Installation of combined sewer overflow (CSO) consolidation conduits in difficult waterfront conditions would have been no easy task as originally designed and bid, using cut-and-cover methods, yet an aggressive Value Engineering (VE) proposal was accepted and the installation accomplished using pipe jacking methods. Five-hundred-and-ten (510) feet of conventional pipe jacking was successfully accomplished to install 54-inch and 30-inch consolidation conduits as part of the Narragansett Bay Commission's (NBC) CSO Control Facilities Program. This paper will present site conditions, a comparison of the original cut-and-cover design and the VE pipe jacking proposal, provide construction details and challenges. The conduits were installed in a narrow strip of land between historic waterfront structures and the Providence River with a portion of the alignment beneath high-tension towers and transmission lines. The ground conditions consisted of urban fill, a soft organic silt deposit, and abandoned power tunnels, slips and wharfs. Bid documents directed an open cut with an Owner-designed secant pile wall support of excavation and installation of reinforced concrete pipe (RCP) for the conduits, and the Contractor's proposed VE largely eliminated open cut and included pipe jacking with sheeted pits. The VE proposal was negotiated and the Contractor successfully completed the pipe jacking using an open-face shield, ground improvement using chemical grouting, Permalok steel casing and high density polyethylene (HDPE) pipe. Several large obstructions, including concrete-filled vaults, abandoned tunnels, timber piles, and steel sheet piling were encountered and excavated from within the pipe jacking shield. Challenges and risks associated with open-cut excavation in a difficult waterfront environment were significantly reduced by implementing the pipe jacking VE change, but were not entirely eliminated.
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