复杂循环荷载作用后长江口原状淤泥质软黏土静强度弱化特性研究

利用土工静力–动力液压三轴–扭转多功能剪切仪, 针对取自于长江口的海洋原状淤泥质软黏土，在不固结不排水条件下，分别进行了动三轴、45°线耦合以及圆耦合等多种复杂循环剪切试验及循环荷载作用后静三轴试验。结果表明，随着循环次数的增加，三种不同模式循环荷载作用产生的应变、孔压增量以及循环荷载作用后土的静强度衰减程度差异均变得越来越明显。对应相同循环剪切次数，双向耦合循环剪切要大于单向循环剪切产生的应变与孔压增量，双向耦合循环剪切后静强度衰减更加明显；而对于双向耦合循环剪切，圆耦合循环剪切大于45°线耦合循环剪切产生的应变与孔压增量，并且圆耦合循环剪切后静强度衰减更加显著。由此表明，主应力轴连续旋转会使土体产生更大的变形与孔压增量，并且使静强度显著降低。分别定义了广义综合剪应变及综合孔压增量比，并建议了循环荷载作用后静强度与广义综合剪应变、综合孔压增量比的关系。

Study on the degradation of static shear strength of undisturbed silty soft clay in the yangtze estuary after complex cyclic loadings

Using the geotechnical static and dynamic universal triaxial and torsional shear apparatus, the undisturbed marine silty soft clay in the yangtze estuary is tested under unconsolidated-undrained conditions, with the dynamic triaxial, 45° line coupling/circle coupling complex cyclic shear tests and the static triaxial tests after cyclic loadings. It is found that the differences of the strains and the pore water pressure increments caused by three different modes of cyclic loadings become more pronounced with increase of the number of cycles as well as the degradation degrees of static shear strength after cyclic loadings. After the same number of cyclic shear, the strain and pore water pressure increment caused by bidirectional coupling cyclic shear are larger than those caused by monodirectional cyclic shear and the degradation degree of static shear strength after bidirectional coupling cyclic shear become more evident; As for bidirectional coupling cyclic shear, the strain and pore water pressure increment caused by circle coupling cyclic shear are larger than those caused by 45° line coupling cyclic shear and the degradation degree of static shear strength after circle coupling cyclic shear is more significant. This indicates that continuous rotation of principal stress direction makes larger strain and pore water pressure increment and reduces the static shear strength remarkably. The generalized synthetic shear strain and the synthetic pore water pressure incremental ratio are defined respectively and the relationships between static shear strength and generalized synthetic shear strain, shear strength and synthetic pore water pressure incremental ratio are proposed.