Selected topics in numerical simulation of supported excavations

This paper describes factors that affect the selection of the type of finite element formulation, the initial stress conditions with emphasis on urban environments, the importance a faithful representation of the construction process, and factors affecting the selection of the constitutive model. To illustrate the importance of small strain non-linearity, responses measured in laboratory specimens cut from hand-carved block samples of soft to medium clay obtained from an excavation in Chicago are summarized. To model these responses, a tangential stiffness model is described and used to represent the constitutive relationship of the clays in a finite element simulation of an instrumented tied-back excavation. The results of these simulations and those made assuming responses modeled by a Mohr-coulomb plasticity-based model are compared to observed results to illustrate the differences in the capabilities of the two types of constitutive models.