Optimization of soil nailing design considering three failure modes

Soil nailing is a reinforcing method using the shear strength of in-situ ground and the pullout resistance of soil nailing. In the current korean slope design standard, only the pullout failure and the shear failure are considered as the main design factors. However, in the slope of an actual construction site, multi-face excavation is executed rather than full face excavation, and face failure can therefore occur in each excavation step due to the decrease of confining pressure on the excavation face during the top-down excavation. Therefore, it is necessary to include face failure as the main design factor in the slope design. This study verifies theoretically the mechanical behavior of face failure as well as pullout failure and shear failure. The constrained conditions for each failure mode are defined, and the optimization of soil nailing design is proposed on this basis. The design variables considered for the three failure modes are the bonded length of nail, the number of nails, and the prestress. These three design variables are estimated from the optimization design procedure proposed in this study considering constrained conditions. As the optimization design procedure of soil nailing proposed in this paper considers not only the pullout and shear failures but also face failure, it could be a more satisfactory design procedure in the actual field.