RUI: Effects of Pre-Excavation Activities on the Performance of Urban Cofferdams

California State University-Long Beach Foundation, Long Beach CA

Investigators

Abstract

The recent tendency in urban excavations for high-rise buildings is the use of cofferdams which at times are responsible for the majority of the resulting ground movements. As a result of these projects, the allowable ground movements imposed by underground regulatory agencies have been drastically reduced, calling for improvements in the observational and analytical methods used in movement control plans. This award supports fundamental research on the methods of analysis and design of urban cofferdams and presents an opportunity for advances in soil-structure interaction behavior of deep excavations. Design recommendations considering the proposed effects in the performance of cofferdams do not currently exist in the United States. Two urban cofferdams serve as the test bed of this research: the first was built for a structure projected to be the tallest building in the United States, and to have the deepest basement ever built in the city where the structure was proposed; the second was built for the One Museum Park West building in Chicago, Illinois. The fundamental knowledge developed in this research will inspire new methods of analysis and design of offshore structures, deep foundations, wharfs, and retaining structures, and will advance the understanding of the soil-structure interaction in other types of geotechnical projects. Knowledge will be produced on the behavior of sheet pile interlocks in urban cofferdams under compression loading, the concrete material time-dependent effects on the behavior of cofferdams braced with reinforced concrete ring beams, and slippage and rotation at sheet pile interlocks for urban cofferdams braced with segmental steel ring beams. Three-dimensional fully-coupled flow-deformation numerical analyses of urban cofferdams using advanced constitutive soils models and incorporating the small strain behavior of soils will be used in the analyses. New design methodologies oriented for practice will be developed to incorporate the following factors into the design process: the material time-dependency of reinforced concrete ring beams, the structural compliance of steel ring beams and sheet piles, the slippage and rotation at sheet pile interlocks, and the installation of deep foundations and other structures inside of cofferdams. The ultimate goal of this research is to create more sustainable and resilient urban environments by preserving and protecting existing infrastructure, which is often compromised when excessive deformations occur.