Generalized simple model for predicting the modulus degradation and strain accumulation of clay subject to long-term undrained cyclic loading

Abstract

Modulus degradations and strain accumulations of clays under repeated environmental loads are important factors in the design of offshore foundations. In this study, a simple model is proposed for predicting the modulus degradation and strain accumulation of clays subject to long-term cyclic loading. The development of the proposed model is based on a comprehensive database, including a series of undrained cyclic triaxial tests on the reconstituted kaolin clays. The concept of fatigue failure under cyclic loading is adopted to develop the model. Several influence factors, such as the initial stress ratio, initial confining stress, and overconsolidation ratio, are considered in the prediction model. The main feature of the proposed model is to predict the modulus degradation and strain accumulation simultaneously. This process is typically achieved separately by different models. At the isotropic condition or the symmetric (two-way) loading condition, the model tends to predict the modulus degradation. At the anisotropic condition or the asymmetric (one-way) loading condition, the model tends to predict the strain accumulation. The model predicts the modulus degradation and strain accumulation at the intermedium conditions defined by the initial stress ratio. This physical-based model can be easily calibrated with new test results or extended with additional influence factors (e.g., loading frequency).