plane,combining the strengthening of the slope shoulder support.
The Wenchuan Earthquake triggered a large number of collapses,landslides and other secondary disasters which caused serious loss of life and property.Among them,the mountain collapse in the back of Panda Garden rearing sheds located in Wolong was a typical shock-triggered damage.Because the collapse region is relatively close to the focal point of the earthquake,the seismic action is a master external factor affecting collapse damage.The topography and rock mass structure are the most critical factors in the internal factors.Based on the field investigation and laboratory tests,the slope dynamic response characteristics is simulated using the calculation software of discrete element to obtain the collapse failure mechanism,advantage-shattering region and controlling factors.The simulation results are showed as follows: (1)the combined action of the tension,compression and shear which are caused by coupling of primary wave and secondary wave, is the direct driving force of the collapse damage.(2)in the early stage of seismic action,the first tensile failure generates in the group of tectonic joints with near steep dip angle and forms a wedge-shaped crack extending from the outside to the inside.Later stage,because the second tectonic group of joints and bedding plane trend to outside of slope,the collapse instability of the shattered and cracked rock blocks occurs in the ways of dumping and slippage outside.The slope looks like curved shape and produce overall instability.(3)Due to inertia effect of the earthquake,the collapse of the shattered and cracked rock in the surface starts with some initial velocity.This is one of the main reasons why earthquake-induced collapse has larger destructive influence scope.The prevention for the potential collapse damage of similar slope should be mainly based on reinforcement of steep structural plane,combining the strengthening of the slope shoulder support.
2012, 20(2): 222-227.
Compared to general high slopes,there is an obvious difference in the material composition,boundary condition and mechanical character for deposit slopes.Because of the obvious discontinuity character of deposit slopes in terms of deformation and failure,it is difficult to reveal its failure mode and process for conventional stability analysis method.The discrete element method(DEM)can provide an optimum solution to problems such as deformation and failure of discontinuity.Firstly,based on a large-scale complex slope in debris deposit,a numerical test is carried to simulate triaxial test of deposit soil.Micromechanics parameters are determined through comparison to the laboratory test results.A general study on its failure mechanics was carried out using DEM.Failure mode and deformation process were also involved.The results show: the slope before excavation is stability.There are two potential slides mass on the upside of slope after first step of excavation showing deep sliding along bedrock underlying debris deposit.There is an obvious slide mass at the bottom of slope after second step of excavation.Its failure will speed deformation and sliding of two potential slides.For the whole slope in debris deposit,its failure mechanics mainly shows in a gradual deformation and failure mode along contact surface from bottom to upside.
Compared to general high slopes,there is an obvious difference in the material composition,boundary condition and mechanical character for deposit slopes.Because of the obvious discontinuity character of deposit slopes in terms of deformation and failure,it is difficult to reveal its failure mode and process for conventional stability analysis method.The discrete element method(DEM)can provide an optimum solution to problems such as deformation and failure of discontinuity.Firstly,based on a large-scale complex slope in debris deposit,a numerical test is carried to simulate triaxial test of deposit soil.Micromechanics parameters are determined through comparison to the laboratory test results.A general study on its failure mechanics was carried out using DEM.Failure mode and deformation process were also involved.The results show: the slope before excavation is stability.There are two potential slides mass on the upside of slope after first step of excavation showing deep sliding along bedrock underlying debris deposit.There is an obvious slide mass at the bottom of slope after second step of excavation.Its failure will speed deformation and sliding of two potential slides.For the whole slope in debris deposit,its failure mechanics mainly shows in a gradual deformation and failure mode along contact surface from bottom to upside.
2012, 20(2): 228-233.
This paper is based on a comprehensive analysis of geomaterials parameters. It introduces the interval analysis model for stability assesment of slopes. By referring interval mathematics idea, the interval limited equilibrium method is used to derive the interval minimum safety factor of slopes. Based on this foundation, the paper carries out the non-probabilistic reliability analysis of slope stabilities.
This paper is based on a comprehensive analysis of geomaterials parameters. It introduces the interval analysis model for stability assesment of slopes. By referring interval mathematics idea, the interval limited equilibrium method is used to derive the interval minimum safety factor of slopes. Based on this foundation, the paper carries out the non-probabilistic reliability analysis of slope stabilities.
2012, 20(2): 234-241.
Seismic liquefaction problems of road embankment slope are involved in two different fields which are geotechnical engineering and engineering earthquake.Therefore,it’s a cross topic of slope engineering and sand liquefaction.By means of Finn constitutive model,the dynamical stability and liquefaction failure mechanics of road embankment slope which is made up of fill,sand soil and gravel soil under natural seismic loading are simulated with finite difference method.The following results are obtained.Firstly the deformation and failure of road embankment slope under seismic loading are caused by subgrade sand liquefaction which results in the effective stress decreasing rapidly.Secondly the accumulation and dissipation of pore water pressure not only related to earthquake record sequence,but also have a close relation with the position and depth of saturation sand.Thirdly the ground distortion and destruction mostly appears as two aspects which are seismic subsidence at the top of embankment and uplift at the base of slope.Lastly the under-ground deformation and failure principally include shear failure of slope soil mass and lateral spreading of the deep layer induced by sand liquefaction.
Seismic liquefaction problems of road embankment slope are involved in two different fields which are geotechnical engineering and engineering earthquake.Therefore,it’s a cross topic of slope engineering and sand liquefaction.By means of Finn constitutive model,the dynamical stability and liquefaction failure mechanics of road embankment slope which is made up of fill,sand soil and gravel soil under natural seismic loading are simulated with finite difference method.The following results are obtained.Firstly the deformation and failure of road embankment slope under seismic loading are caused by subgrade sand liquefaction which results in the effective stress decreasing rapidly.Secondly the accumulation and dissipation of pore water pressure not only related to earthquake record sequence,but also have a close relation with the position and depth of saturation sand.Thirdly the ground distortion and destruction mostly appears as two aspects which are seismic subsidence at the top of embankment and uplift at the base of slope.Lastly the under-ground deformation and failure principally include shear failure of slope soil mass and lateral spreading of the deep layer induced by sand liquefaction.
2012, 20(2): 242-248.
This paper is based on a large number of secondary geological disasters induced by the Wenchuan Earthquake. It designs and completes a large-scale shaking table model test of slopes with the scale of 1: 100.It discusses the design of similarity relation and the model, sensor layout, process of model construction as well as the seismic wave loading system. The results show that the model slopes have amplification effect to the input dynamic load. Upward along with the slope surfaces, the PGA amplification coefficients have a rise tendency and some rhythmic. The variation law of rhythmic is affected by the lithology of slopes, combination of structural surface and vibration direction of the dynamic loads. Coefficients of the PGA amplification along surface of slopes are significantly greater for the vibration direction of dynamic load to horizontal(X)than for the direction of dynamic load to vertical(Z),which shows that the dynamic response of slopes is stronger when the vibration direction X.The PGA amplification coefficients in the vertical direction of the slope body are amplified linearly. They in the horizontal direction change in rhythm. The results can help to understand the dynamic response rules of steep stratified rock slopes in the effect of different kinds of dynamic loads, and provide a basis to study the mechanism of deformation and instability of slopes under earthquake and the design of anti-earthquake structure.
This paper is based on a large number of secondary geological disasters induced by the Wenchuan Earthquake. It designs and completes a large-scale shaking table model test of slopes with the scale of 1: 100.It discusses the design of similarity relation and the model, sensor layout, process of model construction as well as the seismic wave loading system. The results show that the model slopes have amplification effect to the input dynamic load. Upward along with the slope surfaces, the PGA amplification coefficients have a rise tendency and some rhythmic. The variation law of rhythmic is affected by the lithology of slopes, combination of structural surface and vibration direction of the dynamic loads. Coefficients of the PGA amplification along surface of slopes are significantly greater for the vibration direction of dynamic load to horizontal(X)than for the direction of dynamic load to vertical(Z),which shows that the dynamic response of slopes is stronger when the vibration direction X.The PGA amplification coefficients in the vertical direction of the slope body are amplified linearly. They in the horizontal direction change in rhythm. The results can help to understand the dynamic response rules of steep stratified rock slopes in the effect of different kinds of dynamic loads, and provide a basis to study the mechanism of deformation and instability of slopes under earthquake and the design of anti-earthquake structure.
2012, 20(2): 249-258.
The unexpected strong 5.12 Wenchuan Earthquake caused great economic losses and casualties and affected a large area of Sichuan.After the Wenchuan Earthquake,there were severe secondary geological disasters on the highway from Yingxiu to Wolong.the traffic was usually snarled,which influenced the highway safety operation and reconstruction seriously.What’s more,the post-earthquake collapses are a secondary geological disaster with the wide distribution,severe shatter and large potential threat under the action of strong earthquake.This paper analyzes the formation mechanism on post-earthquake collapses in depth.It takes the highway from Yingxiu to Wolong with more post-earthquake collapses as the research object.It combines with predecessors’ achievements on Wenchuan Earthquake.It is based on the detailed survey about the post-earthquake collapses of slopes near the sides of the highway from Yingxiu to Wolong and 115 profiles.There are four stages of post-earthquake collapses from start to finish.Namely,they are the original structure,potential variable body,shattering rock and collapse.On this basis,the formation mechanism on the post-earthquake collapses of highway slopes can be described as four models including shatter-slip collapse,shatter-dump collapse,shatter-burst collapse and shatter-offset collapse.Because of the complex rock mass structure,there are usually two or three collapse formation mechanisms with a certain way together in the collapse disasters and the formation mechanisms change from one to another during the constant process of evolution and development.However,among them,there is one mechanism which first happed as the major in the collapse.These reveal that the mechanical mechanism of the slope rock mass changes, and determines the final damage forms and features of post-earthquake collapses.The paper makes expatiation of their formation mechanisms.These results provide a powerful reference for highway reconstruction and disaster prevention and mitigation.At the same time they also provide the technical support for such the problems including disaster reduction countermeasures of transportation infrastructure under the influence of the earthquake and the methods for dealing with to clear the road blocked by the collapse,highway slope collapse disasters prevention in the mountainous area and earthquake disaster prevention highway recovery.
The unexpected strong 5.12 Wenchuan Earthquake caused great economic losses and casualties and affected a large area of Sichuan.After the Wenchuan Earthquake,there were severe secondary geological disasters on the highway from Yingxiu to Wolong.the traffic was usually snarled,which influenced the highway safety operation and reconstruction seriously.What’s more,the post-earthquake collapses are a secondary geological disaster with the wide distribution,severe shatter and large potential threat under the action of strong earthquake.This paper analyzes the formation mechanism on post-earthquake collapses in depth.It takes the highway from Yingxiu to Wolong with more post-earthquake collapses as the research object.It combines with predecessors’ achievements on Wenchuan Earthquake.It is based on the detailed survey about the post-earthquake collapses of slopes near the sides of the highway from Yingxiu to Wolong and 115 profiles.There are four stages of post-earthquake collapses from start to finish.Namely,they are the original structure,potential variable body,shattering rock and collapse.On this basis,the formation mechanism on the post-earthquake collapses of highway slopes can be described as four models including shatter-slip collapse,shatter-dump collapse,shatter-burst collapse and shatter-offset collapse.Because of the complex rock mass structure,there are usually two or three collapse formation mechanisms with a certain way together in the collapse disasters and the formation mechanisms change from one to another during the constant process of evolution and development.However,among them,there is one mechanism which first happed as the major in the collapse.These reveal that the mechanical mechanism of the slope rock mass changes, and determines the final damage forms and features of post-earthquake collapses.The paper makes expatiation of their formation mechanisms.These results provide a powerful reference for highway reconstruction and disaster prevention and mitigation.At the same time they also provide the technical support for such the problems including disaster reduction countermeasures of transportation infrastructure under the influence of the earthquake and the methods for dealing with to clear the road blocked by the collapse,highway slope collapse disasters prevention in the mountainous area and earthquake disaster prevention highway recovery.
2012, 20(2): 259-265.
The geological condition of a high and steep slope can be complex. Its weak structural planes can well develop. The excavated height and ratio are high. The excavated faces are many for the sake of the space of the deformation. There are many failure evidences at the slope. Based on investigation of engineering geological conditions, this paper examines the slide plane feature and location of a large scale landslide on a highway. It analyzes the development process and stability status of the landslide. According to the borehole data, the rock mass and sliding surface parameters are obtained. Combining with inverse computation of parameters, the sliding surface’s c and φ values are obtained. Finally under the condition of abnormal(rainstorm) condition, the safety factor of the landslide is found to be 0.91.The value shows that when facing with a long heavy rain, the landslide can be further developed. It needs timely treatment. This paper presents the corresponding control and design measures. They include a) treating the landslide by reduce-loading and b) installing pre-stressed anchor piles in the platform level position. On the basis of slope failure in the process and mechanisms qualitative analysis, this paper uses the discrete element program UDEC to carry out the numerical simulation of landslide. Anti-slide piles with prestressed cables can be effective when they are used to against the failure of the slope. In terms of the known sliding plane, the UDEC is used to simulate the excavation and support of the landslide.the comparative analysis of the landslide displacement before and after reinforcement shows that the anti-slide piles with prestressed cable are safe and effective scheme to the landslide. Comparison shows that the anti-slide pile with prestressed anchor cable has many advantages over the anti-slide pile without prestressed anchor cable. For instance, it changes the stress of the traditional anti-slide pile, changes the cantilever beam into the species simply supported beam, and changes the passive support into active support,and so on.
The geological condition of a high and steep slope can be complex. Its weak structural planes can well develop. The excavated height and ratio are high. The excavated faces are many for the sake of the space of the deformation. There are many failure evidences at the slope. Based on investigation of engineering geological conditions, this paper examines the slide plane feature and location of a large scale landslide on a highway. It analyzes the development process and stability status of the landslide. According to the borehole data, the rock mass and sliding surface parameters are obtained. Combining with inverse computation of parameters, the sliding surface’s c and φ values are obtained. Finally under the condition of abnormal(rainstorm) condition, the safety factor of the landslide is found to be 0.91.The value shows that when facing with a long heavy rain, the landslide can be further developed. It needs timely treatment. This paper presents the corresponding control and design measures. They include a) treating the landslide by reduce-loading and b) installing pre-stressed anchor piles in the platform level position. On the basis of slope failure in the process and mechanisms qualitative analysis, this paper uses the discrete element program UDEC to carry out the numerical simulation of landslide. Anti-slide piles with prestressed cables can be effective when they are used to against the failure of the slope. In terms of the known sliding plane, the UDEC is used to simulate the excavation and support of the landslide.the comparative analysis of the landslide displacement before and after reinforcement shows that the anti-slide piles with prestressed cable are safe and effective scheme to the landslide. Comparison shows that the anti-slide pile with prestressed anchor cable has many advantages over the anti-slide pile without prestressed anchor cable. For instance, it changes the stress of the traditional anti-slide pile, changes the cantilever beam into the species simply supported beam, and changes the passive support into active support,and so on.
2012, 20(2): 266-275.
This paper was based on the field investigation of the typical geological sections and multiple methods of laboratory tests on the samples from the slopes along the Baoshan-Tengchong highway and adjacent area in Yunnan Province. It discovered a swelling clayey diatomite in the Neogene lacustrine strata, named Mangbang formation, at Tengchong area Yunnan Province. The clayey diatomite is belonging to a type of both light and strong swelling rock, which has double physical-hydraulic properties of both typical diatomite and swelling clay rock. The former include high porosity, high water absorption capacity, and very strong structure, the later include high plasticity, outstanding swelling and disintegration properties, and the appearance of swelling property mainly connected with the contents of organic matter. The discovery of the swelling clayey diatomite in Mangbang Basin, as well as the researches on its engineering properties, is not only instructive for realization of the mechanism of related geo-hazards along the Baoshan-Tengchong high way, but also helpful to understanding the engineering properties of some lacustrine deposits and their easily causing geo-hazards in southwestern China.
This paper was based on the field investigation of the typical geological sections and multiple methods of laboratory tests on the samples from the slopes along the Baoshan-Tengchong highway and adjacent area in Yunnan Province. It discovered a swelling clayey diatomite in the Neogene lacustrine strata, named Mangbang formation, at Tengchong area Yunnan Province. The clayey diatomite is belonging to a type of both light and strong swelling rock, which has double physical-hydraulic properties of both typical diatomite and swelling clay rock. The former include high porosity, high water absorption capacity, and very strong structure, the later include high plasticity, outstanding swelling and disintegration properties, and the appearance of swelling property mainly connected with the contents of organic matter. The discovery of the swelling clayey diatomite in Mangbang Basin, as well as the researches on its engineering properties, is not only instructive for realization of the mechanism of related geo-hazards along the Baoshan-Tengchong high way, but also helpful to understanding the engineering properties of some lacustrine deposits and their easily causing geo-hazards in southwestern China.
2012, 20(2): 276-282.
This paper analyzes the features of deep rock cracks and grouting technology. It then studies the grouting technology with cement-silicate for controlling the deep rock cracks. It particularly addresses the problems of grouting in deep cracks in Jinping Ⅰ Hydropower. First of all, the paper analyzes the mechanism of cement-silicate grouting. Then, it investigates the cement-silicate slurry mainly from the aspects of gel time and strength. It studies the influence law of gel time and strength from the dosage of silicate and retarder. It obtains a design formula for 5min.cement-silicate slurry. Finally, the paper proposes the grouting method using two pipe outlets for mixing the two grout fluids. One pipe outlet is for the cement grout and the other for silicate grout. The grouting method further includes the top-down approach, closed hole, and pure pressure grouting, according to the characteristics of the deep rock cracks. Thus, the paper has initially established the research programs of grouting treatment technology for deep rock cracks at Jinping Ⅰ Hydropower.
This paper analyzes the features of deep rock cracks and grouting technology. It then studies the grouting technology with cement-silicate for controlling the deep rock cracks. It particularly addresses the problems of grouting in deep cracks in Jinping Ⅰ Hydropower. First of all, the paper analyzes the mechanism of cement-silicate grouting. Then, it investigates the cement-silicate slurry mainly from the aspects of gel time and strength. It studies the influence law of gel time and strength from the dosage of silicate and retarder. It obtains a design formula for 5min.cement-silicate slurry. Finally, the paper proposes the grouting method using two pipe outlets for mixing the two grout fluids. One pipe outlet is for the cement grout and the other for silicate grout. The grouting method further includes the top-down approach, closed hole, and pure pressure grouting, according to the characteristics of the deep rock cracks. Thus, the paper has initially established the research programs of grouting treatment technology for deep rock cracks at Jinping Ⅰ Hydropower.
2012, 20(2): 283-288.
With the development of large-scale hydropower projects, large bridges projects, high-rise building projects, and underground space constructions, how to reasonably determine and select the rock mass mechanical parameters is even more important. The results of selection can directly affect the investment and reliability of the engineering projects. At first, this paper briefly introduces the nature and the concept of the quantile regression. Then, It discusses the backgrounds about the studies of the shear strength of well concrete, the shear strength of simulation crack & chemical grouting concrete dam and the shear strength of concrete with some small cracks in a hydropower station. It further examines the requirements of the relevant specifications with dam design. So, the quantile regression is used to the analysis of the selection of the mechanical parameters. At the same time, the paper uses the linear 0.2 sub-bit value method, the point group center method and the priority given slope method to make various analysis results to be compared. It establishes the advantage of the quantile regression for the two-dimensional mechanical parameters of rock mass. Based on the analysis of the content of the above, the quantile regression is first proposed for the selection of the rock mass mechanics parameters, which will serve the construction as a reference to the analysis of parameters.
With the development of large-scale hydropower projects, large bridges projects, high-rise building projects, and underground space constructions, how to reasonably determine and select the rock mass mechanical parameters is even more important. The results of selection can directly affect the investment and reliability of the engineering projects. At first, this paper briefly introduces the nature and the concept of the quantile regression. Then, It discusses the backgrounds about the studies of the shear strength of well concrete, the shear strength of simulation crack & chemical grouting concrete dam and the shear strength of concrete with some small cracks in a hydropower station. It further examines the requirements of the relevant specifications with dam design. So, the quantile regression is used to the analysis of the selection of the mechanical parameters. At the same time, the paper uses the linear 0.2 sub-bit value method, the point group center method and the priority given slope method to make various analysis results to be compared. It establishes the advantage of the quantile regression for the two-dimensional mechanical parameters of rock mass. Based on the analysis of the content of the above, the quantile regression is first proposed for the selection of the rock mass mechanics parameters, which will serve the construction as a reference to the analysis of parameters.
2012, 20(2): 289-295.
This paper is based on a comprehensive literature and a large number experimental tests. It comprehensively analyzes and studies the influences of main factors on strength of soft intercalation. The factors include substance, fabric characteristics, granularity composition, water content and ground stress. They affect the strength parameter of weak intercalation and are mutual restraint and influence, not isolated. Therefore, to take full consideration of all kinds of factors and to catch and hold the main controlling factors are the precondition that the strength parameter of weak intercalation is given correctly and reasonably. Natural characteristic index(w/wP) is a comprehensive index. It reflects the soil water content, degree of density, the types and contents of clay minerals, clay content and consistency conditions. This paper takes Xiangjiaba hydropower construction as an example. It studies the relativity between strength parameter and characteristic index(w/wP). It establishes a functional expression to describe the relation between strength parameter and characteristic index(w/wP). The expression is based on the results obtained from a large number of shear strength tests, water content and liquid/plastic limit determination test. These tests are performed at field or in laboratory. The results show that excellent correlation between strength parameter and characteristic index(w/wP). Therefore, use of relevant equations can conveniently give values of strength parameters of soft/weak intercalation when the natural characteristic index is known.
This paper is based on a comprehensive literature and a large number experimental tests. It comprehensively analyzes and studies the influences of main factors on strength of soft intercalation. The factors include substance, fabric characteristics, granularity composition, water content and ground stress. They affect the strength parameter of weak intercalation and are mutual restraint and influence, not isolated. Therefore, to take full consideration of all kinds of factors and to catch and hold the main controlling factors are the precondition that the strength parameter of weak intercalation is given correctly and reasonably. Natural characteristic index(w/wP) is a comprehensive index. It reflects the soil water content, degree of density, the types and contents of clay minerals, clay content and consistency conditions. This paper takes Xiangjiaba hydropower construction as an example. It studies the relativity between strength parameter and characteristic index(w/wP). It establishes a functional expression to describe the relation between strength parameter and characteristic index(w/wP). The expression is based on the results obtained from a large number of shear strength tests, water content and liquid/plastic limit determination test. These tests are performed at field or in laboratory. The results show that excellent correlation between strength parameter and characteristic index(w/wP). Therefore, use of relevant equations can conveniently give values of strength parameters of soft/weak intercalation when the natural characteristic index is known.
2012, 20(2): 296-303.
The permeability structure of rock mass controls the macro-permeability characteristics of fractured rock mass. However, the geological factors are complex and diverse. They control the permeability structure of rock mass. As to the actual engineering rock mass, the rock permeability structures are the hybrid types that are formed by basic permeable structure types. Through practical research at the field and statistical analysis, this paper summarizes five types of basic permeable structures that are widespread and four types of hybrid permeability structures and percolation characteristics in fractured rock mass. The types are Ⅰ-Ⅱ, Ⅲ-Ⅳ, Ⅰ-Ⅱ-Ⅲ and Ⅰ-Ⅲ-Ⅳ respectively. Using a project instance, this paper analyzes the hybrid permeability structure types of the fractured rock, which are spread in the underground cavern and the switch stations of hydropower stations in southwestern China. At last, it is concluded that based on hybrid permeability structures, the hybrid types of permeable structures are mainly Ⅲ-Ⅳ and Ⅰ-Ⅱ-Ⅲ. Also, the results are more in line with the actual situations.
The permeability structure of rock mass controls the macro-permeability characteristics of fractured rock mass. However, the geological factors are complex and diverse. They control the permeability structure of rock mass. As to the actual engineering rock mass, the rock permeability structures are the hybrid types that are formed by basic permeable structure types. Through practical research at the field and statistical analysis, this paper summarizes five types of basic permeable structures that are widespread and four types of hybrid permeability structures and percolation characteristics in fractured rock mass. The types are Ⅰ-Ⅱ, Ⅲ-Ⅳ, Ⅰ-Ⅱ-Ⅲ and Ⅰ-Ⅲ-Ⅳ respectively. Using a project instance, this paper analyzes the hybrid permeability structure types of the fractured rock, which are spread in the underground cavern and the switch stations of hydropower stations in southwestern China. At last, it is concluded that based on hybrid permeability structures, the hybrid types of permeable structures are mainly Ⅲ-Ⅳ and Ⅰ-Ⅱ-Ⅲ. Also, the results are more in line with the actual situations.
2012, 20(2): 183-188.
This paper aims to study the kinematic features of landslides to assess and mitigate landslide risks. It takes Jiaojiayatou irrigation-induced loess landslide in Heifangtai, Yongjin, Gansu Province as the research object. It is based on engineering geological mapping and soil tests, as well as landslide features analysis. It simulates the whole moving process of the landslide and analyzes the velocity field using the finite-difference-method-based kinematic model. The simulation results show that the velocity field of the landslide can be divided into three stages: the initial acceleration stage, the high-speeding fluctuation stage and the collision deceleration stage. The average velocity in the whole process is about 8.6ms-1,which represents a high-speed moving feature and can cause dangerous results. The velocity at the shear opening from the numerical simulation is 1.2ms-1 higher than that calculated using the ASCE recommended method, 2ms-1 lower than that calculated using the variational method, and close to the lower limit calculated using Pan Jiazheng Method. This study is helpful to the prediction of sliding velocity and influencing area of potential irrigation-induced loess landslides.
This paper aims to study the kinematic features of landslides to assess and mitigate landslide risks. It takes Jiaojiayatou irrigation-induced loess landslide in Heifangtai, Yongjin, Gansu Province as the research object. It is based on engineering geological mapping and soil tests, as well as landslide features analysis. It simulates the whole moving process of the landslide and analyzes the velocity field using the finite-difference-method-based kinematic model. The simulation results show that the velocity field of the landslide can be divided into three stages: the initial acceleration stage, the high-speeding fluctuation stage and the collision deceleration stage. The average velocity in the whole process is about 8.6ms-1,which represents a high-speed moving feature and can cause dangerous results. The velocity at the shear opening from the numerical simulation is 1.2ms-1 higher than that calculated using the ASCE recommended method, 2ms-1 lower than that calculated using the variational method, and close to the lower limit calculated using Pan Jiazheng Method. This study is helpful to the prediction of sliding velocity and influencing area of potential irrigation-induced loess landslides.
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