Comparison of interface shear strength of soil nails measured by both direct shear box tests and pullout tests

The shear stress-displacement behavior and ultimate shear strength at the interface between the cement-grout nail and surrounding soil are of practical importance in the design and safety assessment of a soil nail system. The most commonly adopted method to measure the interface shear strength of a soil nail is a pullout testing method. The current study attempts to investigate the interface shear behavior between the cement-grouted materials (soil nails) and a completely decomposed granite soil using both a large-size direct shear test apparatus and a laboratory pullout test apparatus. The laboratory testing procedures are briefly described. The main test results obtained are presented, followed by discussion on the shear behavior of the soil-grout interface. The interface shear behavior measured from both the interface shear tests and the pullout tests on the same soil tested in the same or a similar condition are compared and discussed. It is shown that the shear stress-displacement behavior of the soil-grout interface in the interface shear tests is similar to that of the soil-soil tests, but is different from the behavior in the pullout tests. Journal of Geotechnical and Geoenvironmental Engineering