A nonlinear Hvorslev surface for highly overconsolidated soils: elastoplastic and hypoplastic implementations

The clayfills are being produced in open-pit mining. The stress state in the stiff lumps of the clayfills is significantly lower than in situ level. As a result, their current states lie on the dry side of the critical state. The linear Hvorslev surface is widely used due to its simplicity and capability to model the limit stress condition of soils on the dry side. However, it may overestimate the strength at very low stress level. For this purpose, a series of drained triaxial tests were performed on a silty clay at very small stress levels. The failure points of the tested soil confirm a nonlinear relationship in p'-q plane on the dry side of the critical state. The degree of nonlinearity increases after being normalized by the Hvorslev equivalent pressure, which can be well modeled by a nonlinear power law criterion proposed by Atkinson (Geotechnique 57(2):127-135, 2007). Based on the test data and the critical state concept, a new failure line is proposed with help of the equivalent Hvorslev pressure. The nonlinear Hvorslev surface is then incorporated into an elastoplastic model and a hypoplastic model. Comparisons between the experimental data and simulations reveal that the proposed models can well represent the behavior observed in the laboratory.