CONSTITUTIVE MODEL FOR CYCLIC BEHAVIOR OF CLAYS .1. THEORY

One of the main objectives of the present paper and its companion. part II. is to develop an integrated approach in which various factors relevant to the cyclic behavior of piles can be simulated in a unified manner. They include fundamental constitutive models for cyclic loading appropriate laboratory tests, determination of material constants, validation of the model, and field verification, Development and verification of the constitutive model are described in part I. Here the hierarchical single surface (HiSS) plasticity-based concept is modified to allow for the cyclic response of a clay that occurs at Sabine Pass, Texas, where the field pile load tests were performed. The new series of delta* models allows for hardening, normal consolidation and overconsolidation, general stress paths, and fluid pressures. Special procedures are developed to identify and to determine parameters for the models. Triaxial tests performed on undisturbed specimens of Sabine clay are used to find the parameters. The model is then validated by comparing predictions with laboratory observations. Verifications of field pile-load tests using the model in a finite-element procedure including simulation of various stages such as in situ stress, driving, consolidation, tension, and cyclic load tests are presented in part II.