Compression Response of Sedimented Unsaturated Soils

Abstract

This paper presents an experimental study on the hydromechanical 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, and 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.