Abstract: The expansive soil in Panzhihua region was generated during the Pleistocene glacial period of the second late glacial period.Based on physical and mechanical tests and analysis of laboratory and field,this paper reveals the physical and mechanical properties of the expansive soil.The properties have a great dispersion and are related with many factors including soil mineral composition,moisture content,fracture surface,buried depth,gradation,test conditions.Experimental results show that the fracture surface of the expansive soil can be divided into two types with different smooth degrees.They are the types of smooth fracture surface and smooth surface scratches.Coarse-grained minerals have little effect on the expansion and shrinkage.But fine-grained minerals have a greater impact on the expansion and shrinkage.For exposed or near-surface soils,they have been weathered intensely,,developed more cracks,have larger expansion efforts.For the expansion soil from same site with higher montmorillonite content,it has a greater freedom of expansion,a higher level of expansion.The physical and mechanical property indices of the expansive soils from different sites have limited differences.The clay contents in the expansion soil is not significant.The shear strength values of the expansive soil from different sites can change greatly.The shear strength values of the expansive soil from the same site can have some fluctuations.A majority of the expansive soils are hard plastic to hard state.Their compressive deformation at natural state is small.Their bearing capacity at natural state can be doubly reduced when they are fully saturated.