Prediction of excess pore water pressure and post-cyclic settlement on soft clay induced by uni-directional and multi-directional cyclic shears as a function of strain path parameters

The effects of cyclic shear direction, shear strain amplitude and number of cycles on the accumulation of excess pore water pressure and on the recompression were investigated for a cohesive soil by using the multi-directional cyclic simple shear test apparatus in which the uniform or irregular cyclic shear strain was applied to the specimen from two perpendicular directions in the horizontal plane. It is shown that at the same shear strain amplitude and number of cycles, excess pore water pressure and post-cyclic settlement induced by multi-directional cyclic shear are larger than those generated by uni-directional one. For multi-directional cases, these parameters increase with the phase difference. The unique relations of the excess pore water pressure ratio and the post-cyclic settlement versus cumulative shear strain are obtained for uni-directional and multi-directional cyclic shears and also for multi-directional cyclic shear with various phase differences, and these results lead the effect of cyclic shear direction to be negligible. Furthermore, an estimation method of excess pore water pressure ratio and post-cyclic settlement is presented and the validity of this method is confirmed for both uniform and irregular cyclic shears.