Hydro-mechanical behaviour of sandy silt under generalised stress conditions

Abstract

This paper presents results on the deformation response of an artificially prepared sand-silt mixture in a hollow cylinder apparatus. The wetting stage was performed under constant mean net stress (p¿=200 kPa) and deviatoric stress (q=200 kPa) but at different intermediate principal stresses (controlled through the principal stress parameter b=(s2-s3)/(s1-s3) and with values b=0, 0.5 and 0.8). Shear strength tests were first performed at constant mean net stress, different Lode angles and water contents (as-compacted and saturated) to ensure that the aforementioned stress state could be applied at the as-compacted water content. Consistent shear strength results were obtained when compared to triaxial compression and extension results at different water contents, which allowed defining the variation of the critical state line with Lode angle and suction. The soaking results indicated that collapse under constant mean and deviatoric stresses was larger when the intermediate stress coincided with the minor one, i.e. under conventional axi-symetric triaxial compression state (b=0). This is a consequence of the dominant shear strains that occurred during saturation when the stress point reached the critical state line at b=0.5 and 0.8.