Cyclic and post-cyclic behaviour of soft clays

Abstract

In this study, the cyclic and post cyclic behaviour of reconstituted Singapore Upper Marine Clay and Kaolin Clay are examined through a series of two-way strain-controlled cyclic triaxial and resonant column tests. All triaxial tests are conducted using strain rates sufficiently slow for pore pressure equilibration within each specimen to facilitate reliable effective stress analyses. Results herein reveal that dilation of the clay structure occurs during cyclic loading once its stress ratio reaches 0.6 times the critical state parameter (M), defining the phase transformation line. As cyclic loading progresses, the cyclic oscillations in the effective stress and stiffness for both clay types resulted in distinctive ?butterfly? profile in their effective stress paths and their hysteretic stress-strain loops gradually collapse in size to form S-shapes. Such behaviour is analogous to that reported for dense sands under cyclic loading. Based on the experimental findings, a three-surface hardening model of the bounding surface type is proposed.