Cyclic and post-cyclic characteristics of marine silty clay under the multistage cycling-reconsolidation conditions

Abstract

Marine clay applied as the foundation of marine structures is constantly subjected to long-term cyclic loading, under which the drainage and reconsolidation of the clay are inevitable. However, in previous studies, the experimental method was to apply the completely undrained conditions. The clay's drainage effect during and after cyclic loading was considered in a few experimental studies, but the repeated effect of cycling and drainage which is a common condition for clay foundations in practical engineering was barely concerned. Therefore, a large number of triaxial tests were carried out considering the effects of confining pressure, cyclic stress ratio, degrees of reconsolidation, and the number of cycling-reconsolidation (C-R) cycles to clarify the cyclic and post-cyclic behavior of the marine silty clay. The test results show that the cyclic and post-cyclic characteristics of silty clay gradually stabilize after a given number of C-R cycles and are irrespective of continually increasing ones. The existence of residual cyclic pore pressure after the multistage C-R process can give rise to shear strength degradation. However, applying the C-R process can substantially enhance the clay's resistance to the shear, resulting in the lift of the post-cyclic shear strength. Besides, there is a consistent relationship between the post-cyclic shear strength and the reduction of water content caused by reconsolidation under different C-R conditions and a corresponding prediction formula has been obtained.