Interface Behavior from Suction-Controlled Direct Shear Test on Completely Decomposed Granitic Soil and Steel Surfaces

Abstract

A soil-structure interface is defined as the contact surface between a soil and a structure through which stresses are transferred from the soil to the structure or vice versa. The ultimate shear strength at the interface is one of the key parameters required for the design and safety assessment of a structure in the soil, such as pile foundations, retaining walls, buried pipelines, and soil nails. In this paper, the shearing behavior of completely decomposed granite soil and steel interfaces is examined using a modified suction-controlled direct shear apparatus. A series of direct shear tests was performed on two different types of soil-steel interfaces under different stress state variables. The experimental results were used to investigate the influence of counterface roughness on the failure envelopes of soil-steel interfaces. Test results show that matric suction has a significant influence on the shear behavior and shear strength of the interfaces. It has been observed that the critical interface shear strength for a specific counterface roughness and net normal stress (NNS) depends on the applied matric suction. Also, both the peak and the postpeak shear stresses are greatly influenced by variation in NNS. Furthermore, the experimental shear strength data are compared with an analytical model that considers the influence of suction and dilation on an apparent interface friction angle. It is noted that, for the applied NNS and matric suction, the analytical model works well for both rough interfaces.