Impact of multidirectional shaking on liquefaction potential of level sand deposits

Multidirectional shearing, as induced by multidirectional shaking, involves variations not only in shear magnitude but also in shear direction, and in general involves deformations non-coaxial with the stress. Experimental results on saturated sand specimens using a biaxial simple shear device suggest that loading involving changes of direction may introduce significant reduction in the liquefaction resistance of cohesionless soil. However, centrifuge test results indicate that biaxial shaking has only limited impact on the liquefaction potential of level sand deposits. From numerical analysis, using a fully coupled ground response procedure (SUMDES) incorporating a comprehensive constitutive model for sand, and a theoretical study on the basis of the theory of plasticity, it was found that the in situ k(0) condition, and the fact that the mobilised shear stress under earthquake tends to decrease as the excess pore pressure builds up, abate the effect of multidirectional shearing on level ground response.