An elastic-viscoplastic constitutive model for soil

The concepts of elasticity and viscoplasticity were used to develop an elastic-viscoplastic (EVP) constitutive model for soil. The mathematical description of viscoplastic straining includes a measure of both effective stress and the corresponding volumetric packing of the soil particles. The model is able capture the dependence of stress-strain relationships and undrained shear strength on strain rate, the development of irrecoverable plastic strains at constant stress, which is creep, and the relaxation of stresses at constant strain. A Newton-Raphson solution scheme with a stress point algorithm was used to implement the EVP soil model in a finite element program. The algorithms and assumptions required to implement the solution scheme are provided. Verification of the solution scheme is achieved by using it to analyze typical boundary value problems. A case history is developed for a geotextile reinforced highway embankment constructed on a soft estuarine deposit installed with prefabricated vertical drains. The EVP soil model was then used to simulate the measured deformation response. The numerical simulations closely matched the temporal changes in pore water pressures and surface settlement beneath the centerline and shoulder of the embankment. More importantly, the elastic-viscoplastic model simulated the pattern and the magnitudes of the lateral deformations beneath the toe of the embankment;... a notoriously difficult aspect of modelling the deformation response of soft soils. The simulations were achieved using a small set of material constants that can easily be obtained from standard laboratory tests. The research validates the use of the EVP model for problems involving heterogeneous soft soil deposits beneath loading from a geotechnical structure.