Expansive soil is a problematic unsaturated clayey soil with distinct characteristics of swelling and shrinking with the change in water content. The mechanical behavior of the expansive clay is strongly influenced by water content or soil suction. It is characterized by heavy overconsolidation and crevice. The deformation and strength features of expansive soil are extremely complex. In expansive soil areas, geologic disaster occurs in a high frequency, and may cause enormous losses in economy and human lives.

This project performs extensive research on expensive soil, including the strain characteristics of expansive soil (a national science fund)、compaction properties and swelling and shrinking deformation characteristics of expansive soil、engineering features of filled subgrade in expansive soil areas etc. The quantitative relationship among  expansive deformation、 initial moisture content (w₀) and density (ρ) is obtained based on the experimental results.

Based on the extensive triaxial test data with the soil suction controlled for unsaturated expansive soil, the concept and hyperbolic model of suction strength are established. The model is suitable for use，in which parameter is easily determined and convenient for engineering practices. Moreover，the feature　of expansive deformation during the course of wetting and drying cycles and its effect on moisture removal are analyzed. These research achievements are successfully applied in engineering practices, such as pre-prediction of expansive soil ditches、cracking　mechanism　study of expansive soil roadbed and　 road surface、filled technology and technological quality of expansive soil embankment etc.