Isotach Elastoplasticity: A Case Study on Osaka Bay Clay

Abstract

The theory of isotach elastoplasticity (IEP) is applied to investigate the strain rate and time effects in Osaka Bay clay from Japan. The IEP theory considers geomaterials like clays as an overdamped oscillatory physical system, for which the strain rate (analogous to the vibration frequency) decays in an exponential manner. This feature can be captured by a characteristic strain rate and time relationship. The evolutionary change of strain rate is found to affect the mechanical response of soft clays in an isotach manner. A loading–isotach (LI) yield curve is proposed in the stress and strain rate plane. Combination of the characteristic strain rate and time relationship in an isotach manner into the framework of critical state soil mechanics renders an isotach (rate-dependent) elastoplastic (IEP) constitutive model. A total of 9 model parameters is required, and their values can be properly determined via conventional laboratory tests. The validity of the proposed IEP is demonstrated using experimental data for Osaka Bay clay under various stress paths and strain rates, namely, long-term creep, constant rate of strain loading, relaxation, and their combination. Comparison of the model predictions and experimental results demonstrates that the theory of isotach elastoplasticity can be successfully applied to capture the strain rate and time effects on the mechanical behaviour of Osaka Bay clay.