Effects of the soil water content and relative roughness on the shear strength of silt and steel plate interface

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Using a self-developed large-scale direct shear apparatus, 72 series of tests on the interface of a silt-steel structure and 18 series of direct shear tests of silt were performed. The effects of the water content of soil, interface roughness and normal stress on the shear mechanical behavior of silt-steel structure interface were studied. The test results confirm that the water content obviously affects the hardening–softening behavior of the silt-structure interface. The curve of the shear stress with shear displacement of the silt-steel interface was similar to the trend of the direct shear test results of the silt. The shear strength of the rough interface (Rmax > 0 mm) was significantly greater than the results of the direct shear test of silt, and the shear strength of the smooth interface (Rmax = 0 mm) was less than the shear strength of the direct shear of silt. In the process of the interface shear test, the deformation of the soil body gradually increased with the decrease in soil water content and increase in interface roughness. The contribution of matric suction of unsaturated silt to the interface peak shear stress was more prominent and hardly affected the residual shear stress. The interface shear strength for unsaturated soil was modeled. The comparison between model results and experimental results shows that the calculation model can accurately predict the shear strength of the unsaturated silt-steel interface under different interface roughness conditions.