Effect of Suction on the Shear Strength of Soil–Rock Interfaces

Failure mechanisms of slopes along the coastal ranges of south-eastern Brazil very often indicate shallow shear surfaces, occurring at the sharp contact between the soil and the intact rock. Recent events has cost the lives of more than 800 lives due to heavy rainfalls in a very short period, in areas with and without anthropic actions. Most of the geotechnical studies are related to the shear strength of the soil in both saturated and unsaturated state. However, there is a lack of knowledge in strength parameters along soil–rock contacts. The present work attempts to fill this gap by the determination of shear strength parameters along sharp soil–rock contacts under saturated and unsaturated conditions. The present work focuses on small scale of roughness, which can be reproduced in laboratory experiments. In order to simulate these conditions, shear box tests were performed, using different interface conditions of roughness with specimens at different soil suctions. The results allowed the evaluation of the effect of roughness at the interface and soil suction on the cohesion, and friction angle, In particular, the behaviour of cohesion with variation in the degree of saturation and suction.