Hysteretic Shear Strength and Shear-induced Volume Change of Natural Expansive Soils Weathered from Shale

摘要

Two highly plastic expansive soils weathered from natural shale were investigated to determine shear strength and shear-induced volume change under a variety of hygroscopic and confinement conditions. The extents of suction and confinement were chosen such as to mirror the hydraulic and mechanical situations expansive soils experience in nature. During shearing, the soil sample with less swell potential showed volumetric dilation irrespective of suction level whereas the soil with higher swelling capacity displayed mostly contraction. The effects of initial structure, confining stress, suction, capillary history and strain level on shear strength and volume change were examined. The deviator stress increases with increasing suction, regardless of strain level and capillary history, because of the enhanced surface tension force. Capillary history impacts the peak shear strength of the flocculated sample because of significant structural evolution along the capillary paths while imposing little influence on the peak strength of the laminar sample. The large-strain shear strength, however, demonstrates little sensitivity to capillary history, regardless of soil type; because the specimens at this stage are more likely experiencing complete fabric destructuring and equilibrium of diffuse double layer repulsion.