Effect of unloading on shear behavior of interface between sand and concrete

A total of 36 groups of direct shear tests to samples with the sand-concrete interface were conducted under three different initial normal stresses and three roughness values of interface to analyze the mechanical properties of the interface and the effects of the unloading ratio and roughness on its softening and shear dilation. The soil for test is the gray silt in ③2 layer from Shanghai. The test results show that the initial normal stress influences indirectly the peak shear stress of interface by affecting the density and moisture content of the soil at interface. The peak and residual shear stress of interface decrease linearly with the increasing of the unloading ratio. The roughness of interface has no significant effects on the decreasing rate of peak and residual shear stress varied with the unloading ratio. The residual shear stress of interface increases gradually with the increasing of roughness and tends to reach the same value as the applied normal stress when specimens were sheared. The softening phenomenon of the interface becomes more obvious with the increasing of the unloading ratio. There exists a critical value for the roughness r of interface,i.e.,the softening of the interface is little affected by the roughness when r<10 mm and is affected by the roughness when r>10 mm. The shear contraction of interface appears under the loading conditions,and the shear dilation of interface transforms gradually to the shear contraction as the unloading degree decreases. The maximum value of shear dilation of interface increases with the increasing of unloading degree,whereas the maximum value of shear contraction decreases under the same roughness of interface. © 2018, Science Press. All right reserved.