Comparison of Interface Shear Strength of Soil Nails Measured by Both Direct Shear Box Tests and Pullout Tests

Abstract

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.