Deformations during Cut-and-Cover Construction of MUNI Metro Turnback Project

Abstract

Construction of the MUNI Metro Turnback project involved deep excavations in soft soils along the Embarcadero waterfront in downtown San Francisco, California. The excavations and shoring system were designed by the Engineer of Record to control ground deformations within specified limits in order to minimize the impacts of the deformations on a block of adjacent, settlement-sensitive buildings. The design included estimates of deformations caused by the excavations and other construction activities, evaluation of potential settlements of adjacent buildings, and structural evaluation of the response of the buildings to the estimated settlements. A comprehensive monitoring program combined with an instrumented test section, appropriate contingency measures, and construction controls were planned so as to allow early warning for appropriate response in the event that the deformations exceeded tolerable limits. This paper reviews the subsurface conditions, base stability analyses, and estimated deformations, describes the instrumentation program, and presents a comprehensive summary of the instrumentation measurements. It interprets the instrumentation measurements and draws conclusions regarding the general nature and magnitude of deformations and their impacts on adjacent structures.