Liquefaction and cyclic failure of sand under bidirectional cyclic loading

Samples of saturated loose sand were tested under bi-directional cyclic loading to characterize liquefaction and cyclic failure, by using an advanced soil static and dynamic universal triaxial and torsional shear apparatus. Tests were performed with two cyclic components involving the horizontal shear stress (torsional shear stress) and the vertical shear stress (stress difference between vertical normal stress and horizontal normal stress) to provide an approximate presentation of wave or seismic loading conditions. Samples were consolidated under various initial static horizontal shear stresses and subsequently subjected to a specified level of dynamic loading. Three stress levels of dynamic load were concerned. Results show that the developed pore water pressure decreases linearly as initial static horizontal shear stress increases and decreases exponentially as consolidation stress ratio increases. An Empirical equation is obtained to express the relationship between the pore water pressure and the initial static horizontal shear stress (or consolidation stress ratio). For highly enough anisotropically consolidated test, the generated pore water pressure may be below zero. The cyclic loading resistance closely depends on whether there is negative pore water pressure occurring or not. Various deformation behaviors are shown for various consolidation conditions, and also for different dynamic loading conditions. It is attributed to the differences in the degree of shear stress reversal. © 2008 ejge.