Microstructural insight into the hysteretic water retention behavior of intact Mile expansive clay

Water retention behavior of clayey soils usually exhibits a hysteretic phenomenon, which can be attributed to the ink-bottle effect, different contact angle during wetting and drying process, entrapped air etc. For expansive soils, along the wetting and drying path, significant microstructure change is usually observed. The effect of microstructure change on the water retention hysteretic phenomenon was studied in this paper for an intact expansive clay from China, Mile clay. The soil water retention curve of Mile clay was obtained at the full suction range. The evolution of microstructure along wetting and drying path for Mile clay was characterized by pore sized distribution obtained from mercury intrusion porosimetry tests. Test results show that a strong hysteretic phenomenon was observed for suction ranging between 40 kPa and 15 MPa. This hysteretic phenomenon was mainly contributed to the different microstructure of specimens along wetting and drying paths with similar water ratio. For higher suction, as adsorption mechanism mainly contributed to the water retention properties, for specimens with similar water ratio, even with different maximum filled entrance pore sizes, the corresponding suction were similar with each other. For the lower suction, due to the completely drying historical state of specimens on the main wetting path, slightly different pore size distributions were observed for specimens on the main wetting and drying path with similar water ratio.