Abstract: The characteristics of interface between the extrusion-sidewall and slab face of CFRD were investigated by carrying out a series of large scale shear tests of the interface with different surface treatment on the extrusion-sidewall.The relationship between the shear stress and the strain of the interface was analyzed considering the influence of treatment.It was shown that the friction between the extrusion-sidewall and the concrete slab decreased if filling materials were used in the tests.The effect of friction reduction was similar if mixture of emulsified asphalt and sand,or emulsified asphalt and PE membrane,was used while the effect of asphalt felt was more significant.Strain softening occurred when the PE membrane was used as interface filling materials,while it did not occur with the other filling materials or without filling materials.The Clough-Duncan model was capable of simulating the starting of the stress-strain relationship but it deviated a little with the test results when the shear stress was close to its peak.A modified ideal elasto-plastic model was suggested to characterize the stress-strain relationship of the interface with fewer parameters and a good coincidence.