A pre-bid meeting is scheduled for May 10 this year for the tunnel construction contract on Phase 1 of the three phase Narragansett Bay Commission Combined Overflow Facilities (CSO) Program, Rhode Island, US. Contract 01:302.06-C is the single largest package on the scheme for Providence City and includes a 5.3km long tunnel, adits, work shafts and a pump station cavern.
The main element of the work is an 8.5m id main spine tunnel that will be excavated at a depth of 82m by TBM and lined with pre-cast concrete segments. Another major feature is the main shaft, S1 that will be an 8.5m diameter, 92m deep concrete lined slurry or freeze wall construction excavated by drill and blast. Also included is the construction of a 2.9m diameter, 78.9m deep drop shaft and a 1.1m diameter, 78.9m deep vent shaft both excavated by blasting, drilling or raise boring. Drill and blast will be used to excavate some 1.3km of 1.5m -5.2m diameter concrete lined adits and deaeration chambers. Excavation of the 21m high x 20m wide x 38.5m long tunnel pump station cavern is included in the contract, also utilising drill and blast. This section includes a 10.5m diameter, 100m deep concrete lined access shaft, a 3.6m diameter, 100m deep concrete lined hoisting shaft and a 1.6m diameter, 75.6m long suction tunnel. Currently an 8.5m diameter, 80.4m deep concrete lined foundry shaft is included but may be let as a separate package.
Client, The Narragansett Bay Commission (NBC) envisage up to 10 separate construction contracts made by public bid on phase 1 with a 70 month completion schedule. Already on board is The Louis Berger Group as Program Manager, a JV of Gilbane/Jacobs Associates as Construction Manager and Jacobs/Svedrup as Project Design Engineers.
Bid opening is expected in July this year with contract award currently slated for early October. If the schedule runs to plan, notice to proceed is planned for mid to late October.
The CSO Program is planned to reduce discharge of combined sewage into the NBC service area using the tunnel for collection and transfer of sewage for pumping and treatment after a rain event. The complete scheme is planned to be completed in 22 years.
