Analysis of Deep Excavation in Boston

TLDR

The study applies a finite‑element model to simulate the top‑down construction of a seven‑story underground parking garage at Boston’s Post Office Square. The model couples soil flow and deformation, uses a numerically accurate excavation algorithm for nonlinear soil, and incorporates advanced clay constitutive behavior, with predictions validated against field data on wall deflections, soil deformations, surface settlements, and piezometric elevations. Comparisons reveal that wall‑movement discrepancies stem mainly from post‑construction shrinkage, settlement errors arise from unrealistic piezometric elevation modeling, and a modified analysis that accounts for these factors yields close agreement, demonstrating that advanced analysis can reliably predict soil deformations and groundwater flow if the full soil profile is adequately characterized.

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.