Force-Displacement Characteristics of Helical Soil Nail under Monotonic Pullout Loading: Experimental and Theoretical Study

This study investigates the shear stress-displacement behavior of helical soil nails (HSN) under different overburden pressure and monotonic pullout loading. Two types of individual HSN (ribbed solid and hollow plain) and a group of nine ribbed solid shafts HSN installed with uniform spacing are experimentally investigated. The study also examines vertical stresses and axial stresses developed along with HSNs. Further, theoretical modeling of the obtained experimental stress-displacement behavior has also been carried out. The results depict mobilization of nonlinear stresses under monotonic pullout for both individual and group HSN. The stress-displacement behavior is vividly marked by a pre-peak and post-peak stage. Higher shear stress mobilization is found for solid HSN as compared to hollow ones. A close agreement with a low coefficient of variance between measured and predicted values for overburden pressure between 5 and 50 kPa depicts the efficacy of the developed theoretical model. The results of axial strain for both shaft types HSN reveal strain softening during post-peak, which diminishes in case of group behavior. It is concluded that truncated cone rupture failure during group behavior significantly governs the stress-displacement response majorly by bearing than interface shearing resistance of soil plugging in hollow shafts.