A bounding surface model for unsaturated compacted bentonite

Abstract

This paper presents a bounding surface model for unsaturated compacted bentonite based on the critical state theory and bounding surface plasticity. In the proposed model, a shear bounding surface was proposed for describing shear behaviour. A new loading collapse curve was defined to describe suction effects on the yield behaviour. Meanwhile, wetting and drying bounding surfaces were proposed to represent the swelling and shrinkage volume change induced by suction changes. Furthermore, isotropic hardening rule was incorporated into the bounding surface formulation with an associated flow rule. Finally, a simplified form of plastic modulus was introduced to describe elastoplastic behaviour within the bounding surface and the Hvorslev surface was employed to describe the peak strength of heavily compacted bentonite. The proposed model has great potential to realistically describe some features of compacted bentonite including strain hardening or strain softening; monotonic loading under isotropic or one-dimensional compression; yield behaviour due to suction; swelling behaviour induced by changes of suction, etc. With the proposed model, simulations were performed on results of oedometer tests conducted under different suctions, triaxial compression tests and swelling potential tests. Validation showed that good agreements were reached between simulations and the experimental results. Highlights A loading collapse bounding surface was proposed to describe the influence of initial dry density on yield stress A shear bounding surface was proposed for describing hardening or softening behaviour The Hvorslev surface was introduced to reflect the peak strength and the water content effect on the peak strength Wetting–drying bounding surface was proposed for describing the volume change induced by suction changes