Hydro-mechanical Coupling and Microstructural Evolution Mechanism of Expansive Soil under the Full Suction Range

Dubo Wang^*Mengzi LiZhuoran Wang

• North China University of Water Conservancy and Electric Power, Zhengzhou, China

The engineering properties of expansive soils are significantly influenced and controlled by their hydraulic behaviour. The microstructural evolution mechanism plays a crucial role in the hydraulic behaviour of expansive soils. By combining the pressure plate, saturated salt solution–vapour equilibrium, and WP4C instrument methods, a soil–water characteristic curve (SWCC) for expansive soil at all suctions during drying–wetting cycles was obtained, and expansive soil hysteresis and volume changes were analysed. The expansive SWCC under the full suction range exhibits a hysteretic phenomenon, which is attributed mainly to the different microstructures of the samples along the wetting and drying paths. During the entire humidification process, the pores decrease by 0.39, whereas during the entire drying process, the pores increase by 0.30. During the dry–wet cycling process, irreversible plastic deformations occur, indicating a significant coupling effect between saturation and void ratio (specific volume) with changes in matric suction. The microfabric evolution for pores of expansive soil was obtained by MIP and SEM. The measured pore size distribution curves show two distinct peaks corresponding to the micropores and macropores. The boundary between the inter/ intra-aggregate pores is 0.2 μm. The intra-aggregate pore volume distribution is consistent at all suctions. During initial wetting, the dominant pore diameter decreases, and the macropores close. During intermediate wetting, the pore distribution remains relatively unchanged. During final wetting, the pore distribution changes, and aggregate expansion deformation and soil expansion occur. These results lay the foundation for establishing a hydraulic coupled soil–water characteristic model and constitutive model that accounts for the influence of the microstructure of expansive soil within the full suction range.