In order to investigate the compressibility, particularly the secondary compression behaviour, soil structure and undrained shear strength of Shanghai Clay, a series of one-dimensional consolidation tests （some up to...In order to investigate the compressibility, particularly the secondary compression behaviour, soil structure and undrained shear strength of Shanghai Clay, a series of one-dimensional consolidation tests （some up to 70 d） and undrained triaxial tests on high-quality intact and reconstituted soil specimens were carried out. Shanghai Clay is a lightly overconsolidated soil （OCR=1.2-1.3） with true cohesion or bonding. Due to the influence of soil structures, the secondary compression index Ca varies significantly with consolidation stress and the maximum value of C~ occurs in the vicinity of preconsolidation stress. Measured coefficients of secondary compression generally fall in the range of 0.2%-0.8% based on which Shanghai Clay can be classified as a soil with low to medium secondary compressibility. The effect of soil structures on the compressibility of Shanghai Clay is found to reduce with an increase in depth. Soil structure has an important influence on initial soil stiffness, but does not appear to affect undrained shear strength significantly. Undrained shear strengths of intact Shanghai Clay from compression tests are approximately 20% higher than those from extension tests.展开更多
The joint of clay core-wall and concrete cut-off wall is one of the weakest parts in high earth and rockftll dams.A kind of highly plastic clay is always fixed on the joint to fit the large shear deformation between c...The joint of clay core-wall and concrete cut-off wall is one of the weakest parts in high earth and rockftll dams.A kind of highly plastic clay is always fixed on the joint to fit the large shear deformation between clay core-wall and concrete cut-offwall,so the hydro-mechanical coupling mechanisms on the joint under high stress,high hydraulic gradient,and large shear deformation are of great importance for the evaluation of dam safety.The hydro-mechanical coupling characteristics of the joint of the highly plastic clay and the concrete cut-off wall in a high earth and rockfill dam in China were studied by using a newly designed soil-structure contact erosion apparatus.The experimental results indicate that：1） Shear failure on the joint is due to the hydro-mechanical coupling effect of stress and seepage failure.The seepage failure will induce the final shear failure when the ratio of deviatoric stress to confining pressure is within 1.0-1.2; 2） A negative exponential permeability empirical model for the joint denoted by a newly defined principal stress function,which considers the coupling effect of confining pressure and axial pressure on the permeability,is established based on hydro-mechanical coupling experiments.3） The variation of the settlement before and after seepage failure is very different.The settlement before seepage failure changes very slowly,while it increases significantly after the seepage failure.4） The stress-strain relationship is of a strain softening type.5） Flow along the joint still follows Darcian flow rule.The results will provide an important theoretical basis for the further evaluation on the safety of the high earth and rockfill dam.展开更多
基金Project(GRF618006) supported by the Research Grants Council of the Hong Kong Special Administrative Region, China
文摘In order to investigate the compressibility, particularly the secondary compression behaviour, soil structure and undrained shear strength of Shanghai Clay, a series of one-dimensional consolidation tests （some up to 70 d） and undrained triaxial tests on high-quality intact and reconstituted soil specimens were carried out. Shanghai Clay is a lightly overconsolidated soil （OCR=1.2-1.3） with true cohesion or bonding. Due to the influence of soil structures, the secondary compression index Ca varies significantly with consolidation stress and the maximum value of C~ occurs in the vicinity of preconsolidation stress. Measured coefficients of secondary compression generally fall in the range of 0.2%-0.8% based on which Shanghai Clay can be classified as a soil with low to medium secondary compressibility. The effect of soil structures on the compressibility of Shanghai Clay is found to reduce with an increase in depth. Soil structure has an important influence on initial soil stiffness, but does not appear to affect undrained shear strength significantly. Undrained shear strengths of intact Shanghai Clay from compression tests are approximately 20% higher than those from extension tests.
基金Projects(51009053,51079039)supported by the National Natural Science Foundation of ChinaProject(20100094120004)supported by the Doctoral Program of Higher Education of China
文摘The joint of clay core-wall and concrete cut-off wall is one of the weakest parts in high earth and rockftll dams.A kind of highly plastic clay is always fixed on the joint to fit the large shear deformation between clay core-wall and concrete cut-offwall,so the hydro-mechanical coupling mechanisms on the joint under high stress,high hydraulic gradient,and large shear deformation are of great importance for the evaluation of dam safety.The hydro-mechanical coupling characteristics of the joint of the highly plastic clay and the concrete cut-off wall in a high earth and rockfill dam in China were studied by using a newly designed soil-structure contact erosion apparatus.The experimental results indicate that：1） Shear failure on the joint is due to the hydro-mechanical coupling effect of stress and seepage failure.The seepage failure will induce the final shear failure when the ratio of deviatoric stress to confining pressure is within 1.0-1.2; 2） A negative exponential permeability empirical model for the joint denoted by a newly defined principal stress function,which considers the coupling effect of confining pressure and axial pressure on the permeability,is established based on hydro-mechanical coupling experiments.3） The variation of the settlement before and after seepage failure is very different.The settlement before seepage failure changes very slowly,while it increases significantly after the seepage failure.4） The stress-strain relationship is of a strain softening type.5） Flow along the joint still follows Darcian flow rule.The results will provide an important theoretical basis for the further evaluation on the safety of the high earth and rockfill dam.
