Tunneling Complete! Project Readies for Pipe Installation.
The contractor for the Bay Tunnel completed excavation to the Newark Shaft in early January—6 months early. The project is now preparing to extract pieces of the cutter head from the tunnel boring machine (TBM) at the retrieval shaft and prepare for the next phase.
The next step for the Bay Tunnel Project is the installation of a 5-mile pipeline that will link the existing segments of BDPL Nos. 1 and 2 and the future BDPL No. 5 in the East Bay with those on the Peninsula. The pipe installation will begin from the Peninsula shaft lowering the pipe spools, placing them on a carrier connected to a railroad car and delivering them through the tunnel to the Newark Shaft where the first segment will be installed. The end of each pipe spool will be fit and welded to connect and secure each joint. The Contractor expects to complete installing the pipe liner in early fall 2013.
Different from the more traditional method used to excavate the launch shaft in the Peninsula; the Bay Tunnel Project utilized freezing ground technology to build the receiving shaft. Crews froze the ground before excavating the shaft by installing 50 freezing pipes, each 128-feet-long that formed a 28-foot-diameter circle to shape the tunnel shaft, so that the contractor could excavate solid material.
The overall Bay Tunnel project is more than 80 percent complete.
|40-feet diameter pipe segments will be installed inside the tunnel.
||Newark shaft in early morning after the tunnel boring machine holed through.
The new Bay Tunnel will link the existing segments of BDPL Nos. 1 and 2and the future BDPL No. 5 in the East Bay with those on the Peninsula. The existing portions of BDPL Nos. 1 and 2, which were built in the 1920’s and 30’s, lay along the bay floor and on trestles that cross over environmentally sensitive marsh land. The pipe and the trestle are in a deteriorated condition. The Bay Tunnel will bypass these environmentally sensitive wetlands.
The tunnel will extend 5 miles under San Francisco Bay at depths of up to 100 feet and it will be constructed using a specialized Earth Pressure Balance Tunnel Boring Machine. The excavated diameter will be 15-foot with a final tunnel lining of 9-foot diameter welded steel pipeline. At each end there will be a vertical shaft, and it will connect the BDPL Nos. 1, 2, and 5 piping manifold. The spoils resulting from excavation during this project are anticipated to be used as part of the South Bay Salt Pond Restoration Project, conversion of adjacent salt ponds to marshland. The portion of the existing BDPL Nos. 1 and 2 that are replaced by the tunnel will be capped on each end and will be abandoned in place.