Research of soil-water characteristic curve of expansive soil at Xiaoxiang Expressway

Expansive soil is a particular kind of clay that possesses potentials of swelling and shrinkage, crack and over-consolidation, which reduce the slope stability. Lasting rainfalls often induce landslides in shallow soil. Thus expansive soil slope is a hot topic achieving much attention. Soil-water characteristic curve (SWCC) was obtained from in-situ matrix suction and saturation degree measured with thermal conductivity sensors and moisture probes in a slope of expansive soil at Xiaoxiang Expressway in Hubei province, China. Air entry value (AEV) and residual saturation (RS) can be acquired from SWCC. Field SWCC can actually reflect the relationship between matrix suction and saturation, and offer necessary parameters that determine the strength caused only by suction. Relative permeability coefficient was derived from SWCC too. Through SWCC the slope stability factors under saturated and unsaturated conditions were calculated and compared according to Bishop’s method. Permeability coefficients under different water contents are obtained from SWCC. The results indicate that the slope stability of expansive soil is closely linked with SWCC, and that SWCC significantly simplifies calculation of unsaturated soil strength.