Abstract:
As the demand for housing in West Coast cities like San Francisco continues to grow, the need to redevelop parcels adjacent to existing buildings and transportation structures continues to drive the need for innovative systems of shoring, ground improvement, underpinning, and dewatering. As a part of Mid-Market development in San Francisco, the 950-974 Market St. redevelopment project is located adjacent to BART and Muni tunnels. The site soil profile consists of urban fill and dune sand over bay mud and Colma formation with a watertight depth of 25-ft. The redevelopment project consisted of a 12-story build over 2 levels of water tight parking. BART requires that the water table adjacent to its structures not to be lowered more than 2-ft. This requirement resulted in an elaborate watertight shoring system with a system of deep wells, monitoring wells, and reinjection wells between the excavation and the BART tunnel. In addition to use of water tight DSM shoring to protect the BART structure, water tight underpinning of an adjacent building led to the use of slant piles and jet grouting. Following successful completion of the shoring and temporary dewatering, a grid pattern of DSM was installed to carry the static load for the building mat foundation and to provide mitigation of seismic liquefaction risks.