Abstract

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.

Introduction

For infrastructural developments in congested urban areas, it is often necessary to excavate soils either vertically or with steep slopes that may not have an adequate factor of safety (FS). Soil nailing is a very common technique that is generally adopted for such slopes so that the FS is increased to the desired level. In recent years, soil nailing has gained momentum all over the world as a preferred, popular, and cost-effective method for construction of such steep-cut slopes and also in the in situ stabilization of natural slopes. The construction process of soil nailing and installation of the nails is extremely flexible and allows for adjustment of nail directions to maximize the reinforcing action. Soil nailing can be effectively implemented in natural cohesive materials, such as silty clays, low-plasticity clays, and naturally cemented sand/gravel deposits. It is not recommended for sands and gravel without cohesion, organic clays, or expansive and swelling soils (Lazarte et al. 2003).