Strain Rate and Preshear Effects in Cyclic Resistance of Soft Clay

Abstract

Cyclic constant-volume direct simple shear tests were performed on intact specimens of a sensitive clay reconsolidated to the in-situ stress state resulting in an overconsolidation ratio (OCR) of 2.2. The tests were conducted for different values of initial static undrained shear stress. The results confirmed that the high strain rate associated with cyclic loading has a significant effect on the cyclic resistance of soft clays. For up to 12 cycles, the strain-rate effect fully compensates the degradation of shear strength associated with cycling. The presence of an initial static shear stress decreases the cyclic resistance but increases the total undrained shear resistance, due to the partial or total disappearance of stress and strain reversal. The results indicate that for such a clay, the static undrained shear strength provides a conservative estimate in a pseudostatic analysis.