Cyclic Degradation and Pore-Water Pressure Response of High-Plasticity Compacted Clay

This experimental study focused on cyclic degradation and cyclic pore-water pressure response of high-plasticity compacted clay under different dynamic loading and initial static shear stress conditions. The strain-controlled undrained cyclic simple shear tests were performed at different initial static shear stress ratios (τs/Su=0, 0.45, 0.65, 0.79, and 0.87), cyclic strain amplitudes (γc=0.5%, 1.5%, 2.5%, and 3.75%), and frequencies (f=0.1, 0.5, 1, and 2 Hz). The results revealed that the initial static shear stress significantly increased the magnitude and rate of stiffness degradation and cyclic pore-water pressure generation. The mobilized shear stress under cyclic loading decreased below the static shear strength within only five loading cycles. The shear modulus increased and the damping ratio decreased with the increase in frequency and decrease in cyclic strain amplitude. The enhanced rate of stiffness degradation followed a power-law functional relationship with cyclic strain amplitude, and its trend was dependent on the magnitude of the initial static shear stress ratio and the cyclic strain-reversal conditions. The experimental results clearly demonstrated the coupling between cyclic degradation and pore-water pressure generation. A strain-based model was formulated for the risk assessment of compacted high-plasticity clay (CH soil) subjected to combined static and cyclic loading.