Method for estimating system stiffness for excavation support walls

Excessive excavation-induced movements aremajor concerns formost underground construction projects in urban areas. Thesemovements can lead to significant damage in adjacent structures.When average to good workmanship is employed during the installation process of the excavation support systems, the consequent ground movements aremost influenced by the support system stiffness. Therefore, choosing themost appropriate stiffness for an excavation support system is crucial to minimizing excavation-related damage to adjacent buildings and utilities. This paper presents a semiempirical design methodology that facilitates the selecting of the excavation support systemstiffness in such a way that limits excavation-related ground movement. As part of the proposed design methodology, a new parameter was developed called the relative stiffness ratio. This new parameter relates the strength and stiffness of the soil with the stiffness of the excavation support system and was developed from a comprehensive parametric analysis that incorporated a fully three-dimensional finite-element analysis of a generalized excavation that realistically modeled the excavation geometry, excavation support system configuration, and excavation activities. The performance of the proposed methodology was evaluated using several excavation case histories reported worldwide. The results of the evaluation show that the new relativestiffness ratio performed well in predicting the support system bending stiffness and theactual excavation-induced lateral deformations of the case history support systems.