Soil-water retention of 9 kinds of soils under high suctions

The soil-water retention curve (SWRC) is the important constitutive relation of unsaturated soil. Most SWRCs are determined by the axis translation method which is suitable for suctions in the range of 0 to 1.5 MPa. However, the relative humidity is usually less than 95 % in engineering practice, which means suctions larger than 7.1 MPa. For this reason, the SWRCs for adsorption (wetting) and desorption (drying) of Wyoming bentonite, Ningming expansive soil, Jingmen yellowish-brown expansive soil, Denver claystone, Jingmen brown expansive soil, Wuhan clay, Sanmenxia silty clay, Zhengzhou silt and Kaifeng sand are determined by the dynamic dewpoint isotherm method under the relative humidity in the range of 3 % to 95 % (for suctions in the range of 7.1 to 482.9 MPa). w₉₅ (gravimetric water content under relative humidity of 95%) is adopted to quantify the soil-water retention capacity. HHA (hydraulic hysteresis area between adsorption branch and desorption branch of SWRCs) is adopted to quantify the magnitude of hydraulic hysteresis. Δw_max (the maximum value of the difference of gravimetric water content between adsorption branch and desorption branch of SWRCs under the same suction) is adopted to quantify the deviation of gravimetric water content caused by hydraulic hysteresis. The quantitative relationships among w₉₅, HHA, Δw_max and liquid limit, plastic index, cation exchange capacity and specific surface area are constituted. w₉₅ is proposed as the criterion for the classification of expansive soils, and its feasibility is verified. The Fredlund and Xing (1994) equation is modified to simulate the adsorption and desorption branches of SWRCs of the above 9 kinds of soils under high suctions satisfactorily.