Elastoplastic modelling of hydraulic and mechanical behaviour of unsaturated expansive soils

The Barcelona basic model (BBM) proposed by Alonso et al. cannot predict the mechanical behaviour of unsaturated expansive soils, and the Barcelona expansive model (BExM) for unsaturated expansive soils is complicated, and the micro parameters and the coupling function from micro-structural strain to macro-structural strain are difficult to be determined. This paper presents an elastoplastic constitutive model from the macroscopic view for predicting the hydraulic and mechanical behaviour of unsaturated expansive soils based on an existing hydro-mechanical model for unsaturated non-expansive soils. The model takes into consideration the coupled effects of the saturation degree and void ratio. The concept of equivalent void ratio curve (EVRC), which is different from the yield curve, is introduced in the model. The predictions are performed on the test results published in public, which include the swelling tests under constant net stresses, isotropic compression tests and triaxial shear tests under constant suctions. The comparisons between the measured and predicted results indicate that the proposed model can quantitatively predict the hydraulic and mechanical behaviour of unsaturated expansive soils.