Shear strength of overconsolidated clay for repeats of pore water pressure loading

This paper represents the change in shear strength of clay for repetitive pore water pressure loading with the use of both experimental tests and model simulation. Pore water pressure was increased under constant deviator stress to simulate the soil behavior in landslide. Yield stress in pore water pressure was obtained constant for repeats of pore water pressure loading, but failure stress was obtained to decrease. Failure stresses constituted the failure envelopment line in void ratio and effective mean stress space. This exhibits the process of change in both shear strength and state variable of soil caused by repetitive failures during pore water pressure loading cycles. In pore water pressure loading, the strain softening of clay develops due to dilation and the shear strength decreases. On the contrary, the shear strength recovery develops by consolidation effect in unloading. Failure stress varies due to two opposite effects of pore water pressure loading cycle. It was found the failure stress in pore water pressure approached to the balanced one between two opposite effects in repetitive pore water pressure loading cycles.