USA

Suffolk County Outfall Replacement Project

Owner/Client:

Suffolk County, NY/OHL – Posillico - SELI Overseas Joint Venture

Cost of works:

USD 188 million

Period of Activity:

2018 - 2019

The Bergen Point Wastewater Treatment Plant (WWTP), owned and operated by Suffolk County Department of Public Works, discharges treated effluent into the Atlantic Ocean through an outfall that passes beneath the Great South Bay and underneath Jones Beach. The 14,200-foot-long segment of the outfall that extends from the WWTP to the Jones Beach Island and passes underneath Great South Bay, has been determined to be in a failing condition and replacement is necessary.


— Project Description:

The Project involves the construction of a new 10-foot ID tunnel through a mixture of soft soil materials under the Great South Bay. The new 2.6-mile tunnel will address the concerns of potential failure of the current pipe and will have a longer lifespan. No carrier pipes will be installed inside the tunnel; the lined tunnel itself will serve as the replacement outfall.
The TBM entry and exit shafts are constructed using ground freezing techniques and extend to a depth of 80 to 100 feet below ground level. The tunnel is being excavated using a mixshield TBM and lined with 48-inch-wide precast concrete segment rings. The shaft construction is divided into major work phases including site preparation, excavation of the launch shaft and installation of the new mixshield TBM.
The scope of work also calls for replacement of the pipe and valves at the existing Final Effluent Pump Station, installation of the new site piping, gates, valve chamber, meter chamber, chamber 3B, and set up of staging and mucking areas. Piping work on the Barrier Island will extend from the receiving shaft to the new connection at the existing outfall.

— Description of Services:

• Outfall tunnel segmental lining detailed design;
• TBM face pressure analysis and verification of TBM thrust;
• Detailed design of flood protection for shaft excavation;
• Liner structural design for pipe jacking stretch;
• Structural design of transition pipe (pipe jacking – segmental lining);
• Feasibility study of VSM option in lieu of ground freezing solution for shaft excavation;
• Preliminary design of TBM receiving shaft support with adoption of secant piles and bottom plug;
• TBM excavation face stand-up time analysis.

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