Finite element modeling soil nail pullout behavior and effects of overburden pressure and dilation

Grouted soil nails are widely used in the slope stabilization projects. It is of great interests to engineers and researchers to study the mechanism of the soil nail pullout resistance under different conditions. In this paper, a three-dimensional (3D) finite element (FE) model is developed to simulate the behavior of soil nail considering the effects of overburden pressure and dilation. The Mohr-Coulomb model is adopted to simulate the soil behavior. The interaction between the soil nail surface and the surrounding soil is modeled by Coulomb model. Contact pairs are used at the soil-nail interface so that the sliding failure can be considered during the pullout analysis. The model parameters are calibrated by the triaxial soil test data. It is found that the selected model can represent the soil stress-strain behaviour under different confining pressures. Large scale laboratory pullout test data are used to compare with the modelling results and verify the model. The soil stress variations surrounding the soil nail before and during pullout are demonstrated in FE modelling. Parametric analysis is carried out to investigate the effects of soil dilation and overburden pressure on the soil nail pullout resistance. It is found that the effect of interface soil dilation under small overburden pressures is not so significant as that under OP = 200 kPa and 300 kPa.