Hydromechanical characteristics and microstructure of unsaturated loess under high suction

The water retention characteristics of intact and remolded loess in full suction range were tested by combining pressure plate apparatus and vapor equilibrium method. The shear tests of intact and remolded loess under high suction were carried out by the unsaturated triaxial apparatus. At the same time, scanning electron microscope (SEM) and mercury injection apparatus (MIP) were used to conduct microscopic tests to investigate the influence of structural differences on the hydromechanical behavior of unsaturated loess. The test results show that with the increase of suction the degree of saturation and water content of intact and remolded loess decrease, and the void ratio decreases slightly as well. Since the initial void ratio of intact and remolded loess is almost the same, the total mercury intrusion volume of their mercury intrusion tests is close. The pore structure morphology and dominant pore size range of intact and remolded loess obtained from SEM and MIP tests are different, and the structural properties vary, resulting in different soil-water characteristic curve in different suction ranges. The stress-strain relationship of intact and remolded loess mostly displays softening, and the remolded loess with a suction of 3.29 MPa shows hardening behavior. With the increase of suction, the cohesion and peak strength of both the intact and remolded loess increase significantly, and the volumetric deformation changes from shear shrinkage to dilatancy. Because the intact soil has certain structure and strong cementation, the increased magnitude of its cohesion will be greater than that of the remodeled soil, and the peak strength will be higher than that of the remodeled soil, while the internal friction angle is basically the same.