Response of Sands to Multidirectional Dynamic Loading in Centrifuge Tests

Abstract

Dynamic centrifuge tests were performed to investigate multidirectional loading effects on the shear and volumetric response of saturated sands under partially drained, level-ground conditions. These tests illustrate that dense sand shear response is not affected significantly by multidirectional shaking and can be estimated reasonably by one-dimensional nonlinear total and effective stress site response analyses. Multidirectionality factors for both excess porewater pressure (MDFru) and vertical strain (MDFεv) tended to increase with density and decrease with shaking intensity. Specifically, MDFru ranged from about 1 to 4, with an average value of about 2 for low ru values and MDFru approaching unity as the soil approaches liquefaction. Similarly, MDFεv ranged from about 1 to 3, with an average value of about 2 for low ru values and MDFεv approaching 1.3 as the soil approached liquefaction. Multidirectionality factors as functions of the factor of safety against liquefaction are proposed that differ from constant MDFs recommended elsewhere. Lastly, energy-based intensity measures provided nearly unique estimates of excess porewater pressure and vertical strain for both uni- and bidirectional motions, avoiding the need for MDFs.