Three-Dimensional Limit-Equilibrium Stability Analyses of Slopes and Effect of Inclusion of Soil Nails

This study undertook stability analysis of nailed soil slopes using the limit-equilibrium method (LEM) and considering a three-dimensional (3D) rigid-body rotational failure mechanism with the assumed slip surface being a part of a sphere. The moment equilibrium of the 3D wedge formed by the slope surface and the slip surface along with the nails embedded in it were analyzed as a whole. A specific-purpose computer code was written for factor-of-safety (FS) computation; the developed computer code is capable of analyzing an unreinforced slope and a nailed slope. The critical slip surface and the corresponding minimum FS value of the unreinforced slope were initially determined, taking into account all possibilities of failure (base failure, slope failure, and toe failure). For the critical slip surface so obtained, nails were then introduced at desired positions, and the FS value for the nailed slope was then estimated with the developed procedure. The developed method and computer code were verified by comparing the FS values of some benchmark problems [two-dimensional (2D) and 3D] obtained by the proposed method with those reported in the literature. The critical slip surfaces obtained from the proposed method were also compared with some of the benchmark problems. A parametric study was conducted to determine the effects of the inclination and spacing of the nails on the FS values.