In recent years, soil nailing has been widely used to stabilize excavated steep slopes. This method has gained world-wide acceptance in both theory and practice due to its economy, technical advantages and construction speed. Its design is often controlled by the allowable deformation level, especially when buildings and/or other underground facilities exist near the excavation. Limit equilibrium methods that are used for the analysis and design of nailed soil structures fail to give any information about deflections. Therefore, predictions of the deformation behavior of a soil-nailed structure through numerical methods such as FEM are required to ensure that displacement limits set by the construction requirements are not exceeded. Also, Federal Highway Administration (FHWA-2003) provides charts for estimating lateral displacements of soil nail walls. This paper is an attempt to investigate accuracy of numerical methods and FHWA charts for estimating displacements of soil nail walls. For this purpose, we studied six walls that were monitored by inclinometers or microgeodesy surveying and their displacements were measured. These walls are numerically modeled and displacement patterns are determined using the software PLAXIS for every step of the excavation. It is shown that the measured and calculated displacement patterns and their values are closely comparable but calculated displacements are smaller than measured displacements at the top of the walls. It is also shown for deep excavation with cohesionless granular soils, the estimation of lateral displacements as a certain percentage of excavation height according to FHWA charts lead to considerable underestimation of lateral displacements.
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