Abstract: Large-scale and medium-scale test equipments for impermeability characteristics of junctional zone between soil and hard surface are developed. The mutually orthogonal compressive stress, shear deformation and hydraulic gradient of the junctional zone between the soil and the rigid surface are controllable independently. The maximum shear deformation is greater than 1 m. The experimental studies on a compacted natural broadly graded clayey soil are carried out. The variation law of the permeability coefficient of the samples is discovered, that the permeability coefficient decreases gradually and then becomes stable after the sudden increase along with the start of the shear deformation. The history of shear deformation may weaken the phenomenon of the sudden increase of the permeability coefficient after the start of shear deformation. The permeability coefficient of soil samples with higher initial density, higher stress and larger external size is lower. Based on the corresponding relationship between the ratio of water conductivity coefficient of the junctional zone to its initial value and the ratio of permeability coefficient of the sample to its initial value, the possible thickness of the junctional zone considered to be between 0.075 mm and 1.0 mm is analyzed when the peak value of permeability coefficient is achieved. A revised model for clay particle clusters with irregular shape is proposed. The continuous change mechanism of permeability during shear deformation can be explained by fabric adjustment. The conjecture of the thickness of the junctional zone is also supported.