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Pawtucket CSO Tunnel Project

Narragansett Bay Commission (NBC)

Narragansett Bay Commission (NBC) has commissioned the third and final phase (Phase IIIA) of Pawtucket CSO tunnel project. This phase of the program will be executed as a Design-Build project and is focused primarily on the Bucklin Point Service Area. Phase IIIA includes a 30 ft (9.1 m) ID TBM tunnel, ancillary underground features (i.e. drop shafts, launch shaft, receiving shaft, tunnel pump station shaft, adit tunnels) to support the functionality of the tunnel to serve as a Combined Sewer Overflow (CSO) storage facility. The tunnel is designed to have sufficient volume to store all contributing overflows during a storm event up to the three-month storm for subsequent pump-out and treatment at the BPWWTF.

Design Services for Large Diameter Shaft, SEM Tunnels and Adits, IDV for Segmental Lining:

Gall Zeidler Consultants is responsible for the temporary and permanent works design of all SEM tunnels, the permanent works design for large diameter shafts, and the design of the temporary and permanent adit connections to the TBM segmental lining. The design of the adit connections to the TBM liner include the design of specialized TBM segments and shear-coupling elements around the break-out area, as required. In addition, Gall Zeidler Consultants is providing Independent Design Verification (IDV) services for the TBM Segmental Lining, which covers a full check of temporary and permanent loading of the liner along the entire alignment.


Providence, Rhode Island


2020 - Present


TBM Storage Tunnel, Large Diameter Shafts, SEM Tunnels, SEM Adits, TBM-Adit Connections


Approx. 2.2 miles (3.5 km) – TBM
Approx. 850 feet (260 m) – SEM Tunnels


30.0 ft (9.1 m) – TBM Internal Diameter
~39.0 ft (11.9 m) – SEM Starter Tunnel
~11.0 ft (3.4 m) to ~18.0 ft (5.5m) – SEM Adits


Man-made granular fill, Glaciofluvial sands, Rhode Island formation (sandstone with lesser amounts of conglomeratic sandstone and siltstone, and small amounts of mudstone, shale, and coal)


US $368 Million




Narragansett Bay Commission (NBC)