SIMULATING SOIL DEFORMATION USING A CRITICAL-STATE MODEL .1. LABORATORY TESTS

The paper examines the ability of a critical-state model to predict stresses and deformations of agricultural soil in a variety of laboratory shear and compression tests. The critical-state model used is a simple extension to the well-known Modified Cam Clay model. The extension provides a smoother transition from elastic to plastic behaviour and, amongst other things, introduces a capacity to model cyclic loading. The model is incorporated into a finite-element program. The model predictions are compared with: experimental observations of simple and direct shear tests with both constant normal stress and constant volume conditions; cyclic uniaxial compression tests; compaction tests in U-shaped and V-shaped boxes; and observations of some gross structural features caused by shear in direct-shear boxes. Predictions are made for both the compressing, strain-hardening and the expanding, strain-softening regimes of behaviour. In all cases the material properties for the model were obtained from tests other than those being used for the comparisons. The model predictions generally compare well with the various experimental results, although some numerical problems were encountered in strain-softening conditions. This demonstrates the versatility of the critical-state model for predicting fairly general stress and deformation conditions in unsaturated soils using only five material-property constants. It also demonstrates that common laboratory strength and compression tests are adequate to measure the material properties.