波浪荷载作用后软黏土静强度弱化及软基加固研究

Study of degradation of static shear strength of soft clay after wave loading and consolidation of soft foundation

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饱和淤泥质软黏土,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;通过室内试验模拟堆载预压加固软基,并针对加固后土体进行了上述系列试验.结果表明,对应相同循环剪切次数,双向耦合大于单向循环剪切产生的应变与孔压增量,双向循环荷载作用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,且剪切后静强度衰减更加显著.土体经过加固处理后,循环剪切产生的应变明显变小,而且循环应变要较累积应变表现得更为突出;孔压的累积效应要比循环效应更加显著,并且循环荷载作用后静强度衰减程度明显降低,表明土体经加固处理后抵抗循环荷载弱化能力得到极大增强.长江口导堤的重建工程证明了试验结果的可靠性并说明了该研究具有的重要工程应用价值.

The soil static and dynamic universal triaxial and torsional shear apparatus was employed to perform experimental tests of the undisturbed saturated marine silt soft clay in the Yangtze estuary.Under unconsolidated-undrained conditions,the dynamic triaxial,45° line coupling as well as circle coupling complex cyclic shear tests and the static triaxial tests after cyclic loadings were carried out.The laboratory tests were carried out to simulate the consolidation treatment of soft foundation with the preloading method.Likewise,a series of above-mentioned tests were carried out.The experimental results show that,corresponding to 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 cyclic loadings 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.For the soils after consolidation treatment,the strains caused by cyclic shear become smaller evidently and the cyclic strains are more significant than the cumulative one.The cumulative effect is more remarkable than the cyclical effect on the pore water pressure.The shear strengths after cyclic loadings are not reduced so remarkably,which indicates that the cyclic loading resistance is enhanced greatly after consolidation.The reconstruction project of the guide dike in Yangtze estuary verifies the reliability of the test results and shows that this study has important value for engineering application.