Experimental Study On The Static And Cyclic Behavior Of Overconsolidated Clay Uner Various Initial Shear Stress

In many practical geotechnical applications,due to the large numbers of repeated cyclic loading,fluctuation of the groundwater-level or the surcharge preloading method in engineering practice,soils in the shallow layers are always overconsolidated.For the soft subsoil involving embankment,earth dams and slopes,the soil elements are subjected to static shear stresses on the horizontal planes before the cyclic loading comes into effect.Under the combined influence of cyclic loading and initial shear stress,obvious strain and pore pressure will accumulate,which will lead to the degradation of the stiffness and strength of the soil and the destruction of the foundation soil structure.In order to solve the above problems,the purpose of this paper is to study the effects of initial static shear stress on overconsolidated soft clay.A series of undrained monotonic and cyclic triaxial tests were performed with various OCR under varying combinations of the initial static shear stress and cyclic deviator stresses to simulate level ground and sloping ground conditions,the accumulated axial strain,excess pore pressure,stress-strain hysteresis,stiffness degradation were investigated.The influence of initial stress decreases with the increase of OCR,because the undrained shear strength was strengthened by the overconsolidation process,which made the specimen more resistant to the influence of cyclic loading.Thus,even under high initial shear stress,the highly overconsolidated specimen will not approach failure.With the application of initial shear stress,the effective stress path moved upwards and was closer to the CSL line,the specimen is easier to approach failure.In this paper,the threshold initial shear stress level is proposed,when initial shear stress is greater than the threshold value,the axial strain increases rapidly and the specimen approached failure within small number of cycles,below which the axial strain increases with the increase of the number of cycles,the development rate becomes slower,and there is no obvious deformation occurs after long-term cyclic loading.