Experimental study on soil-water characteristic curve of expensive soil considering net normal stress

The expansive soil is a kind of special soil with swell-shrinking, fractured and over-consolidated properties. In engineering construction, the expansive soil is generally under unsaturated state and complex applied stress environment. It is practical to describe qualitatively and quantitatively the soil-water characteristic curve (SWCC) of the expansive soil under a certain stress state. Based on this, the SWCC of Nanyang expansive soil in Henan Province are measured under four different net normal stresses (0, 40, 99, 199 kPa) using the GEO-Experts high-type pressure plate apparatus for stress-dependent SWCC (SDSWCC-H). Furthermore, a proposed SWCC equation which can clearly consider the effect of the net normal stress is validated using the experimental data. The results suggest that: (1) Nanyang expansive soil presents bimodal SWCCs because of gap-graded soil; (2) The net normal stress can significantly affect moisture realease speed of soil in the matrix suction range from 10 to 100 kPa and also change the air-entry vaule of expansive soil; (3) The accuracy of the SWCC model based on measured data of bimodal SWCC for Nanyang expansive soil is verified with high fitting precision. The proposed SWCC model can well reflect the relationship between matrix suction and water retention capacity under constant net normal stress.