Compression Response of Sedimented Unsaturated Soils

Abstract

This paper presents an experimental study on the hydro-mechanical behavior of unsaturated sedimented soil to understand the impacts of suction on the apparent yield stress and gain insight into the differences in behavior from compacted soils. A large-strain oedometer was developed for use in a triaxial cell that permits initial sedimentation of soils from a slurry under backpressure, suction control using the axis translation technique, and mechanical loading to characterize the compression curve. A flow pump was used to control the pore water pressure at the base of the soil specimen and to track water flow during suction application and mechanical loading. After initial consolidation of saturated soil specimens from a slurry, the specimens were unloaded, different suction values were applied, then the axial stress was increased to 11 MPa at a constant strain rate. An increase in apparent yield stress with suction was observed, and the compression curves for higher suctions diverged without reaching pressurized saturation in the applied stress range. When compared with compression curves for the same soil compacted dry of optimum presented in previous studies, the sedimented soil had a greater yield stress at saturated conditions but a similar increase in yield stress with suction. Sedimented soils also experienced smaller changes in void ratio with applied net stress and a higher air entry suction value compared to compacted soils, reflecting a more compact soil structure. Suction was found to have a greater impact on yield stress than suction stress for both sedimented and compacted soils.

Deformation and Strength of Unsaturated Loess—Hydraulic Coupling Effects under Loads

“…The undrained shearing of unsaturated soil essentially involves a constant water content shearing process. Although the volume reduction in the pore spaces within the soil during shearing does not change the water content [41], it does result in an elevation of saturation, as defined by the degree of saturation. The decrease in shear strength of the soil occurs due to the increase in saturation, despite the water content remaining constant.…”