Finite Element Analyses of an Urban Cofferdam Using Hypoplasticity Clay Model

Urban cofferdams are used to build the rigid central core of high-rise buildings and are conceived as temporary retaining excavation structures. For the case of the One Museum Park West (OMPW) building (Chicago, IL), settlement points and inclinometer data were recorded during the excavation within the cofferdam. This cofferdam stage represented 20% of the total excavated volume of this project and caused about a third of the total measured settlements. An axisymmetric numerical model using an advanced constitutive soil model, the hypoplasticity model for clays with intergranular strains, is developed to simulate an idealized lower bound solution of the ground movements resulting from the OMPW cofferdam excavation. Significant differences between computed and observed ground movements are presented when compliance effects between structural members, installation of nearby foundations, and flexibility of the cofferdam and internal bracing connections are ignored.