This month will see the lowering of the Robbins TBM to the base of Shaft 5A for tunnelling to begin on the final section of the MetroWest Water Supply Tunnel in Boston, US. The contract, CP-3A, covers the construction of a 1.2km long, dog leg tunnel between Shaft 5A and Shaft W.
Shea/Traylor/Healy JV (STH) was awarded the $57.3m CP-3A contract by the Massachusetts Water Resources Authority (MWRA) in October 1998. A 100m starter tunnel and tail tunnel have been mined out using a tracked Alpine roadheader in preparation for TBM boring to begin. The JV has transferred the 5.4m diameter Robbins TBM after it finished the 8.5km long westbound CP-2 drive in July 1999 from shaft E to the base of the 75m deep Shaft 5A. This was excavated by contractor LMAC/LLC at a cost of $5.7m.
The tunnel will be driven through altered argillite, argillite, volcanic rocks and granite and will be lined with cast in-situ concrete, reinforced if necessary, and steel lined through a fault zone.
Now that the tunnelling work on CP-2 Westbound is complete, formwork is being transported to the westbound heading at Shaft L for concrete lining to begin. After recovering from the main bearing problems on the Robbins TBM in February 1999, (June ’99, p7), STH has reached the half way mark at 5.9km of the 10.5km long drive on the the CP-2 east bound tunnel.
The 7.9km long third drive, CP-1, is scheduled for completion in February 2000. This section is being constructed by contractor, MetroWest Tunnellers, an Obayashi-Modern Continental JV, at a cost of $144.5m. The JV is using a CTS designed 5.4m diameter lattice beam TBM with full shield.
Tunnel excavation is scheduled for completion in 2001 with the $728m MetroWest system coming on-line in 2003.
Related Files
Boston Metro West Supply System
