Effects of net stress and suction history on the small strain stiffness of a compacted clayey silt

An experimental study was carried out to investigate the effects of the mean net stress and suction history on the initial shear stiffness, Go, of a compacted clayey silt. Isotropic tests were performed using two suction controlled devices, a triaxial cell and a resonant column torsional shear (RCTS) cell, so as to investigate the volumetric behaviour of this material. As for saturated soils, one can expect to find a strong correlation among stress history, volumetric state, and Go. Initial shear stiffness was measured almost continuously along various isotropic stress paths, including compressions and drying–wetting single stages or cycles, by using the RCTS cell. The collected data demonstrate a strong dependency of Go on mean net stress (p-ua; ua = pore air pressure) and matric suction (ua—uw; ua = pore water pressure). Cycles of suction, in particular increasing suction beyond the past maximum value, induce significant accumulation of irreversible strains and increase of stiffness, confirming that Go is not univocally related to the stress state (p-ua, ua-uw).