Research On The Bearing Capacity Of Soft Clay Foundations Considering The Weakening Effect Under Cyclic Loading

In recent years,China's port construction develops very fast,and tends to be larger and deeper.As a result,the higher stability of the foundation is required.However,China's coastal and offshore areas widespread distribution of soft clay,whose physical and mechanical properties are poor,furthermore,the soft clay weaken under cyclic loading,such as waves.Therefore,it reduces the bearing capacity of foundations.In order to solve the problems,many triaxial tests and numerical simulations on muddy-silty clay taken from Yantai littoral zone are finished,and the bearing capacity of soft clay foundations considering the weakening effect under cyclic loading is studied.The main contents are abstracted as follows:(1)Static and dynamic triaxial tests are finished,and the accumulative pore pressure development and the accumulative deformation development subjected to different consolidation confining stress,consolidation deviator stress,dynamic stress and cycle times are analyzed.After the data fitting,the modified hyperbolic calculation models of the accumulative pore pressure development and the accumulative deformation are put forward.(2)According to the test results,the undrained shear strength development is analyzed.In the process of anisotropic consolidation,the strength increase is influenced by the consolidation confining stress and the consolidation deviator stress.In the process of cyclic loading,the strength weakening is influenced by the consolidation confining stress,the consolidation deviator stress,the dynamic stress and the cycle times,and a modified calculation model of the strength weakening is put forward.Based on the above models,a calculation model of the strength development is generated.(3)Based on the engineering practice,a finite element model of the caisson breakwater is established in ABAQUS.With a method of secondary development in ABAQUS,a user subroutine named USDFLD is programmed to combine the strength development model into the finite element model,so that the strength development in the soft clay foundation can be expressed in the process of anisotropic consolidation and cyclic loading.The analysis shows that,for caisson breakwaters,the weakening effect under cyclic loading can be reduced greatly by the anisotropic consolidation,so the weakening effect can be ignored.(4)Using modified the finite element model,the strength development in the soft clay foundation is studied considering the infuences of different horizontal wave loading,vertical wave loading,sand filling quantity in the breakwater,width of foundation and thickness of clay replacement.Then,for different loading condition,two formulas of the safety factor on foundation bearing capacity are put forward.At last,some effective suggestions were given to solve engineering problems.