A Simplified Model Describing the Cyclic Behavior of Lightly Overconsolidated Clays in Simple Shear

The geological profile of submerged slopes of the continental shelf typically consists of normally to lightly overconsolidated clays with depths ranging from a few meters to a few hundred meters and very low slope angles. The stability of these slopes is often investigated with pseudo-static methods by reducing the dynamic loading to an equivalent inertial force. The simplifications are such that the analyses are seldom satisfactory in addressing the questions of amount of permanent displacement, time and strain rate effects and potential triggering effects. This report describes the formulation of a new simplified effective stress based model, which is able to capture the cyclic behavior of lightly overconsolidated soils. The model only describes a simplified-but realisticstress state in which only the stress normal to the slope plane and the shear stress in the slope plane are considered. The constitutive laws incorporates anisotropic hardening and bounding surface principles to allow the user to simulate different shear strain and stress reversal histories as well as provide realistic descriptions of the accumulation of plastic shear strains and excess pore pressures during successive loading cycles. The model parameters can be determined from standard DSS tests. Model performance is evaluated by comparing model predictions with measured response in cyclic DSS tests for Boston Blue Clay. For a given slope, the static (or permanent) shear stress acting in the direction of the slope can be modeled by performing Kα -DSS tests in the laboratory. The effect of consolidation stress history (i.e., Kα effects) on the measured soil response is evaluated by comparing monotonic and cyclic response of normally consolidated clays in simple shear.