An effective stress based shear strength criterion for unsaturated compacted double-porosity clays

An effective stress based shear strength criterion is proposed taking into account the fundamental effects of microstructure characteristics on retention properties of compacted double-porosity clays and their overall coupled hydro-mechanical behaviour. Results of triaxial compression tests carried out on saturated and unsaturated samples of a compacted scaly clay show that points representative of failure conditions depict a unique failure envelope when the macropore degree of saturation is used in the definition of the effective stress and its evolution with the suction is taken into account. Furthermore, the proposed criterion is very effective to consider the most relevant aspects of suction influence on the shear strength of double porosity unsaturated soils.