Physical and Mechanical Behaviors of Compacted Soils under Hydraulic Loading of Wetting–Drying Cycles

Abstract

Exposed geo−infrastructures filled with compacted soils experience cyclic wetting–drying effects due to environment and underground water fluctuations. Soil physical and mechanical behaviors are prone to deterioration to a great extent, e.g., swelling, collapse, or even slope failure, resulting in huge losses to human life, safety, and engineering construction. In this paper, hydraulic loading tests of wetting–drying cycles were carried out on compacted fine soil via a one−dimensional pressure plate apparatus equipped with bender elements. The influences of wetting–drying paths on the soil characteristics of moisture content, void ratio and shear modulus were obtained and analyzed. Results showed that cyclic wetting–drying effects weakened the soil’s water retention capacity. It was observed that it was harder for pore water to approach saturation at a lower matric suction level and to be expelled at a higher matric suction level. Typical swelling and shrinkage deformations occurred during the hydraulic loading processes, and volume expansion was generated after the drying–wetting cycles at a given value of matric suction, which deteriorated the densely compacted soils to a relatively looser state. Then, a unified soil–water characteristic surface was proposed to describe the unique relationships of moisture content, void ratio, and matric suction. Moreover, the small−strain shear modulus of the soil, in terms of shear wave velocity, was reduced by 32.2–35.5% and 13.8–25.8% at the same degree of saturation during the first and second wetting paths, respectively. Therefore, the volume expansion and modulus degradation resulting from the wetting–drying cycles should attract particular attention to avoid further distresses in the practical engineering.