A method of predicting the consolidation settlement-time curve of floating soil-cement column on improved soft clayey subsoil has been proposed.The degree of the consolidation(U(t))of the system is calculated by the d...A method of predicting the consolidation settlement-time curve of floating soil-cement column on improved soft clayey subsoil has been proposed.The degree of the consolidation(U(t))of the system is calculated by the double soil-layer consolidation theory,and the methods for evaluating the equivalent hydraulic conductivity(k)and the coefficient of volume compressibility(mv)of the part of the column improved layer have been proposed.The effectiveness of the method was verified by comparing predictions with the results of finite element analysis(FEA)using a unit cell model.The consolidation settlement(s(t))can be calculated by the method of treating a part of the column improved layer as an unimproved layer and using the corresponding average U(t)value.By comparing the predicted results with the measurements of laboratory model tests and three case histories in Fukuoka,Japan,the effectiveness of the proposed methods has been verified.It is suggested that the method can be used for designing the soft clayey subsoil improvement using floating soil-cement columns.展开更多
The effect of pore water chemistry on anisotropic behavior of consolidation and shear strength of reconstituted Ariake clay has been investigated experimentally.Two types of chemicals added into the pore water of the ...The effect of pore water chemistry on anisotropic behavior of consolidation and shear strength of reconstituted Ariake clay has been investigated experimentally.Two types of chemicals added into the pore water of the soil for enhancing flocculation microstructure of soil particles are sodium chloride(salt)(NaCl),and calcium chloride(CaCl_(2));and two dispersants added are sodium triphosphate(Na_(5)-P_(3)O_(10))and sodium hexametaphosphate(Na_(6)P_(6)O_(18)),respectively.The concentrations of these chemicals in pore water were 2-3%.Degrees of anisotropy of the coefficient of consolidation and undrained shear strength decreased with adding NaCl and CaCl_(2),but increased with adding the dispersants.Degree of anisotropy also increased with one-dimensional(1D)deformation and the samples with dispersive additives had higher increase rate.It has been confirmed qualitatively by scanning electron microscopy(SEM)images that adding dispersive chemicals promoted the formation of dispersive microstructure and increased the degree of anisotropy,and the chemicals enhancing flocculent microstructure had an inverse effect.The possible application of the findings to underground construction has been discussed also.展开更多
In this study,a deep excavation in an under-consolidated deposit in Zhuhai,China,was reported and investigated via plane strain finite element analysis(FEA).First,the project was simulated via FEA(under-consolidated d...In this study,a deep excavation in an under-consolidated deposit in Zhuhai,China,was reported and investigated via plane strain finite element analysis(FEA).First,the project was simulated via FEA(under-consolidated deposit),and a reasonable agreement between the lateral displacement of the measured and simulated retaining wall was obtained.Another FEA was then conducted under the assumption that the deposit was in a normally consolidated state.The numerical results indicate that the under-consolidated case resulted in a 25% increase in maximum lateral displacement of the contiguous pile-formed retaining wall,a 32% increase in bending moment in the wall,and approximately twice the maximum surface settlement behind the wall,when compared with those of the normally consolidated case.The main reasons for this are as follows:(1)the under-consolidated deposit was weaker,and(2)the ongoing consolidation of the under-consolidated deposit induced green-field settlement(approximately 4 mm)during the project period,thereby enhancing the bending deformation of the wall.Therefore,when designing deep excavation in an under-consolidated deposit,not only its weaker strength but also the negative effect of green-field settlement during the project period should be considered.展开更多
Methods for estimating the overconsolidation ratio(OCR)of soil deposits from piezocone sounding results have been investigated.Three existing methods have been briefly reviewed and a new method has been proposed.The p...Methods for estimating the overconsolidation ratio(OCR)of soil deposits from piezocone sounding results have been investigated.Three existing methods have been briefly reviewed and a new method has been proposed.The proposed method can be applied to both normally consolidated/overconsolidated and underconsolidated deposits.Furthermore,existing methods have been modified so that they can be applied to underconsolidated deposits.Then,all the methods have been applied to 12 case histories collected from 6 different countries.The estimated values of OCR have been compared with the measured data.It has been shown that if the parameters(soil properties and empirical parameters)can be determined appropriately,then all the methods can achieve a reasonable prediction.It has also been shown that the proposed method exhibits a relatively better performance and results in less scattered data than the other methods.展开更多
A road cave-in accident caused by tunneling is described,and the possible mechanism of failure is analyzed.The cave-in measured about 30 m×27 m in plane,and about 15 m in depth.At about 19 m below the ground surf...A road cave-in accident caused by tunneling is described,and the possible mechanism of failure is analyzed.The cave-in measured about 30 m×27 m in plane,and about 15 m in depth.At about 19 m below the ground surface at the site,a tunnel construction was underway.Immediately above the tunnel,there was a weathered shale layer approximately t 2.66 m thick;above this layer,there were sand and gravel layers.The groundwater level was estimated to be about 5 m below the ground surface.By arch analysis,it is shown that the most likely cause of the accident was the low strength of the weathered shale layer and the high water pressure above the tunnel,which resulted in tensile failure of the weathered shale layer.The All Ground Fasten(AGF)pre-support measure was adopted,but it might make very limited contribution to the increase in the tensile strength of the shale layer in the cross-sectional direction of the tunnel.展开更多
文摘A method of predicting the consolidation settlement-time curve of floating soil-cement column on improved soft clayey subsoil has been proposed.The degree of the consolidation(U(t))of the system is calculated by the double soil-layer consolidation theory,and the methods for evaluating the equivalent hydraulic conductivity(k)and the coefficient of volume compressibility(mv)of the part of the column improved layer have been proposed.The effectiveness of the method was verified by comparing predictions with the results of finite element analysis(FEA)using a unit cell model.The consolidation settlement(s(t))can be calculated by the method of treating a part of the column improved layer as an unimproved layer and using the corresponding average U(t)value.By comparing the predicted results with the measurements of laboratory model tests and three case histories in Fukuoka,Japan,the effectiveness of the proposed methods has been verified.It is suggested that the method can be used for designing the soft clayey subsoil improvement using floating soil-cement columns.
基金Mr.A.Saito,technician at the Graduate School of Science and Engineering,Saga University,Japan and Mr.T.Shimizu,graduate of the Faculty of Science and Engineering,Saga University conducted the direct shear tests reported in this study.This work has been supported by the National Natural Science Foundation of China(NSFC)with a grant No.51578333the Grants-in-Aid for Scientific Research(KAKENHI)of the Japanese Society for the Promotion of Science(JSPS)with a grant number of 15K06212.
文摘The effect of pore water chemistry on anisotropic behavior of consolidation and shear strength of reconstituted Ariake clay has been investigated experimentally.Two types of chemicals added into the pore water of the soil for enhancing flocculation microstructure of soil particles are sodium chloride(salt)(NaCl),and calcium chloride(CaCl_(2));and two dispersants added are sodium triphosphate(Na_(5)-P_(3)O_(10))and sodium hexametaphosphate(Na_(6)P_(6)O_(18)),respectively.The concentrations of these chemicals in pore water were 2-3%.Degrees of anisotropy of the coefficient of consolidation and undrained shear strength decreased with adding NaCl and CaCl_(2),but increased with adding the dispersants.Degree of anisotropy also increased with one-dimensional(1D)deformation and the samples with dispersive additives had higher increase rate.It has been confirmed qualitatively by scanning electron microscopy(SEM)images that adding dispersive chemicals promoted the formation of dispersive microstructure and increased the degree of anisotropy,and the chemicals enhancing flocculent microstructure had an inverse effect.The possible application of the findings to underground construction has been discussed also.
基金financially sponsored by National Foreign Experts and Talents Project of China(G20190009128)the Consulting Project on Hengqin Foundation Pits(CSCEC2B-SZ-HQKA-ZY-080)Shanghai Municipal Science and Technology Major Project(2017SHZDZX02),China.
文摘In this study,a deep excavation in an under-consolidated deposit in Zhuhai,China,was reported and investigated via plane strain finite element analysis(FEA).First,the project was simulated via FEA(under-consolidated deposit),and a reasonable agreement between the lateral displacement of the measured and simulated retaining wall was obtained.Another FEA was then conducted under the assumption that the deposit was in a normally consolidated state.The numerical results indicate that the under-consolidated case resulted in a 25% increase in maximum lateral displacement of the contiguous pile-formed retaining wall,a 32% increase in bending moment in the wall,and approximately twice the maximum surface settlement behind the wall,when compared with those of the normally consolidated case.The main reasons for this are as follows:(1)the under-consolidated deposit was weaker,and(2)the ongoing consolidation of the under-consolidated deposit induced green-field settlement(approximately 4 mm)during the project period,thereby enhancing the bending deformation of the wall.Therefore,when designing deep excavation in an under-consolidated deposit,not only its weaker strength but also the negative effect of green-field settlement during the project period should be considered.
基金The field data of Saga site have been provided by the Ariake Sea Coastal Road Development Office(ASCRDO),Saga Prefecture,Japan.This research is partially funded by the International Science and Technology Cooperation Program of China,with a grant number of 2015DFA71550Grants-in-Aid for Scientific Research(KAKENHI)of Japan Society for the Promotion of Science(JSPS)with grant number of 15K06212.
文摘Methods for estimating the overconsolidation ratio(OCR)of soil deposits from piezocone sounding results have been investigated.Three existing methods have been briefly reviewed and a new method has been proposed.The proposed method can be applied to both normally consolidated/overconsolidated and underconsolidated deposits.Furthermore,existing methods have been modified so that they can be applied to underconsolidated deposits.Then,all the methods have been applied to 12 case histories collected from 6 different countries.The estimated values of OCR have been compared with the measured data.It has been shown that if the parameters(soil properties and empirical parameters)can be determined appropriately,then all the methods can achieve a reasonable prediction.It has also been shown that the proposed method exhibits a relatively better performance and results in less scattered data than the other methods.
基金funded by National Key Basic Research Program of China(973 Program:2015CB057802).
文摘A road cave-in accident caused by tunneling is described,and the possible mechanism of failure is analyzed.The cave-in measured about 30 m×27 m in plane,and about 15 m in depth.At about 19 m below the ground surface at the site,a tunnel construction was underway.Immediately above the tunnel,there was a weathered shale layer approximately t 2.66 m thick;above this layer,there were sand and gravel layers.The groundwater level was estimated to be about 5 m below the ground surface.By arch analysis,it is shown that the most likely cause of the accident was the low strength of the weathered shale layer and the high water pressure above the tunnel,which resulted in tensile failure of the weathered shale layer.The All Ground Fasten(AGF)pre-support measure was adopted,but it might make very limited contribution to the increase in the tensile strength of the shale layer in the cross-sectional direction of the tunnel.
