Compacted expansive clay is widely used as impermeable material of liner in the garbage landfill and prevention fill of nuclear waste material treatment. The permeability characteristics of expansive clay will effect on anti-seepage effect of liner cushion clay. Due to the difficulty of measuring permeability coefficient directly

the parameter is also evaluated by indirect method which is hard to truly explain permeability characteristics of unsaturated soil and phenomenon of migration of water. This paper discusses measuring permeability coefficient directly by GDS system and quantitatively analyses the influence of structure by permeability test and the SEM test which show the micro and macro-structure characteristics in the permeability process. The results show that the volume deformation of unsaturated expansive soil in permeation process is due to pore air is compressed and changes in pore structure. The pore water permeability coefficient of unsaturated expansive soil is controlled by suction

cell pressure

dry density and degree of saturation of soil samples.