Abstract

The limit equilibrium method LEM is widely used for static and pseudo-static soil nailing designs. Soil nailed wall stability is usually evaluated based on a global factor of safety FSG under a predefined failure mechanism. When appropriate failure surfaces are adopted, FSG should reduce with the soil nailed wall inclination beta for different nail geometries (length L, inclination a and diameter D), soil-nail strength r(s), soil cohesion c' and angle of friction phi'. However, nail spacing S can change this trend since FSG increases with beta under certain combinations of beta and S. In this study the nail spacing effect has been evaluated using LEM assuming a bilinear failure surface with two rigid blocks and the Morgenstern-Price method where the failure surface is neither linear nor circular. However, it was found that FSG increases with beta for S 2.00 m, which can lead to potentially unsafe designs. Alternatively, the finite element method FEM was chosen including the strength reduction factor SRF methodology which is equivalent to FSG under failure conditions. It was found that results from FEM represent a significant improvement respect to those from LEM because curves in a FSG-p-s plot follow a logical trend as with the other parameters (L, alpha, D, r(s), c' and phi'). Finally, it is recommended to choose FEM instead of LEM in soil nailing designs. In case of using LEM, results should be carefully assessed, in particular for steep walls and close nail spacing.