Experimental Investigation and Modeling of Pullout Response of Soil Nails in Cohesionless Medium

Soil nailing is a popular in situ reinforcement technique that is widely used to stabilize unstable slopes and vertical faces of excavations and tunnels. The pullout capacity of soil nails is a governing design parameter for the soil-nailing technique. Therefore, the determination of accurate pullout capacity is necessary to ensure adequate internal stability of the stabilized structures. The article presents a laboratory investigation on the pullout force-displacement behavior of the soil nails installed in a dry, cohesionless medium. The study describes the effects of surface roughness, surcharge pressure, and relative density on the pullout response of soil nails. The results show that with an increase in the roughness, there was an increase of more than twofold in the mobilized maximum pullout resistance of the soil nails. Furthermore, the relative density was found to have a significant influence on the pullout capacity and the mobilized peak interface friction angle of the soil nails. The pullout force-displacement behavior of the smooth surface soil nail was found to be elastic-perfectly plastic in nature, whereas a strain-softening behavior was observed for the soil nails with a rough surface. The experimental data were used to formulate an empirical model (substantiated by the previously published data) that can predict the peak and residual shear strength of the nail-soil interface at different combinations of surface roughness and surcharge pressure. The proposed empirical model was then incorporated into the existing constitutive models to reproduce the observed (experimentally) pre and postpeak pullout force-displacement response of the soil nails. The simulated results are in good agreement with the experimental observations.