Abstract：A comparative laboratory study is presented on the physical and mechanical indexes，strength changes of intact samples during the process of dehydration，strength changes of compacted samples after saturating，as well as the dehydration and humidity absorption capability for the red clay in Guigang，Guangxi，and weak-expansive soil and mid-expansive soil in Jingmen，Hubei. The results show that the strength of the three kinds of soils possesses different rules during the process of dehydration due to the double effects of matrix suction and fissure. Because of the different swelling properties of red clay and expansive soil，the water contents of compacted samples corresponding to the maximum of dry density and CBR after saturation are higher in different extents than those corresponding to the optimum water content. The properties of dehydration and humidity absorption of tested soils are different due to the difference in mineral compositions. Even though there are some similarities between red clay and expansive soil on the physical and mechanical indexes，but the mechanical behaviors and water-sensitivity of these two special soils are obviously different. Hence，enough attention should be paid to these problems in the practical engineering projects.
