Static Liquefaction Analysis Considering Principal Stress Directions and Anisotropy
Static liquefaction failure of a sloping ground occurs when the shear stress applied by a monotonic triggering load exceeds the undrained yield (peak) shear strength of the saturated liquefiable cohesionless soil. Current practices for determining the in-situ undrained yield strength for ground subject to static shear stress either rely on a suite of costly laboratory tests on undisturbed field samples or empirical correlations based on in-situ penetration tests which do not account for the effects of anisotropic consolidation, intermediate principal stress, and mode of shear on the degree of strain softening and brittleness of cohesionless soils.
This study presents the effects of variations in the direction and relative magnitudes of principal stresses associated with different modes of shear and ground slopes on static liquefaction failure of cohesionless soils. Empirical relationships are shown between soil brittleness index and maximum excess pore water pressure ratio to characterize soil shearing behavior observed in a large database of undrained laboratory shear tests. The application of these relationships for estimating the static liquefaction triggering strength of cohesionless soils under sloping grounds is described for plane- strain boundary conditions and the results are compared with those back-calculated for several cases of static liquefaction flow failures.