Analysis of Deep Excavation in Boston

Abstract

This paper describes the application of a finite‐element analysis for modeling the top‐down construction of a seven‐story, underground parking garage at Post Office Square in Boston. The analysis incorporates coupled flow and deformations within the soil for real‐time simulation of construction activities; a numerically accurate algorithm for excavation in nonlinear soil; and advanced constitutive modeling of clay behavior. Predictions are evaluated through comparisons with extensive field data, including wall deflections, soil deformations, surface settlements, and piezometric elevations. Differences between predicted and measured wall movements are attributed primarily to postconstruction shrinkage of the roof and floor system, while settlements are affected by unrealistic modeling of piezometric elevations in the underlying rock. A modified analysis, incorporating these factors, greatly improves agreement with the measured data. The results demonstrate that reliable and consistent predictions of soil deformations and ground‐water flow can be achieved by advanced methods of analysis without recourse to parametric iteration, but emphasizes the need for adequate characterization of engineering properties for the entire soil profile.