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Editor Work2012 Vol. 20, No. 1
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The distribution, probability and damage of landslide are three principal factors of the integrative assessment for regional landslide risk. The distribution and influence range of landslides are assessed on the basis of landslide risk zonation, and the probability of landslide is calculated according to the analysis of inducing factors and characteristics of landslides development.; the extent of damage is estimated by the percentage of damage region comparing with study area. The landslide risk integrative assessment model is established by overlaying the three principal factors. This model was applied in the Miyi County, Panzhihua City, Sichuan Province, the risk degree of the study area is lower-middle level which is consistent with the actual situation after the risk assessment.
The distribution, probability and damage of landslide are three principal factors of the integrative assessment for regional landslide risk. The distribution and influence range of landslides are assessed on the basis of landslide risk zonation, and the probability of landslide is calculated according to the analysis of inducing factors and characteristics of landslides development.; the extent of damage is estimated by the percentage of damage region comparing with study area. The landslide risk integrative assessment model is established by overlaying the three principal factors. This model was applied in the Miyi County, Panzhihua City, Sichuan Province, the risk degree of the study area is lower-middle level which is consistent with the actual situation after the risk assessment.
2012, 20(1): 7-14.
The rainstorm induced debris flows have entered a new active period after the Wenchuan Earthquake.Debris flows have huge energy to drain a large amount of sediments and their peak discharges have several times of the normal events.Such results are based on field observation of the rainstorm induced debris flows on 24 September 2008 in the Beichuan epicenter areas.This phenomenon is due to the huge loose materials of earthquake induced landslides in the debris flow watershed.Therefore,it has obvious errors if the existing models are applied to estimate the hazardous zones of debris flows in the epicenter areas.In this way,it needs to establish an appropriate model to predict possible hazardous zones of debris flows in the Wenchuan Earthquake epicenter.This study selects the 9.24 rainstorm induced debris flows as a typical case.It uses the high resolution aerial photograph and SPOT5 images to extract a set of data of landslide volume in debris flow drainage basin and also geometrical dimension of depositional fans.Applying the multivariate regression analysis,a mathematical model is established to estimate the maximum runout distance and depositional width.The validation and application show that the new model is suitable for predicting debris flow hazardous zones in the Wenchuan Earthquake areas.The intent of the study will help future decision makers in the selection of safe sites during the rehabilitation process and also be used as an important basis for landslide risk-management in the rehabilitation area.
The rainstorm induced debris flows have entered a new active period after the Wenchuan Earthquake.Debris flows have huge energy to drain a large amount of sediments and their peak discharges have several times of the normal events.Such results are based on field observation of the rainstorm induced debris flows on 24 September 2008 in the Beichuan epicenter areas.This phenomenon is due to the huge loose materials of earthquake induced landslides in the debris flow watershed.Therefore,it has obvious errors if the existing models are applied to estimate the hazardous zones of debris flows in the epicenter areas.In this way,it needs to establish an appropriate model to predict possible hazardous zones of debris flows in the Wenchuan Earthquake epicenter.This study selects the 9.24 rainstorm induced debris flows as a typical case.It uses the high resolution aerial photograph and SPOT5 images to extract a set of data of landslide volume in debris flow drainage basin and also geometrical dimension of depositional fans.Applying the multivariate regression analysis,a mathematical model is established to estimate the maximum runout distance and depositional width.The validation and application show that the new model is suitable for predicting debris flow hazardous zones in the Wenchuan Earthquake areas.The intent of the study will help future decision makers in the selection of safe sites during the rehabilitation process and also be used as an important basis for landslide risk-management in the rehabilitation area.
2012, 20(1): 15-20.
The mechanism research at present mainly pauses in the qualitative description.The quantitative index is lack in the description of sliding mechanism.Inversion analysis is an important means to determine the strength parameter of sliding zone.Rigid body limit equilibrium method and a global safety factor are used in this paper.So,strength parameter has no direct relation with the sliding mechanism.Three-dimensional stress state and slide direction of the slip layer zone are obtained by numerical computation.Base on the Mohr-Coulomb Strength Criterion,a point safety factor as the ratio of the shear strength of the slip zone to the shear stress parallel to the gliding direction is defined.The safety factor of the landslide as the weighted average value of the zone point safety factor with its zone is defined.The sliding mechanism is studied quantitatively by means of analyzing the distribution of the zone point safety factor.Landslide stability can be evaluated through the safety factor.So a relationship between the sliding mechanism and stability factor is established.In the inversion analysis,the sliding mechanism and stability can be satisfied simultaneously.So the corresponding strength parameter is a reasonable inversion result.This paper uses the example of the large scale geomechanics model test for K49 landslide in Wanliang highway to illustrate the method and procedure for strength parameter inversion of sliding zone based on sliding mechanism analysis.The rationality of this method is shown by the applications.
The mechanism research at present mainly pauses in the qualitative description.The quantitative index is lack in the description of sliding mechanism.Inversion analysis is an important means to determine the strength parameter of sliding zone.Rigid body limit equilibrium method and a global safety factor are used in this paper.So,strength parameter has no direct relation with the sliding mechanism.Three-dimensional stress state and slide direction of the slip layer zone are obtained by numerical computation.Base on the Mohr-Coulomb Strength Criterion,a point safety factor as the ratio of the shear strength of the slip zone to the shear stress parallel to the gliding direction is defined.The safety factor of the landslide as the weighted average value of the zone point safety factor with its zone is defined.The sliding mechanism is studied quantitatively by means of analyzing the distribution of the zone point safety factor.Landslide stability can be evaluated through the safety factor.So a relationship between the sliding mechanism and stability factor is established.In the inversion analysis,the sliding mechanism and stability can be satisfied simultaneously.So the corresponding strength parameter is a reasonable inversion result.This paper uses the example of the large scale geomechanics model test for K49 landslide in Wanliang highway to illustrate the method and procedure for strength parameter inversion of sliding zone based on sliding mechanism analysis.The rationality of this method is shown by the applications.
2012, 20(1): 21-29.
The 5 12 Wenchuan Earthquake induced tens of thousands of landslides.The high landslide induced by the earthquake presents a unique mountain motion and failure model comparing with the landslide induced by gravity.The Miaoba landslide is a typical representative.The Miaoba landslide lies in the middle of the central fault zone of Longmen Mountains.The intensity of the landslide area is Ⅺ.The landslide volume is about 113104m3.Through the field investigation and synthetic analysis,this paper strives to reveal its characteristics and formation mechanism.It takes a detailed partition of the landslide.According to the partition and dynamic characteristics of the landslide,its process can be divided into the following four stages: (a)the embryonic stage; (b)the starting and accelerating stage; (c)the high-speed motion stage; and (d)the stop and accumulation stage.At the embryonic stage,the reasons of the slope rock mass cutting out with high-speed are explained.The reasons are that the earthquake produced the acceleration coupling slope body structures.Its genetic model is the spatial combination of the crack-granular slipping and then the crack-bedding slipping. between the starting and accelerating to the high-speed motion stage,the paper analyzes the movement program of the projectile coupling the landslide topography.The research shows that the landslide from start-up to end only took 32s, and the average speed was about 20.1m s-1.At the stop and accumulation stage,the paper explains the peculiarity of the accumulation(Ⅲ1)area formation coupling trees of the slope and micro-topography.Based on the above analysis of formation mechanism of the landslide,the paper obtains that the functions of coupling dynamic of the internal and external earth are the reasons of forming the high landslide induced by earthquake.
The 5 12 Wenchuan Earthquake induced tens of thousands of landslides.The high landslide induced by the earthquake presents a unique mountain motion and failure model comparing with the landslide induced by gravity.The Miaoba landslide is a typical representative.The Miaoba landslide lies in the middle of the central fault zone of Longmen Mountains.The intensity of the landslide area is Ⅺ.The landslide volume is about 113104m3.Through the field investigation and synthetic analysis,this paper strives to reveal its characteristics and formation mechanism.It takes a detailed partition of the landslide.According to the partition and dynamic characteristics of the landslide,its process can be divided into the following four stages: (a)the embryonic stage; (b)the starting and accelerating stage; (c)the high-speed motion stage; and (d)the stop and accumulation stage.At the embryonic stage,the reasons of the slope rock mass cutting out with high-speed are explained.The reasons are that the earthquake produced the acceleration coupling slope body structures.Its genetic model is the spatial combination of the crack-granular slipping and then the crack-bedding slipping. between the starting and accelerating to the high-speed motion stage,the paper analyzes the movement program of the projectile coupling the landslide topography.The research shows that the landslide from start-up to end only took 32s, and the average speed was about 20.1m s-1.At the stop and accumulation stage,the paper explains the peculiarity of the accumulation(Ⅲ1)area formation coupling trees of the slope and micro-topography.Based on the above analysis of formation mechanism of the landslide,the paper obtains that the functions of coupling dynamic of the internal and external earth are the reasons of forming the high landslide induced by earthquake.
2012, 20(1): 30-36.
The anti-seismic performance of a rock-fill dam is not only determined by its geometry and composition,but also by the intensity of an earthquake to which the dam is subjected.Through critical state sand model cooperating with the concept of state-dependent dilatancy,a group of fully coupled finite element analyses of the response of a central core rock-fill Dam are presented for the study of the seismic performance.The numerical analysis is on the SUMDES2D platform.The dam was built directly on bedrock to earthquakes of different intensities.The dynamic response of the dam under earthquake intensity was analyzed.The calculation results show that,the bigger the earthquake intensity is,the larger the permanent deformation and local deformation would occur in the dam.The analysis provides not only the overall displacement and deformation of the dam,but also the stress path and stress-strain relationship of local soil unit.The inner destructive mechanism of the dam under different seismic intensities is also further discussed.The dynamic response of local soil unit illustrates whether the critical state of the dam is reached based on the site of the unit and its stress state.The soil units near the berm of upstream slope gradually achieve their critical state of the material as the earthquake intensity increases,and have a flow deformation.
The anti-seismic performance of a rock-fill dam is not only determined by its geometry and composition,but also by the intensity of an earthquake to which the dam is subjected.Through critical state sand model cooperating with the concept of state-dependent dilatancy,a group of fully coupled finite element analyses of the response of a central core rock-fill Dam are presented for the study of the seismic performance.The numerical analysis is on the SUMDES2D platform.The dam was built directly on bedrock to earthquakes of different intensities.The dynamic response of the dam under earthquake intensity was analyzed.The calculation results show that,the bigger the earthquake intensity is,the larger the permanent deformation and local deformation would occur in the dam.The analysis provides not only the overall displacement and deformation of the dam,but also the stress path and stress-strain relationship of local soil unit.The inner destructive mechanism of the dam under different seismic intensities is also further discussed.The dynamic response of local soil unit illustrates whether the critical state of the dam is reached based on the site of the unit and its stress state.The soil units near the berm of upstream slope gradually achieve their critical state of the material as the earthquake intensity increases,and have a flow deformation.
2012, 20(1): 37-43.
Slope excavation and rainfall infiltration are often important factors affected slope stability.In this paper,the rebuilding of HuNan national highway is studied.Based on monitoring data and numerical analysis,the process of slope deformation is studied during the slope cutting and under rainfall conditions.The results show that the slope failure is a gradual process.Different factors can influence the slope stability and have different functions in the process.Slope excavation is the inciting factor which can lead to the failure of shallow slope body.For the slope is excavated,the stress balance of the slope body is destroyed.Slope body has a redistributed stress state.Then the shallow sliding surface is formed.The rainfall infiltration is the inciting factor leading to the deep sliding surface.The rainfall infiltrates the slope body along cracks.Deformation difference can increase on the both sides of shallow sliding surface.Then the pull-type landslide can be emerged.The high porewater pressure is in the interface between debris and strong weathered shale.The sliding zone is generated under the action of water-soil gradually.Consequently the deep sliding surface is emerged.
Slope excavation and rainfall infiltration are often important factors affected slope stability.In this paper,the rebuilding of HuNan national highway is studied.Based on monitoring data and numerical analysis,the process of slope deformation is studied during the slope cutting and under rainfall conditions.The results show that the slope failure is a gradual process.Different factors can influence the slope stability and have different functions in the process.Slope excavation is the inciting factor which can lead to the failure of shallow slope body.For the slope is excavated,the stress balance of the slope body is destroyed.Slope body has a redistributed stress state.Then the shallow sliding surface is formed.The rainfall infiltration is the inciting factor leading to the deep sliding surface.The rainfall infiltrates the slope body along cracks.Deformation difference can increase on the both sides of shallow sliding surface.Then the pull-type landslide can be emerged.The high porewater pressure is in the interface between debris and strong weathered shale.The sliding zone is generated under the action of water-soil gradually.Consequently the deep sliding surface is emerged.
2012, 20(1): 44-50.
Slope failure is a major type of geological hazard induced by earthquake.Combining with the engineering project,a numerical simulation model of soil slope is established with the FLAC3D program.The paper examines and compares the plastic zone,horizontal displacement and the fracture surface of slope whether supported with bolts or not under static state, and the axial force of bolts,the plastic zone,horizontal displacement and plastic state of slope whether supported with bolts or not under stability of the slope with and without bolts at different time under static state and earthquake.It distinguishes the stability of slopes and discusses the failure mechanism of slopes.It is shown that,the bolts for slope have very good supporting role.Bolts in supporting role plays the role mainly by pulling force, and along with the increase of elevation and the decreases of axial force.Slope with or without bolts under earthquake can be damaged in different ways.Research results can be the reference frame for the design of slopes supported with bolts under earthquake.
Slope failure is a major type of geological hazard induced by earthquake.Combining with the engineering project,a numerical simulation model of soil slope is established with the FLAC3D program.The paper examines and compares the plastic zone,horizontal displacement and the fracture surface of slope whether supported with bolts or not under static state, and the axial force of bolts,the plastic zone,horizontal displacement and plastic state of slope whether supported with bolts or not under stability of the slope with and without bolts at different time under static state and earthquake.It distinguishes the stability of slopes and discusses the failure mechanism of slopes.It is shown that,the bolts for slope have very good supporting role.Bolts in supporting role plays the role mainly by pulling force, and along with the increase of elevation and the decreases of axial force.Slope with or without bolts under earthquake can be damaged in different ways.Research results can be the reference frame for the design of slopes supported with bolts under earthquake.
2012, 20(1): 51-57.
The maximum entropy method is used to conduct the reliability analysis for slope engineering.The entropy is enlarged by the partial information of the existed samples.The high order moment information of the random variables fully uses the sample moment to infer the slope reliability probability density function.Then the slope failure probability is calculated.This method is for the distribution of basic random variables without special requirement.It avoids the conventional method in the process of computation in the iteration points for non-normal random variables to approximate the yield of the normal processes defects.Usually,the function of real probability density function is difficult to obtain,even cant be calculated.So the Pearson curve clan is introduced to solve the high-order moment for geotechnical parameter random variable.It can easily get the function of high order center.It is based on the maximum entropy principle moment fitting get function of maximum entropy density function.It uses the interval truncation method and Gauss-Kronrod respectively to determine the maximum entropy density function.An example is analyzed.The results show that this method is of high efficiency,reliable.It overcomes the problem of the traditional methods that the solving process is complicated and low accuracy of faults.The new method is applied in the reliability analysis of slope engineering.It has certain application prospect and practical value.
The maximum entropy method is used to conduct the reliability analysis for slope engineering.The entropy is enlarged by the partial information of the existed samples.The high order moment information of the random variables fully uses the sample moment to infer the slope reliability probability density function.Then the slope failure probability is calculated.This method is for the distribution of basic random variables without special requirement.It avoids the conventional method in the process of computation in the iteration points for non-normal random variables to approximate the yield of the normal processes defects.Usually,the function of real probability density function is difficult to obtain,even cant be calculated.So the Pearson curve clan is introduced to solve the high-order moment for geotechnical parameter random variable.It can easily get the function of high order center.It is based on the maximum entropy principle moment fitting get function of maximum entropy density function.It uses the interval truncation method and Gauss-Kronrod respectively to determine the maximum entropy density function.An example is analyzed.The results show that this method is of high efficiency,reliable.It overcomes the problem of the traditional methods that the solving process is complicated and low accuracy of faults.The new method is applied in the reliability analysis of slope engineering.It has certain application prospect and practical value.
2012, 20(1): 58-65.
For better understanding the change behavior of temperature in urban and rural shallow soils,two long-term observation stations were built and a large amount of measurement points were also selected in urban and rural areas of Nanjing city.By analyzing the obtained soil temperature data,it is found that the average annual temperature of urban soil is 19.23℃.It is 2.02℃ higher than that of the rural soil.Such result reveals an obvious dry island effect in the urban soil.The soil temperature differences between urban and rural areas show evident temporal-spatial characteristics.In temporal pattern,the average daily temperature difference between urban and rural soils ranges from 0.37 to 3.83℃, and shows significant variability over short time scales.The average monthly difference ranges from 1.34 to 2.9℃.The minimum and maximum monthly differences occur in November and July respectively.The average seasonal difference ranges from 1.53 to 2.45℃.The minimum and maximum seasonal differences occur in summer and autumn respectively.In spatial pattern,the critical affected depth of daily synoptic events on soil temperature is approximately 60cm.Below this critical depth,there is a time delay to the effects of synoptic events.An evident hysteresis(about one month delay per 100cm depth increment)can be observed.Within the 0～300cm depth,the temperature difference between urban and rural soil generally increases as the depth increases.In addition,it is found that the soil temperature in urban area is much more variable than that observed in rural area.
For better understanding the change behavior of temperature in urban and rural shallow soils,two long-term observation stations were built and a large amount of measurement points were also selected in urban and rural areas of Nanjing city.By analyzing the obtained soil temperature data,it is found that the average annual temperature of urban soil is 19.23℃.It is 2.02℃ higher than that of the rural soil.Such result reveals an obvious dry island effect in the urban soil.The soil temperature differences between urban and rural areas show evident temporal-spatial characteristics.In temporal pattern,the average daily temperature difference between urban and rural soils ranges from 0.37 to 3.83℃, and shows significant variability over short time scales.The average monthly difference ranges from 1.34 to 2.9℃.The minimum and maximum monthly differences occur in November and July respectively.The average seasonal difference ranges from 1.53 to 2.45℃.The minimum and maximum seasonal differences occur in summer and autumn respectively.In spatial pattern,the critical affected depth of daily synoptic events on soil temperature is approximately 60cm.Below this critical depth,there is a time delay to the effects of synoptic events.An evident hysteresis(about one month delay per 100cm depth increment)can be observed.Within the 0～300cm depth,the temperature difference between urban and rural soil generally increases as the depth increases.In addition,it is found that the soil temperature in urban area is much more variable than that observed in rural area.
2012, 20(1): 66-73.
As a large number of deep and long tunnel is being constructed,the geostress effects and especially the high geostress effects to surrounding rock classification becomes more and more challenging. at present,the common surrounding rock classification method is to select a few indicators,then to assign some values,then to make relevant classifications.Some surrounding rock classification method cannot flexibly choose the rock classification geological indexes.Some classification indexes can influence each other.The surrounding rock classification is a complicated problem of conflicting.The extension theory methods can be used to translate the conflicting problem into the exclusive problem.This method is worthy for exploration and use.This paper combines the extension theory methods with the surrounding rock classification for high geostress tunnel.It establishes the method of rock classification for high geostress tunnel based on extension theory.The method mainly t selects the important parameters of rock classification indices that can reflect and embody the featureuniaxial compressive strength Rc,RQD index,the index Kv of rockmass integrity,index of groundwater state.It especially considers the important index with geostress.It then bases on matter-element theory,extension set and dependent function calculation to establish the material element model of the surrounding rock classification.It follows the degree of association calculations for the actual rock classification.The final rock classification can determined.the paper applies the method to actual cases.
As a large number of deep and long tunnel is being constructed,the geostress effects and especially the high geostress effects to surrounding rock classification becomes more and more challenging. at present,the common surrounding rock classification method is to select a few indicators,then to assign some values,then to make relevant classifications.Some surrounding rock classification method cannot flexibly choose the rock classification geological indexes.Some classification indexes can influence each other.The surrounding rock classification is a complicated problem of conflicting.The extension theory methods can be used to translate the conflicting problem into the exclusive problem.This method is worthy for exploration and use.This paper combines the extension theory methods with the surrounding rock classification for high geostress tunnel.It establishes the method of rock classification for high geostress tunnel based on extension theory.The method mainly t selects the important parameters of rock classification indices that can reflect and embody the featureuniaxial compressive strength Rc,RQD index,the index Kv of rockmass integrity,index of groundwater state.It especially considers the important index with geostress.It then bases on matter-element theory,extension set and dependent function calculation to establish the material element model of the surrounding rock classification.It follows the degree of association calculations for the actual rock classification.The final rock classification can determined.the paper applies the method to actual cases.
2012, 20(1): 74-81.
This paper examines the the holistic heterotopia and fluctuation phenomena of the sonic wave curves. The curves are obtained through sonic contrastive tests in single bore. Some contrasts are made among the curves integrated with the actually sonic test data. On the basis of contrasts, concrete manifestation and characteristic feature of the abnormity are presented. Then the mainly reason for this abnormity is analyzed. The result demonstrates that the sonic test abnormity is mainly caused by substandard test operation. In particular, the holistic heterotopia associated with the sonic wave curves was caused by the erroneous sampling. It belongs to linear systematic error, and can be dealt with increasing the length of contrast rockmass units, which is in order to increase the overlap ration of sampling mass. But the holistic uneven fluctuation in the sonic wave curves is mainly related to the purity of the water that was used as the coupling reagent in sonic test. It belongs to nonlinear systematic error. So this abnormity is difficult to be remedied. This study offers some references to avoid or remove the abnormity occurring in the contrast sonic test.
This paper examines the the holistic heterotopia and fluctuation phenomena of the sonic wave curves. The curves are obtained through sonic contrastive tests in single bore. Some contrasts are made among the curves integrated with the actually sonic test data. On the basis of contrasts, concrete manifestation and characteristic feature of the abnormity are presented. Then the mainly reason for this abnormity is analyzed. The result demonstrates that the sonic test abnormity is mainly caused by substandard test operation. In particular, the holistic heterotopia associated with the sonic wave curves was caused by the erroneous sampling. It belongs to linear systematic error, and can be dealt with increasing the length of contrast rockmass units, which is in order to increase the overlap ration of sampling mass. But the holistic uneven fluctuation in the sonic wave curves is mainly related to the purity of the water that was used as the coupling reagent in sonic test. It belongs to nonlinear systematic error. So this abnormity is difficult to be remedied. This study offers some references to avoid or remove the abnormity occurring in the contrast sonic test.
2012, 20(1): 82-87.
The clay with low permeability in aquitard or/ and interbedded layer is the substance base of subsidence in the Huabei Plain,China.The seepage flow characteristics in clay can greatly impact the evaluation,simulation and prediction of the land subsidence.In this paper,soil samples are taken from the subsidence center at Hengshui and tested in laboratory.First,seepage tests are carried out by the high confining pressure triaxial seepage equipment.The test results indicate that the permeability of clay changes with the soil depth and the applied seepage pressure.The greater the soil depth and the seepage pressure are,the smaller the permeability is.Temporally,the permeability of the clay decreases rapidly at the beginning of the test.Then it stabilizes gradually.But due to the seasonally groundwater level fluctuations or excessive groundwater pumpage,the permeability values of some clay soil samples show different patterns.Finally,electron microscope scanning and fractal technology are used to analyze the control effect of microstructure of clay on the seepage flow characteristics.
The clay with low permeability in aquitard or/ and interbedded layer is the substance base of subsidence in the Huabei Plain,China.The seepage flow characteristics in clay can greatly impact the evaluation,simulation and prediction of the land subsidence.In this paper,soil samples are taken from the subsidence center at Hengshui and tested in laboratory.First,seepage tests are carried out by the high confining pressure triaxial seepage equipment.The test results indicate that the permeability of clay changes with the soil depth and the applied seepage pressure.The greater the soil depth and the seepage pressure are,the smaller the permeability is.Temporally,the permeability of the clay decreases rapidly at the beginning of the test.Then it stabilizes gradually.But due to the seasonally groundwater level fluctuations or excessive groundwater pumpage,the permeability values of some clay soil samples show different patterns.Finally,electron microscope scanning and fractal technology are used to analyze the control effect of microstructure of clay on the seepage flow characteristics.
2012, 20(1): 88-95.
The results of studies on the deformation and mechanical properties of rock at intermediate strain rates at home and abroad are summarized in this paper.The development of intermediate strain rate test instruments,compression and tensile tests at intermediate strain rates,failure mechanisms of rock materials at intermediate strain rates and numerical simulation are further discussed in detail.The drawbacks and unresolved problems in the relevant studies are summed up.Finally,several key issues are needed to be solved in further studies.
The results of studies on the deformation and mechanical properties of rock at intermediate strain rates at home and abroad are summarized in this paper.The development of intermediate strain rate test instruments,compression and tensile tests at intermediate strain rates,failure mechanisms of rock materials at intermediate strain rates and numerical simulation are further discussed in detail.The drawbacks and unresolved problems in the relevant studies are summed up.Finally,several key issues are needed to be solved in further studies.
EXPERIMENTAL AND NUMERICAL ANALYSIS ON THE ARCHING ACTION FROM STRESS ADJUSTING IN SURROUNDING ROCKS
2012, 20(1): 96-102.
In this paper,after the stress analysis of surrounding rocks,excavation simulated experiments and numerical calculation are applied to study the characteristics of arching action under conditions of different rock properties.Firstly,inner boundary and thickness are used to define an arch in surrounding rocks and to evaluate the stability of underground openings.When the inner boundary is near openings,the surrounding rocks are stable.The thickness of arching action indicates the extent to which the surrounding rocks are influenced by excavation.Less thickness means fewer rocks are used to sustain their own weight and that of rocks above.Then,the arching action is defined in the excavation simulated experiment.In this experiment,it is observed and analyzed that the increase of tangential stresses occurs and an arch is formed around an opening.Data from the experiment show that the increase of displacements is greater near the opening.In numerical analysis,it is found that joints have great influence on the formation of an arch.The position of inner boundary of pressure arch is far away from an opening and thickness is greater with the decrease of joint space.And,in rock mass containing two sets of joint,when a joint incline angle is 30 degree or 60 degree respectively,it is disadvantageous for an arch formation.In addition,the influence degree of joint cohesion on arching action is related to joint friction angle.When the joint friction angle is more than 20 degree,the joint cohesion influence is negligible.
In this paper,after the stress analysis of surrounding rocks,excavation simulated experiments and numerical calculation are applied to study the characteristics of arching action under conditions of different rock properties.Firstly,inner boundary and thickness are used to define an arch in surrounding rocks and to evaluate the stability of underground openings.When the inner boundary is near openings,the surrounding rocks are stable.The thickness of arching action indicates the extent to which the surrounding rocks are influenced by excavation.Less thickness means fewer rocks are used to sustain their own weight and that of rocks above.Then,the arching action is defined in the excavation simulated experiment.In this experiment,it is observed and analyzed that the increase of tangential stresses occurs and an arch is formed around an opening.Data from the experiment show that the increase of displacements is greater near the opening.In numerical analysis,it is found that joints have great influence on the formation of an arch.The position of inner boundary of pressure arch is far away from an opening and thickness is greater with the decrease of joint space.And,in rock mass containing two sets of joint,when a joint incline angle is 30 degree or 60 degree respectively,it is disadvantageous for an arch formation.In addition,the influence degree of joint cohesion on arching action is related to joint friction angle.When the joint friction angle is more than 20 degree,the joint cohesion influence is negligible.
2012, 20(1): 103-108.
This paper is to find out the strain property,distribution and its variation of the saturated expansive soil during its shrinking and cracking process under the condition of dehydration.A one-dimensional model tank of 40cm long, 5cm wide and 3cm high was designed and used for the purpose.The tank was filled with the saturated expansive soil and three grating sensing fibers with 11 FBG sensors were buried into the soil to measure the strain at different positions.Based on the measured strains and their variation,the paper obtained the characteristics of soil stain distribution and its temporal-spatial evolution process,especially the strain distribution on and around the first fissures.It was found that,the soil shows global shrinkage initially with the reduction of soil moisture content.Afterwards,differentiation of the soil stains occurred,showing alternate distribution of tension and compression.At the edge of the maximal shrinking area,when the state of FBG sensors was changed from compression to tension,the first fissure would appear in the region of higher tensile strain and strain variation rate.Thus,the FBG sensing technology of high spatial resolution can be a new idea and technology used for the analysis of the whole shrinking and cracking process of the expansive soil,revealing the cracking mechanism of expansive soil during the dehydration.
This paper is to find out the strain property,distribution and its variation of the saturated expansive soil during its shrinking and cracking process under the condition of dehydration.A one-dimensional model tank of 40cm long, 5cm wide and 3cm high was designed and used for the purpose.The tank was filled with the saturated expansive soil and three grating sensing fibers with 11 FBG sensors were buried into the soil to measure the strain at different positions.Based on the measured strains and their variation,the paper obtained the characteristics of soil stain distribution and its temporal-spatial evolution process,especially the strain distribution on and around the first fissures.It was found that,the soil shows global shrinkage initially with the reduction of soil moisture content.Afterwards,differentiation of the soil stains occurred,showing alternate distribution of tension and compression.At the edge of the maximal shrinking area,when the state of FBG sensors was changed from compression to tension,the first fissure would appear in the region of higher tensile strain and strain variation rate.Thus,the FBG sensing technology of high spatial resolution can be a new idea and technology used for the analysis of the whole shrinking and cracking process of the expansive soil,revealing the cracking mechanism of expansive soil during the dehydration.
2012, 20(1): 109-115.
The paper proposes a new method of reinforcing deep and thick silt.The method uses the short-range and over-loading vacuum preloading dynamic drainage consolidation approach.It is based on the conclusion of soft soil drainage consolidation of S-T roundabout regularities.It is developed according to the characteristics of deep and thick silt soft soil in coastal areas and the requirements of engineering constructions substantial results.The approach also demonstrates that the primary consolidation settlement of deep and thick silt soft soil can be accomplished in a short time,under the optional regrouping of vacuum negative pressure and over-loading positive pressure as well as dynamic impact.The silt soft soil consolidation and settlement are capable of improving the intensity of the solid body while the ground surface dredged fill can become over-consolidating hard shell course under the dynamic impact.The consolidation of deep and thick silt soft soil can meet the requirements of ground bearing capacity and effectively control past-construction settlement and uneven settlement.The case study and the analysis as well as the assessment of the effect of groundwork dealings show the feasibility and validity of this new method.It provides a new way of reinforcing deep and thick silt soft soil groundwork widely spread in coastal areas.
The paper proposes a new method of reinforcing deep and thick silt.The method uses the short-range and over-loading vacuum preloading dynamic drainage consolidation approach.It is based on the conclusion of soft soil drainage consolidation of S-T roundabout regularities.It is developed according to the characteristics of deep and thick silt soft soil in coastal areas and the requirements of engineering constructions substantial results.The approach also demonstrates that the primary consolidation settlement of deep and thick silt soft soil can be accomplished in a short time,under the optional regrouping of vacuum negative pressure and over-loading positive pressure as well as dynamic impact.The silt soft soil consolidation and settlement are capable of improving the intensity of the solid body while the ground surface dredged fill can become over-consolidating hard shell course under the dynamic impact.The consolidation of deep and thick silt soft soil can meet the requirements of ground bearing capacity and effectively control past-construction settlement and uneven settlement.The case study and the analysis as well as the assessment of the effect of groundwork dealings show the feasibility and validity of this new method.It provides a new way of reinforcing deep and thick silt soft soil groundwork widely spread in coastal areas.
2012, 20(1): 116-122.
This paper is based all kinds of soft soil foundation monitoring results of a first-class highway.The monitoring data of the foundation surface settlement,porewater pressure,soil horizontal displacement variation rules of time and space are analyzed in detail.The results show that about 65 percents of the total settlement of foundation is due to the silt layer.The horizontal displacement of low liquid limit clay layer(under 15m) is smaller.It is related to its bigger soil intensity.Excessive fast filling velocity can make the general excessive porewater pressure above zero.Therefore close observation of the data of pore pressure is needed in surcharge preloading process in order to prevent the foundation instability.There is nearly no surface horizontal displacement at more than 30m outside the reinforced area,which has no effect on river embankment security.Combined with the monitoring data of porepressure and layered settlement,the effective influence depth of the foundation by vacuum combined surcharge preloading can reach to about 2m.
This paper is based all kinds of soft soil foundation monitoring results of a first-class highway.The monitoring data of the foundation surface settlement,porewater pressure,soil horizontal displacement variation rules of time and space are analyzed in detail.The results show that about 65 percents of the total settlement of foundation is due to the silt layer.The horizontal displacement of low liquid limit clay layer(under 15m) is smaller.It is related to its bigger soil intensity.Excessive fast filling velocity can make the general excessive porewater pressure above zero.Therefore close observation of the data of pore pressure is needed in surcharge preloading process in order to prevent the foundation instability.There is nearly no surface horizontal displacement at more than 30m outside the reinforced area,which has no effect on river embankment security.Combined with the monitoring data of porepressure and layered settlement,the effective influence depth of the foundation by vacuum combined surcharge preloading can reach to about 2m.
2012, 20(1): 123-130.
Slopes in hydropower engineering are more complicated,higher and steeper than other engineering slopes.Due to the complex geological conditions and large scale man-made activities,the stability of the high slopes has become one of the key problems.A reasonable slope classification system is not only helpful for the description and stability analysis of slopes,but also useful for the geological investigation,design and construction of hydropower projects.Based on the insight of slope classifications in the world and the authors practice experience,the existing specification of slope classification is needed to be modified.A new classification systemic frame is put forwarded in this paper.It takes the hydropower project relationship into consideration and combines the existing schematic achievements.According to the relationship with the project site,the slopes are firstly classified into 2 categories, i.e., dam area slopes and reservoir area slopes.The dam area slopes are further classified into cut slopes and surrounding slopes.Then,slopes are classified 5 ranks according to the importance of hydropower project and the hazards of slopes.Thirdly,it is classified according to characteristics of slope,geometric dimensions of slope,deformation or failure models.Finally,slopes are further classified into different types depending on the lithology,slope structure,inclination angle of slopes,height of slopes,deformation mechanism,failure mode and hazard resources.It is suggested that very steep slopes and hang slopes are divided by 60of inclination angle.High slopes and extra high slopes are divided by 80m of slope heights.The surrounding slopes are classified by the hazard resources.It is found that to use slope mass structure for slope classification is better than to use rock mass structure because slope mass structure is related with the slope stability.
Slopes in hydropower engineering are more complicated,higher and steeper than other engineering slopes.Due to the complex geological conditions and large scale man-made activities,the stability of the high slopes has become one of the key problems.A reasonable slope classification system is not only helpful for the description and stability analysis of slopes,but also useful for the geological investigation,design and construction of hydropower projects.Based on the insight of slope classifications in the world and the authors practice experience,the existing specification of slope classification is needed to be modified.A new classification systemic frame is put forwarded in this paper.It takes the hydropower project relationship into consideration and combines the existing schematic achievements.According to the relationship with the project site,the slopes are firstly classified into 2 categories, i.e., dam area slopes and reservoir area slopes.The dam area slopes are further classified into cut slopes and surrounding slopes.Then,slopes are classified 5 ranks according to the importance of hydropower project and the hazards of slopes.Thirdly,it is classified according to characteristics of slope,geometric dimensions of slope,deformation or failure models.Finally,slopes are further classified into different types depending on the lithology,slope structure,inclination angle of slopes,height of slopes,deformation mechanism,failure mode and hazard resources.It is suggested that very steep slopes and hang slopes are divided by 60of inclination angle.High slopes and extra high slopes are divided by 80m of slope heights.The surrounding slopes are classified by the hazard resources.It is found that to use slope mass structure for slope classification is better than to use rock mass structure because slope mass structure is related with the slope stability.
2012, 20(1): 131-137.
At present,the calculation theories for soft soil subgrade are not still perfect.The subgrade of the first runway in PUDONG AIRPORT is built on a typical soft soil area in Shanghai.Its pavement settlement has been measured for 11 years.This paper analyzes the measured pavement settlement data and finds the rules of runway subgrade settlement.The foundation settlement model is also put up.The subgrade settlement of the first runway is mainly induced by static loading.Meanwhile,the moving aircraft loading and groundwater withdraw cannot be ignored also.The calculation method and the rules of settlement induced by moving aircraft loading are put forward.The most of the subgrade settlement induced by moving aircraft loading is produced in the two or three years after the runway was commissioned.Compared with the moving aircraft loading,the groundwater withdraw can produce more subgrade settlement.In different time,the subgrade settlement constitutes differently.By the April of 2009,the subgrade settlement of the first runway was about 54cm.About 33cm of the settlementwas induced by static loading, 5cm was induced by the moving aircraft loading,and 16cm was induced by groundwater withdraw.
At present,the calculation theories for soft soil subgrade are not still perfect.The subgrade of the first runway in PUDONG AIRPORT is built on a typical soft soil area in Shanghai.Its pavement settlement has been measured for 11 years.This paper analyzes the measured pavement settlement data and finds the rules of runway subgrade settlement.The foundation settlement model is also put up.The subgrade settlement of the first runway is mainly induced by static loading.Meanwhile,the moving aircraft loading and groundwater withdraw cannot be ignored also.The calculation method and the rules of settlement induced by moving aircraft loading are put forward.The most of the subgrade settlement induced by moving aircraft loading is produced in the two or three years after the runway was commissioned.Compared with the moving aircraft loading,the groundwater withdraw can produce more subgrade settlement.In different time,the subgrade settlement constitutes differently.By the April of 2009,the subgrade settlement of the first runway was about 54cm.About 33cm of the settlementwas induced by static loading, 5cm was induced by the moving aircraft loading,and 16cm was induced by groundwater withdraw.
2012, 20(1): 138-143.
High strain dynamic testing method has been more widely used now.It is important to study the reliability of test results for projects.In this paper,the ultimate bearing capacity of single PHC pile is determined by static loading test and high strain test.There are two different diameters of the six test piles.At first,the six piles are tested with the high strain method.The results are obtained with the GOBLE-CAPWAPC-CASE method.Then the piles are tested with the static vertical load testing and slow maintenance loading method.Comparing the results of the two methods,the bearing capacity of the piles by the high strain dynamic testing method is higher than that of the piles tested by the static loading test.The differences are relative with the testing principles,calculating methods and different affecting factors of the two methods.The idealized pile-soil system and how to set the main parameters of high strain method have great influence on the results.How to use the values should be fully considered in testing.
High strain dynamic testing method has been more widely used now.It is important to study the reliability of test results for projects.In this paper,the ultimate bearing capacity of single PHC pile is determined by static loading test and high strain test.There are two different diameters of the six test piles.At first,the six piles are tested with the high strain method.The results are obtained with the GOBLE-CAPWAPC-CASE method.Then the piles are tested with the static vertical load testing and slow maintenance loading method.Comparing the results of the two methods,the bearing capacity of the piles by the high strain dynamic testing method is higher than that of the piles tested by the static loading test.The differences are relative with the testing principles,calculating methods and different affecting factors of the two methods.The idealized pile-soil system and how to set the main parameters of high strain method have great influence on the results.How to use the values should be fully considered in testing.
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