Direct shear testing study of the interface behavior between steel plate and compacted completely decomposed granite under different vertical stresses and suctions

In this paper, the shearing behavior of soil-steel interfaces sheared at different planes is examined using a modified suction- controlled direct shear apparatus (MDSA). Direct shear tests on soil-steel interfaces sheared at three shear planes at three different suction values were conducted. Test results show that matric suction has a significant influence on interface shear behavior and shear strength and that the critical (or minimum) interface shear strength depends on the applied matric suction. Net normal stress affects both peak and postpeak shear stresses of the interfaces and those of the pure soil. The suction envelope for the interfaces is nonlinear. The interface shear strength values from experimental results are compared with the values predicted from an existing analytical model that considers the influence of soil dilation. The results indicate that the analytical model is suitable for predicting the unsaturated interface shear strength of rough soil-steel.