CONSTITUTIVE EQUATION FOR CYCLIC BEHAVIOR OF COHESIVE SOILS.

Endochronic theory is employed to develop a relatively general constitutive relationship to model the dynamic behavior of cohesive soils subjected to multi-dimensional stress or strain paths. The proposed constitutive law is capable of describing strain softening and hardening, densification and dilatancy, frictional aspects, and rate dependence of the stress-strain behavior; it also accounts for pore pressure response in undrained conditions by considering saturated soils as two-phase media. The theory is based on a series of new internal state variables that are defined in terms of semi-empirical intrinsic material relationships, and it is able to handle elastic and inelastic strain histories for rate-dependent materials from the very beginning of their cyclic stress-strain path. The intrinsic relations involve ten material parameters, including the initial elastic modulus, which must be determined from a quasi-static and cyclic tests. The mathematical model is applied to describe data from low-frequency cyclic constant-strain-rate tests on undisturbed samples and low-frequency cyclic constant-load-amplitude tests on slurry-consolidated samples of kaolin.