A study on interface shear behaviour of soil nails from pullout and direct shear tests

Pullout and direct shear (DS) tests are most commonly used to measure the interface shear strength parameters required for soil–nail design. This paper investigates the effect of the surface roughness, and relative density (RD) and installation process on interface shear behaviour between the groutless soil nail and dry sand medium through laboratory pullout and DS interface tests. The test procedure and the interface shear results obtained from pullout tests are discussed and compared with that obtained from DS tests besides the existing literature. The study shows that in the pre-peak stage, the shear stress–displacement behaviour obtained from interface shear tests is similar to pullout tests and soil–soil DS tests. However, in the post-peak stage, the behaviour is similar to soil–soil DS tests but different from pullout tests. The interface shear stress behaviour of soil nail is significantly influenced by the installation process, RD of soil sample and surface roughness of the soil nail.