Abstract: During earthquakes, the shear wave can be simulated by the horizontal bidirectional shear stresses mutually coupled in magnitude and direction. To investigate the influence of cyclic shear stress ratio (SSR) and phase difference on dynamic characteristics of soft clay under bidirectional loading, 19 groups of undrained cyclic simple shear tests have been performed on typical Wenzhou soft clay by using multi-direction cyclic shear apparatus. The test results show that the threshold cyclic stress ratio SSRx,menkan for the typical Wenzhou soft clay under unidirection cyclic shear loading is 0.096 and the critical cyclic stress ratio SSRx,limit is 0.15. Under the bidirectional cyclic shear loading, the increase of cyclic number N and the improvement of SSR will promote the development of shear strain and pore pressure u. When SSR is slightly larger than SSRx,menkan, the increase of will decrease the development of and u. When SSR is between SSRx,menkan and SSRx,limit, shear strain and pore pressure u increase rapidly with the increase of . When SSR is larger than SSRx,limit, the effect of phase difference on the shear strain and pore pressure u can be ignored.

Key words: cyclic simple shear, horizontal bidirectional load, soft clay, deformation, pore pressure