Effects of Initial Shear Stress on Cyclic Behavior of Saturated Soft Clay

Abstract

The cyclic behaviors of Hangzhou soft clay subjected to initial shear stress are investigated through undrained cyclic triaxial tests. It is observed that the cyclic strength of soft clay degrades fairly rapidly with the number of failure cycles when there is no initial shear stress. However, the cyclic strength degrades lesser when there is an initial shear stress. The cyclic strength decreases and the total cyclic strength increases as initial shear stress is increased. High rates of stiffness degradation and strain softening are evident in the test with initial shear stress lower than cyclic stress. However, no stiffness degradation or strain softening can be observed in the test with initial shear stress higher than cyclic stress. In a semi-log scale, the relationship between degradation index and cyclic number shows a strong non-linearity. This relationship has been synthesized in the form of an empirical equation by introducing a normalized cyclic stress parameter. The empirical equation, together with the mean axial strain equation is further incorporated into the modified Iwan's model to simulate the stress-strain relationship of soft clay subjected to initial shear stress. A comparison between experimental and predicted stress-strain curves shows a good agreement.