Pipe Jacking in Difficult Urban Waterfront Conditions

摘要

Installation of combined sewer overflow (CSO) consolidation conduits in difficultrnwaterfront conditions would have been no easy task as originally designed and bid,rnusing cut-and-cover methods, yet an aggressive Value Engineering (VE) proposalrnwas accepted and the installation accomplished using pipe jacking methods. Fivehundred-rnand-ten (510) feet of conventional pipe jacking was successfullyrnaccomplished to install 54-inch and 30-inch consolidation conduits as part of thernNarragansett Bay Commission's (NBC) CSO Control Facilities Program.rnThis paper will present site conditions, a comparison of the original cut-and-coverrndesign and the VE pipe jacking proposal, provide construction details and challenges.rnThe conduits were installed in a narrow strip of land between historic waterfrontrnstructures and the Providence River with a portion of the alignment beneath hightensionrntowers and transmission lines. The ground conditions consisted of urban fill,rna soft organic silt deposit, and abandoned power tunnels, slips and wharfs. Bidrndocuments directed an open cut with an Owner-designed secant pile wall support ofrnexcavation and installation of reinforced concrete pipe (RCP) for the conduits, andrnthe Contractor's proposed VE largely eliminated open cut and included pipe jackingrnwith sheeted pits. The VE proposal was negotiated and the Contractor successfullyrncompleted the pipe jacking using an open-face shield, ground improvement usingrnchemical grouting, Permalok steel casing and high density polyethylene (HDPE) pipe.rnSeveral large obstructions, including concrete-filled vaults, abandoned tunnels, timberrnpiles, and steel sheet piling were encountered and excavated from within the pipernjacking shield. Challenges and risks associated with open-cut excavation in arndifficult waterfront environment were significantly reduced by implementing the pipernjacking VE change, but were not entirely eliminated.