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EXPERIMENTAL RESEARCH ON CHANGING RULES OF DYNAMIC MODULUS AND DAMPING RATIO OF SATURATED SOFT CLAY UNDER BIDIRECTIONAL EXCITING CYCLIC LOADING

Dynamic modulus and damping ratio of saturated soft clay under bidirectional cyclic loading are investigated by GDS dynamic triaxial system. It is observed that the pore water pressure ratio increases significantly with the increase of radial cyclic stress ratio. Radial cyclic stress has great effect on initial pore water pressure;and the increase of initial pore water pressure is approximately equal to the radial cyclic stress. The threshold of cyclic stress ratio changes little under bidirectional cyclic loading. The dynamic modulus and damping ratio are affected by radial cyclic stress significantly. By increasing the radial cyclic stress,the damping ratio increases while the dynamic modulus decreases. Small strain elastic modulus decreases as the radial cyclic stress increases and there is a linear relation between the small strain elastic modulus and the radial cyclic stress ratio. An empirical model for the small strain elastic modulus is obtained based on the modification of Hardin equation. The radial cyclic stress and confining pressure have little effect on the curves of ( Ed / Ed max)- e d and ( D / Dm ax)- e d. By modifying hyperbolic model,the empirical models for describing the change of dynamic modulus and damping with dynamic strain are obtained.