Undrained Cyclic Shear Behaviour Of Clay With Initial Static Shear Stress

Abstract

A series of undrained cyclic triaxial compression tests has been performed on a high plastic marine clay. Testing was performed for not only isotropically but also anisotropically consolidated specimens under various combinations of initial static and subsequent cyclic shear stresses. The cyclic shear strength was first discussed, and then, residual shear strain was investigated related with effective stress ratio at the peak of cyclic stress. Based on the experimental results, a semi-empirical model was proposed for evaluating the development of residual shear strain during cyclic loading. The model successfully explained the behaviour of clay subjected to various magnitude of initial static and subsequent cyclic shear stresses. INTRODUCTION The main interest about the design problem against earthquake has been focused on liquefaction of saturated sands. Clays have been considered to be rather stable than sands during earthquake. However, serious damages of structures based on thick clay layers were reported in 1985 Mexico Earthquake (Seed et al. [6] , Mendoza et al. [2] ). A large deformation of ground due to amplification of seismic motion is recognized as a characteristic of clay behaviour during earthquake. Additionally, a lot of collapses of fills were caused by failure of clay base layers in 1964 Niigata Earthquake, 1978 Miyagiken-oki Earthquake and 1983 Nihonkai-chubu Earthquake in Japan. On the other hand, in the design of offshore platform against wave loading, the cyclic properties of clays have been investigated and taken in the practical design method (Andersen et al. [1] ). Although the Transactions on the Built Environment vol 3, © 1993 WIT Press, www.witpress.com, ISSN 1743-3509