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Editor Work2006 Vol. 14, No. 2
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2006, 14(2): 145-151.
Abstract
The debris flows have a wide distribution and frequent occurrence in the reservoir of a hydropower station,which is located in the Meigu River of Jinshajiang.The survey results show there are 31 debris flow valleys of different types in the reservoir area.Among them,4 valleys are classified as at a high hazard level,and 15 are at a moderate hazard level.The results indicate the debris flow activities in the study area will not result in blocking of the main channel that possibly brings about flood in the downstream of the river.However,debris flow hazards have a great potential impact on the hydropower station during the engineering construction.Debris flow valleys near the dam pose a great potential threat to the dam safety.After inundation of the reservoir,most debris flow hazards will be reduced to an acceptable level,but debris flows in the lower reaches near the dam still have influence on operation of the hydropower station.
The debris flows have a wide distribution and frequent occurrence in the reservoir of a hydropower station,which is located in the Meigu River of Jinshajiang.The survey results show there are 31 debris flow valleys of different types in the reservoir area.Among them,4 valleys are classified as at a high hazard level,and 15 are at a moderate hazard level.The results indicate the debris flow activities in the study area will not result in blocking of the main channel that possibly brings about flood in the downstream of the river.However,debris flow hazards have a great potential impact on the hydropower station during the engineering construction.Debris flow valleys near the dam pose a great potential threat to the dam safety.After inundation of the reservoir,most debris flow hazards will be reduced to an acceptable level,but debris flows in the lower reaches near the dam still have influence on operation of the hydropower station.
2006, 14(2): 152-158.
Studies on the 6.1 debris flows in Meigu county of Liangshan state,Sichuan show that the return periods of the debris flows are approximately 20 years and are small/moderate magenitude debris flows.The rainstorm and hail with short duration and high density in the upper reaches of the drainage basins are the triggering factors for the debris flows.The degenerate ecological environment in the drainage basin,unstable slopes in the low-middle reaches and a lot of unconsolidated materials in the channels of the gullies,provide enough materials for the debris flows.The debris flows are typically of the grain curve characteristics with multiple peaks.The deposits of the debris flows have a high content of clay.The large boulders,the boulder piling up boulder,mud crack,lateral accumulation mound and surge deposits demonstrate the debris flows are viscous.Hazardousness assessment indicates,the Caimoluo gully is a high hazardous debris flow gully and has the hazard degree of 0.67;the Naituo gully is a moderate hazardous debris flow gully and has the hazard degree of 0.58.Risk assessment implies the two gullies have high debris flow risk,respectively with the risk degree of 0.52 and 0.45.The debris flows occurred in the high risky area resulted in huge losses of property and life.
Studies on the 6.1 debris flows in Meigu county of Liangshan state,Sichuan show that the return periods of the debris flows are approximately 20 years and are small/moderate magenitude debris flows.The rainstorm and hail with short duration and high density in the upper reaches of the drainage basins are the triggering factors for the debris flows.The degenerate ecological environment in the drainage basin,unstable slopes in the low-middle reaches and a lot of unconsolidated materials in the channels of the gullies,provide enough materials for the debris flows.The debris flows are typically of the grain curve characteristics with multiple peaks.The deposits of the debris flows have a high content of clay.The large boulders,the boulder piling up boulder,mud crack,lateral accumulation mound and surge deposits demonstrate the debris flows are viscous.Hazardousness assessment indicates,the Caimoluo gully is a high hazardous debris flow gully and has the hazard degree of 0.67;the Naituo gully is a moderate hazardous debris flow gully and has the hazard degree of 0.58.Risk assessment implies the two gullies have high debris flow risk,respectively with the risk degree of 0.52 and 0.45.The debris flows occurred in the high risky area resulted in huge losses of property and life.
2006, 14(2): 159-164.
The Danba Sopo deposits,a huge Quaternary accumulation of soils and rock blocks,are distributed in the banks of Dadu River near Houziyan hydropower dam.There are 144 Stone Towers made by ancient Tibetan scattered on this deposit.The formation of the huge deposits were considered as glaciation,glacio-fluvium or debris-flow.The paper presents a detailed field investigation of the deposits.The formation of the huge deposits is further examined. It is found that the deposits at left bank are formed mainly through collapsing and sliding of mountainous slopes and the deposits at the right bank are a accumulation of slope collapses mixed with glacio-fluvial and debris-flow deposits.The findings are validated!with drillhole exploration in the deposits.The findings may be valuable to the understanding of the formation of thick deposits at the western Sichuan region and to the protection measures of the Stone Towers.
The Danba Sopo deposits,a huge Quaternary accumulation of soils and rock blocks,are distributed in the banks of Dadu River near Houziyan hydropower dam.There are 144 Stone Towers made by ancient Tibetan scattered on this deposit.The formation of the huge deposits were considered as glaciation,glacio-fluvium or debris-flow.The paper presents a detailed field investigation of the deposits.The formation of the huge deposits is further examined. It is found that the deposits at left bank are formed mainly through collapsing and sliding of mountainous slopes and the deposits at the right bank are a accumulation of slope collapses mixed with glacio-fluvial and debris-flow deposits.The findings are validated!with drillhole exploration in the deposits.The findings may be valuable to the understanding of the formation of thick deposits at the western Sichuan region and to the protection measures of the Stone Towers.
2006, 14(2): 165-171.
Toppling failure is one of deformation and failure types of bedded rock mass with high dip angle.It usually develops near the ground surface.It is thought that only small-scale toppling deformation can be retained completely before.Owing to the special topographic feature and structure of rock mass,a large-scale intact toppling deformation body was found at present at Xiaowan Hydropower Station left bank slope front dam.The toppling deformation body is near to the damsite and shows higher terrain.Once the toppling deformation failures happen the loss will be disastrous for the construction of the Hydropower Station.The size and structure of the rock mass was found out so as to offer evidences for choice of support projects and evaluation of the slope stability.Based on the field investigation,we discovered that a large-scale toppling deformation occurred at the damsite,which was developed to a great depth of about 200m.In this paper,the deformation phenomena revealed by surface excavation and underground galleries were described in detail including variation of the dip angle and rock mass structure.In terms of these,a mechanical model of the slope deformation is established and its formation process is analyzed.
Toppling failure is one of deformation and failure types of bedded rock mass with high dip angle.It usually develops near the ground surface.It is thought that only small-scale toppling deformation can be retained completely before.Owing to the special topographic feature and structure of rock mass,a large-scale intact toppling deformation body was found at present at Xiaowan Hydropower Station left bank slope front dam.The toppling deformation body is near to the damsite and shows higher terrain.Once the toppling deformation failures happen the loss will be disastrous for the construction of the Hydropower Station.The size and structure of the rock mass was found out so as to offer evidences for choice of support projects and evaluation of the slope stability.Based on the field investigation,we discovered that a large-scale toppling deformation occurred at the damsite,which was developed to a great depth of about 200m.In this paper,the deformation phenomena revealed by surface excavation and underground galleries were described in detail including variation of the dip angle and rock mass structure.In terms of these,a mechanical model of the slope deformation is established and its formation process is analyzed.
2006, 14(2): 172-177.
The geological investigation at the Three Gorges Reservoir has shown that the bank slope-collapses under different riverbank structures have substantial differences.Based on the field investigation and analysis,the typical bank slope collapsess can be classified into the following five types:(a) washing and abrasion type,(b) soil collapse type including wave washing step type,backward collapsing type and cave collapsing type,(c) rock sliding type including rock block sliding type,up hard-down soft type and down concave type,(d) slope type including renew ancient slide,deep talus only superficial soil sliding type,along bedrock-cover sliding type and bedding sliding type, and(e) flowing soil type.Based on the classification,the further examination are presented.They include the evolutionary processes,,development and distribution characteristics,and relationship with soil structures,landform,and geomorphy.Finally the general geological conditions for forming typical bank slope-collapses are summarized.
The geological investigation at the Three Gorges Reservoir has shown that the bank slope-collapses under different riverbank structures have substantial differences.Based on the field investigation and analysis,the typical bank slope collapsess can be classified into the following five types:(a) washing and abrasion type,(b) soil collapse type including wave washing step type,backward collapsing type and cave collapsing type,(c) rock sliding type including rock block sliding type,up hard-down soft type and down concave type,(d) slope type including renew ancient slide,deep talus only superficial soil sliding type,along bedrock-cover sliding type and bedding sliding type, and(e) flowing soil type.Based on the classification,the further examination are presented.They include the evolutionary processes,,development and distribution characteristics,and relationship with soil structures,landform,and geomorphy.Finally the general geological conditions for forming typical bank slope-collapses are summarized.
2006, 14(2): 178-183.
Earth fissures are a serious geological hazard in Hebei Plain.This paper presents their temporal and spatial variations.The majority of earth fissures occur in alluvial-proluvial apron zone.Earth fissures express themselves at land surface as straight line,crenata,polygonal line and forniciform.The spatial distribution of ground fissures can be characterized as directional,cluster and systematic.Length and intensity of earth fissures also vary with time.The primary causes for earth fissuring includes earthquake activities,groundwater overdraft and ground collapse.
Earth fissures are a serious geological hazard in Hebei Plain.This paper presents their temporal and spatial variations.The majority of earth fissures occur in alluvial-proluvial apron zone.Earth fissures express themselves at land surface as straight line,crenata,polygonal line and forniciform.The spatial distribution of ground fissures can be characterized as directional,cluster and systematic.Length and intensity of earth fissures also vary with time.The primary causes for earth fissuring includes earthquake activities,groundwater overdraft and ground collapse.
2006, 14(2): 184-189.
Through comprehensive study on a large amount of engineering examples,the primary failure causes of Guangdong expressway cut slopes in recent years,the concept of landslip prevention designing,slope treatment program,slope monitoring and slope emergency treatment measures are investigated. The investigation revealed that the instabilities of cut slopes are due to the adverse conditions in water and climate,strata,lithology,geology structure, human activities or engineering activities,etc..Therefore,a five-stage dynamic designing method is put forward,which consists of geologic mapping,engineering geological investigation,comprehensive analyses of slope stability,schematic designing,and detailed construction drawing designing.Finally,an actual case of slope stabilization is used to illustrate the dynamic designing method.
Through comprehensive study on a large amount of engineering examples,the primary failure causes of Guangdong expressway cut slopes in recent years,the concept of landslip prevention designing,slope treatment program,slope monitoring and slope emergency treatment measures are investigated. The investigation revealed that the instabilities of cut slopes are due to the adverse conditions in water and climate,strata,lithology,geology structure, human activities or engineering activities,etc..Therefore,a five-stage dynamic designing method is put forward,which consists of geologic mapping,engineering geological investigation,comprehensive analyses of slope stability,schematic designing,and detailed construction drawing designing.Finally,an actual case of slope stabilization is used to illustrate the dynamic designing method.
2006, 14(2): 190-195.
The faults activity appraisal is a foundation for study of regional tectonic stability because it directly affects the safety of a hydraulic engineering structure against seismic activity.Dating of fault gouge is now a common method for evaluation of faults activity,one of the quantitative methods.However,different dating methods tend to give different results even for the same fault gouge sample,which has caused concerns on the reliability of fault activity appraisal.In this paper,the author discusses some of problems in adduction of dating information of the fault gouge in hydropower projects and suggests methods for resolving the problems.A case study on the activity of Mabian-Yanjin,Lianfeng and Jinyang faults of the Xiluodu hydroelectric project is presented to demonstrate methods suggested by the author.
The faults activity appraisal is a foundation for study of regional tectonic stability because it directly affects the safety of a hydraulic engineering structure against seismic activity.Dating of fault gouge is now a common method for evaluation of faults activity,one of the quantitative methods.However,different dating methods tend to give different results even for the same fault gouge sample,which has caused concerns on the reliability of fault activity appraisal.In this paper,the author discusses some of problems in adduction of dating information of the fault gouge in hydropower projects and suggests methods for resolving the problems.A case study on the activity of Mabian-Yanjin,Lianfeng and Jinyang faults of the Xiluodu hydroelectric project is presented to demonstrate methods suggested by the author.
2006, 14(2): 196-199.
Saturated soft loess is a special soil in the loess area,Xi'an,China.This paper presents the surveying results ofthe saturated soft loess at the urban area and the northern railway area in Xi'an.The paper further presents and analyzes the spatial distribution and the physical properties of saturated soft loess.The differences between the spatial distributions of the two areas are discussed.The causes of forming the saturated soft loess in the two areas are examined.A hypothesis that there is saturated soft loess in the upper perched water zone is suggested.
Saturated soft loess is a special soil in the loess area,Xi'an,China.This paper presents the surveying results ofthe saturated soft loess at the urban area and the northern railway area in Xi'an.The paper further presents and analyzes the spatial distribution and the physical properties of saturated soft loess.The differences between the spatial distributions of the two areas are discussed.The causes of forming the saturated soft loess in the two areas are examined.A hypothesis that there is saturated soft loess in the upper perched water zone is suggested.
2006, 14(2): 200-205.
About 10 navigation control junctions of kiloton-class have been planned on the Yujiang river,Guangxi province.Three junctions,Laokou,Yuliang and Naji,are located in Tertiary basins where.rocks are mainly composed of mudstone.The mudstone is saturated and has the characteristics of low compressive strength,sensitive to environment change and weakly breakage.The mudstone would cause problems in terms of low bearing capacity,excessive deformation,low factor of safety,poor rock mass stability and high requirements for design and construction.Based on the investigation of the mudstones in Naji, Laokou and Yuliang junctions,the characteristics of the mudstones are examined in this paper.Effective evaluation methods and the corresponding engineering strategies for junction construction in the mudstone are put forward.They include assessment of engineering geology conditions,measures for checking criterion for mudstone foundation,foundation mudstone protection,and foundation treatment.
About 10 navigation control junctions of kiloton-class have been planned on the Yujiang river,Guangxi province.Three junctions,Laokou,Yuliang and Naji,are located in Tertiary basins where.rocks are mainly composed of mudstone.The mudstone is saturated and has the characteristics of low compressive strength,sensitive to environment change and weakly breakage.The mudstone would cause problems in terms of low bearing capacity,excessive deformation,low factor of safety,poor rock mass stability and high requirements for design and construction.Based on the investigation of the mudstones in Naji, Laokou and Yuliang junctions,the characteristics of the mudstones are examined in this paper.Effective evaluation methods and the corresponding engineering strategies for junction construction in the mudstone are put forward.They include assessment of engineering geology conditions,measures for checking criterion for mudstone foundation,foundation mudstone protection,and foundation treatment.
2006, 14(2): 206-211.
In order to assess the active zone depth and the cracking zone depth of expansive soil below ground surface,Mithchell formulation and crack expansion equation are used.Through excavating observation wells in two inartificial slopes in Ankang area,the suction values at different depths were measured by tensiometer.According to the Mithchell formulation,the active zone depth is calculated.According to the theory of tensile strength of unsaturated soil,the equation of crack expansion is formulated.The theoretical solution is obtained through calculation from the results of suction measurement.The results indicate that the suction curves of expansive soil do not change significantly with the increase of depth.The curves undulate with depth.The active zone depth of expansive soil is found to be between 3.17 m and 3.32 m.The crack depth is found to be between 3.06 m and 3.14 m.Therefore,the results of the two methods are close.
In order to assess the active zone depth and the cracking zone depth of expansive soil below ground surface,Mithchell formulation and crack expansion equation are used.Through excavating observation wells in two inartificial slopes in Ankang area,the suction values at different depths were measured by tensiometer.According to the Mithchell formulation,the active zone depth is calculated.According to the theory of tensile strength of unsaturated soil,the equation of crack expansion is formulated.The theoretical solution is obtained through calculation from the results of suction measurement.The results indicate that the suction curves of expansive soil do not change significantly with the increase of depth.The curves undulate with depth.The active zone depth of expansive soil is found to be between 3.17 m and 3.32 m.The crack depth is found to be between 3.06 m and 3.14 m.Therefore,the results of the two methods are close.
2006, 14(2): 212-215.
According to the test data of the thermal conductivity of large amounts of clay and silty clay samples in Nanjing,China,the relationships among the soil thermal conductivity and the moisture content and the void ratio are analyzed in this paper.Factors affecting the soil thermal conductivity are further analyzed.Finally,empirical formula is proposed for estimating the soil thermal conductivity from the soil moisture content and the soil void ratio.
According to the test data of the thermal conductivity of large amounts of clay and silty clay samples in Nanjing,China,the relationships among the soil thermal conductivity and the moisture content and the void ratio are analyzed in this paper.Factors affecting the soil thermal conductivity are further analyzed.Finally,empirical formula is proposed for estimating the soil thermal conductivity from the soil moisture content and the soil void ratio.
2006, 14(2): 216-222.
The electrical resistivity of soils is dependent on solid components,pore water,microstructure and environmental characteristics of soils.Therefore,electrical resistivity of soils is affected by various factors, including soil type,water content,saturation,temperature and pore fluid property et al.The soil electrical resistivity can be measured non-destructively by placing electrodes on the soil surface,applying a voltage and measuring the current.In the laboratory measurements of soil electrical resistivity,the number of electrodes(two electrodes or four electrodes),current types(DC or AC) and the frequency of the used AC should be considered.Practical aspects of these methods and arrangements are discussed in this paper.Based on the analyses of the theory of soil electrical resistivity and laboratory measuring techniques,the authors introduce a new practical device for the laboratory measurement of electrical resistivity,which uses two electrodes and lower frequency AC.Pilot test results show the equipment is effect and feasible in measurement of soil electrical resistivity.
The electrical resistivity of soils is dependent on solid components,pore water,microstructure and environmental characteristics of soils.Therefore,electrical resistivity of soils is affected by various factors, including soil type,water content,saturation,temperature and pore fluid property et al.The soil electrical resistivity can be measured non-destructively by placing electrodes on the soil surface,applying a voltage and measuring the current.In the laboratory measurements of soil electrical resistivity,the number of electrodes(two electrodes or four electrodes),current types(DC or AC) and the frequency of the used AC should be considered.Practical aspects of these methods and arrangements are discussed in this paper.Based on the analyses of the theory of soil electrical resistivity and laboratory measuring techniques,the authors introduce a new practical device for the laboratory measurement of electrical resistivity,which uses two electrodes and lower frequency AC.Pilot test results show the equipment is effect and feasible in measurement of soil electrical resistivity.
2006, 14(2): 223-228.
The treatment of laterite subsidence is important for a stability of a foundation.This paper presents dynamic compaction test results for treatment of thick-filling soil mass with a laterite base.Appropriate working procedures and design parameters are obtained from the test.Monitoring data show that the treatment offers good compacting effect as well as economic benefits.
The treatment of laterite subsidence is important for a stability of a foundation.This paper presents dynamic compaction test results for treatment of thick-filling soil mass with a laterite base.Appropriate working procedures and design parameters are obtained from the test.Monitoring data show that the treatment offers good compacting effect as well as economic benefits.
2006, 14(2): 229-232.
Foundation treatment is necessary when a structure is built over the soft clay ground.A composite foudation is one of effective reinforcement methods.In general,a project requires a higher bearing capacity in shallow soil and sufficient strength in deep soil to support the overlying soil layer.A long-short-pile composite foundation with a high replacement ratio in the shallow layer and lower one in the deep layer,satisfies demands for bearing capacity in soft foundation at diffenrent depths.Meanwhile,shallow composite modulus is high because of high replacement ratio,while deep composite modulus is low.As a result,high stresses will occur in the shallow soil and low stresses in deep one,which is a favorable distribution for decreacing total settlement of the soft foundation.A optimization mathematical model is developed and solved using complex method.A case study is given to demonstrate the optimization design method.The results show that the most reliable and economical design can be easily obtained from the presented method.
Foundation treatment is necessary when a structure is built over the soft clay ground.A composite foudation is one of effective reinforcement methods.In general,a project requires a higher bearing capacity in shallow soil and sufficient strength in deep soil to support the overlying soil layer.A long-short-pile composite foundation with a high replacement ratio in the shallow layer and lower one in the deep layer,satisfies demands for bearing capacity in soft foundation at diffenrent depths.Meanwhile,shallow composite modulus is high because of high replacement ratio,while deep composite modulus is low.As a result,high stresses will occur in the shallow soil and low stresses in deep one,which is a favorable distribution for decreacing total settlement of the soft foundation.A optimization mathematical model is developed and solved using complex method.A case study is given to demonstrate the optimization design method.The results show that the most reliable and economical design can be easily obtained from the presented method.
2006, 14(2): 233-238.
Selection of deformation parameters is very important in numerical computation and stability evaluation of the jointed rock masses engineering.When in-situ tests cant be made,an empirical method has to be used to estimate parameters to be used in simulation.This paper presents an improved empirical method for determination of deformation modulus for jointed rock masses based on many existing empirical methods commonly used in the world including size effect reduction and jointed character reduction of the intact rock specimen.Three case studies for dam sites and hydropower plants are presented as examples in the paper.
Selection of deformation parameters is very important in numerical computation and stability evaluation of the jointed rock masses engineering.When in-situ tests cant be made,an empirical method has to be used to estimate parameters to be used in simulation.This paper presents an improved empirical method for determination of deformation modulus for jointed rock masses based on many existing empirical methods commonly used in the world including size effect reduction and jointed character reduction of the intact rock specimen.Three case studies for dam sites and hydropower plants are presented as examples in the paper.
2006, 14(2): 239-244.
The deformation and stability of left bank slope B in Longtan Project is the key to safety of the project.Geologic and stability analyses indicate that overall stability of the left bank slope B depends on stability of the slope foot.Therefore,pressing slope foot is taken to stabilize the slope.Numerical simulation method of 3DEC(3D Discrete Element Code) is used to analyze stability of slope B in this paper.The results show: the pressing foot project can actively control the deformation of slope B.Numerical simulation results also match well with monitored displacement of the slope,which proves effectiveness of the pressing foot project on stabilizing the slope.
The deformation and stability of left bank slope B in Longtan Project is the key to safety of the project.Geologic and stability analyses indicate that overall stability of the left bank slope B depends on stability of the slope foot.Therefore,pressing slope foot is taken to stabilize the slope.Numerical simulation method of 3DEC(3D Discrete Element Code) is used to analyze stability of slope B in this paper.The results show: the pressing foot project can actively control the deformation of slope B.Numerical simulation results also match well with monitored displacement of the slope,which proves effectiveness of the pressing foot project on stabilizing the slope.
2006, 14(2): 245-248.
Field tests were carried out for examining active earth pressure zone near a deep and large foundation pit supported with piles and anchors.Based on the concept of spatial and temporal effect,the features of forces acting on the pile and anchor supporting system are studied and analyzed. The characteristics of the earth pressure in the active zone with respect to the pit excavation steps are obtained.The results can be a useful reference to the earth pressure calculation of similar deep and large foundation pits.
Field tests were carried out for examining active earth pressure zone near a deep and large foundation pit supported with piles and anchors.Based on the concept of spatial and temporal effect,the features of forces acting on the pile and anchor supporting system are studied and analyzed. The characteristics of the earth pressure in the active zone with respect to the pit excavation steps are obtained.The results can be a useful reference to the earth pressure calculation of similar deep and large foundation pits.
2006, 14(2): 249-252.
Due to some defects of BP neural network,the power size and the threshold value of the network structure are optimized by combining genetic algorithm with neural network.The estimation model of bolt bearing capacity is accordingly built based on the improved optimization algorithm.In this model,five low strain variables from dynamic testing are used to estimate the bolt bearing capacity.The calculated results are compared with those of BP neural network.The presented example shows that the genetic neural network is of both higher computing efficiency and higher identification accuracy in estimating the bolt bearing capacity.
Due to some defects of BP neural network,the power size and the threshold value of the network structure are optimized by combining genetic algorithm with neural network.The estimation model of bolt bearing capacity is accordingly built based on the improved optimization algorithm.In this model,five low strain variables from dynamic testing are used to estimate the bolt bearing capacity.The calculated results are compared with those of BP neural network.The presented example shows that the genetic neural network is of both higher computing efficiency and higher identification accuracy in estimating the bolt bearing capacity.
2006, 14(2): 253-256.
In this paper,the authors use two-D elastic-plastic FEM software to analyze the stability of the ANA tunnel in CHANG-JI highway.The internal force and displacement of surrounding rock are calculated.The deformation behavior is also analyzed.The results presented in this paper provide guidelines for design and construction of similar tunnels.
In this paper,the authors use two-D elastic-plastic FEM software to analyze the stability of the ANA tunnel in CHANG-JI highway.The internal force and displacement of surrounding rock are calculated.The deformation behavior is also analyzed.The results presented in this paper provide guidelines for design and construction of similar tunnels.
2006, 14(2): 257-262.
The Chongwenmen station of Beijing metro line No.5 goes beneath the existing subway line No.1.In order to guarantee the normal operation of the existing metro line and the safety of underground construction,the stratum displacement caused by construction must be well controlled.This paper presents the analysis of allowable ground subsidence during construction the Chongwenmen station project.In order to control the ground subsidence and guarantee the safety of construction,big pipe umbrella of small rigidity or pipejacking of greater rigidity is used as pre-support.In this paper,three-dimensional finite element software,3D-Sigma,is used to simulate effects of the construction and estimate the subsidence of the interval tunnel caused by the construction.At the end,effects of big pipe umbrella and pipejacking pre-support are analyzed and compared,which can provide guidelines for selection of appropriate presupport scheme.
The Chongwenmen station of Beijing metro line No.5 goes beneath the existing subway line No.1.In order to guarantee the normal operation of the existing metro line and the safety of underground construction,the stratum displacement caused by construction must be well controlled.This paper presents the analysis of allowable ground subsidence during construction the Chongwenmen station project.In order to control the ground subsidence and guarantee the safety of construction,big pipe umbrella of small rigidity or pipejacking of greater rigidity is used as pre-support.In this paper,three-dimensional finite element software,3D-Sigma,is used to simulate effects of the construction and estimate the subsidence of the interval tunnel caused by the construction.At the end,effects of big pipe umbrella and pipejacking pre-support are analyzed and compared,which can provide guidelines for selection of appropriate presupport scheme.
2006, 14(2): 263-270.
The consolidation method by exploding is a new treatment technique in soft soil ground.To analyze the variation of the exploding effect in ground,this paper presents numerical simulation of single hole powder exploding in soft ground through finite element method.On the basis of verifying the result of calculation with that of in situ measurement,the paper examines the main affected zones in the soil due to powder exploding in single hole.Different cover pressure and explosive dosage are further studied.For the problem of single hole powder exploding in soil,the ALE algorithm is used to resolve the aberrance of mesh.The result indicates that the time for the cover pressure taking effect was after an exploding,not on the exploding.Dissipation of pore water is the most contributing factor for the effectiveness.The explosive dosage has important influence on the spacing of holes and vertical drainage channels.
The consolidation method by exploding is a new treatment technique in soft soil ground.To analyze the variation of the exploding effect in ground,this paper presents numerical simulation of single hole powder exploding in soft ground through finite element method.On the basis of verifying the result of calculation with that of in situ measurement,the paper examines the main affected zones in the soil due to powder exploding in single hole.Different cover pressure and explosive dosage are further studied.For the problem of single hole powder exploding in soil,the ALE algorithm is used to resolve the aberrance of mesh.The result indicates that the time for the cover pressure taking effect was after an exploding,not on the exploding.Dissipation of pore water is the most contributing factor for the effectiveness.The explosive dosage has important influence on the spacing of holes and vertical drainage channels.
COMPARISON OF SOIL NAIL AND COMPOSITE SOIL NAIL REINFORCEMENT STRUCTURES USING NUMERICAL SIMULATIONS
2006, 14(2): 271-275.
Foundation pits.In this paper,the authors use SnEpFem software to evaluate several alternative soil nail reinforcement structures: soil nail along,pre-stressed anchor plus soil nail;miniature pile plus soil nail;and miniature pile,pre-stressed anchor plus soil nail.Comparison of all four alternatives is done for the characteristics of horizontal deflections,ground surface settlements and the range of settlement,pit bottom uplifts and the areas of tension and plastic zones.It was concluded that(1) Compared with simple soil nail reinforcement structure,composite soil nail reinforcement can control slope distortion in effect,and reduce the areas of tension and plastic zones.Consequently,composite soil nail reinforcement structures can improve slope stability.(2) Setting miniature pile controls horizontal deflections better than adding pre-stress.(3) Setting miniature pile can efficiently control ground surface settlements,however,adding pre-stress influences it a little.(4) The effect for pit bottom uplifts is consistent in all the reinforcement structures,and the values vary a bit.By comparison,under this engineering geologic condition, of all the composite soil nail reinforcement structures,the most dependable one is miniature pile + pre-stressed anchor + soil nail reinforcement structure.Its distortion,settlement and the areas of tension and plastic zones are least in the four structures,and it is the most excellent reinforcement structure.
Foundation pits.In this paper,the authors use SnEpFem software to evaluate several alternative soil nail reinforcement structures: soil nail along,pre-stressed anchor plus soil nail;miniature pile plus soil nail;and miniature pile,pre-stressed anchor plus soil nail.Comparison of all four alternatives is done for the characteristics of horizontal deflections,ground surface settlements and the range of settlement,pit bottom uplifts and the areas of tension and plastic zones.It was concluded that(1) Compared with simple soil nail reinforcement structure,composite soil nail reinforcement can control slope distortion in effect,and reduce the areas of tension and plastic zones.Consequently,composite soil nail reinforcement structures can improve slope stability.(2) Setting miniature pile controls horizontal deflections better than adding pre-stress.(3) Setting miniature pile can efficiently control ground surface settlements,however,adding pre-stress influences it a little.(4) The effect for pit bottom uplifts is consistent in all the reinforcement structures,and the values vary a bit.By comparison,under this engineering geologic condition, of all the composite soil nail reinforcement structures,the most dependable one is miniature pile + pre-stressed anchor + soil nail reinforcement structure.Its distortion,settlement and the areas of tension and plastic zones are least in the four structures,and it is the most excellent reinforcement structure.
2006, 14(2): 281-287.
Geo-synthetics is one kind of important material in geotechnical construction.To use it in the bank protection engineering by using geo-synthetics,soil retention criterion of geo-textile should be assessed.Based on case studies of bank protection projects,lab tests,in-situ tests,locale antitypes tests and observations,and theoretical analysis the authors recommend a new soil retention criterion of textile,O90（210）d90,which challenges the existing criterion of O90（12）d90 that adopted by all the world will be challenged.
Geo-synthetics is one kind of important material in geotechnical construction.To use it in the bank protection engineering by using geo-synthetics,soil retention criterion of geo-textile should be assessed.Based on case studies of bank protection projects,lab tests,in-situ tests,locale antitypes tests and observations,and theoretical analysis the authors recommend a new soil retention criterion of textile,O90（210）d90,which challenges the existing criterion of O90（12）d90 that adopted by all the world will be challenged.
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