A new method for the definition and measurement of roughness of soil-structure interface was proposed based on reversing the roughness measured by sand filling method.The new method, sand filling method and the method for the measurement of peak-valley distance were used to measure the roughness of the surfaces with semi-circle grooves made by the test and the surface with tooth grooves made by the other research scholars.The comparisons were made according to the results of measurement.The direct shear tests on the interface of red clay-concrete block were carried out using the large-scale direct apparatus.The effects of roughness on the interface characteristics of shear failure and deformation were studied by quantitative analysis and the effect mechanism of roughness were discussed.The results indicated that, for the measurement of roughness of interface,the new method suggested by this paper is more effective than both sand filling method and the method for the measurement of peak-valley distance.The shear failure of interface agrees well with the Mohr-Coulomb strength failure criterion.The roughness has little effects on the internal friction angle.The growth rates of the shear strength and the cohesion reduce with the increment of roughness of interface.With the increment of roughness of interface, the cohesion of interface increases until it approaches to the cohesion of red clay.If the cohesion of interface approaches to that of red clay,the shear failure may occur on the interface or in the soil near the interface.With the increment of the normal stress,the critical roughness decreases,meanwhile,the effects of roughness on shear strength of interface reduce.When the roughness of interface is low, the stress-dropping phenomenon is shown after the shear failure occurs.
