Abstract
The frictional behaviours between unsaturated soils and structure are controlled mainly by the complex phenomena that develop within a thin soil layer close to the contact area. The constitutive model for soil-structure interfaces (SSI) must be established to predict the performance of related soil-structuresystems accurately. Multi-stage suction-controlled ring shear (RS) tests with three different upper annular platens were carried out on an equal number of statically compacted samples of Shanghai clay under controlled suction states for a given net normal stress. A state dependent constitutive model for unsaturated soil-structure interfaces based on critical state concept considering bonding effect was proposed. In all stress conditions, the tested and predicted results for smooth interface and rough interface are well matched.