Hydro-mechanical behavior of expansive soils with different dry densities over a wide suction range

Many civil engineering projects are related to hydro-mechanical behavior of unsaturated expansive soils over a wide suction range, which was investigated by imposing suctions on an expansive soil using the axis-translation technique and the vapor equilibrium technique with saturated salt solution in this paper. Water retention test results on compacted expansive soil show that void ratio keeps decreasing along with increasing the suction in an entire suction range (from 0 to about 1000 MPa), and the soil–water retention curves in terms of gravimetric water content versus suction relation are independent of the dry density or void ratio when the suction is higher than 250 kPa. Therefore, the mechanical tests on an unsaturated expansive soil with constant water content can be considered as that at constant suction when suction is higher than 250 kPa. The stress–strain behavior at different constant suctions in the entire suction range measured from triaxial shear tests under a constant net confining stress shows that the strength and stress–strain curve of specimens with higher suction are higher than those with lower suction and the higher the suction, the more dilative the specimens. The strain softening appears when the suction is higher than a specific value and the appearance of strain softening is related to the sliding surface. The tested compacted expansive soil with extremely high suctions (i.e., 38.0 and 368 MPa) shows distinct peak strength, strain-softening and dilative behavior.