Suction effects on the pre-failure behaviour of a compacted clayey soil

This paper explores the pre-failure behaviour of a compacted clayey soil, when subjected to shearing (axial compression) under undrained conditions. Specifically, the study focuses on the effect of the Suction state on the undrained Young modulus. The experimental programme carried out in a control led-suction triaxial cell involved two stages. In the first stage, samples were left to equalise at specified matrix suctions using the axis translation technique. Afterwards, undrained axial compression tests with pore-water pressure and sample deformation measurements were run at a relatively low constant displacement rate to allow for suction equalisation throughout the sample. Axial stiffness could be related to the initial matrix suction before the shearing stage. In this way, the evolution of the undrained Young's modulus was tracked during shearing where different responses were observed. To the authors' knowledge, available information concerning this aspect of unsaturated soil is very limited in spite of its practical relevance.