Boston Project Uses a Triple Dip of Tunneling Technology

...the powerplant and an electrical duct bank, both of which lay in the steel-sheeted receiving pit. “We really couldn’t put it anywhere else because that’s where the interceptor connection is,” says Leo G. Martin, senior project manager for Metcalf & Eddy, Wakefield, Mass, the siphon designer. “Because of its length, a steel sleeve was necessary to eliminate soil friction and help preserve the plastic liner.” Laney is working under a $16.3-million subcontract to prime contractor J. Cashman Inc., Quincy, Mass.

Laney workers located in the residential Idlewell section of Weymouth drilled 60 ft under the bed of the Fore River through glacial till, marine deposits, sand and gravel. They started from a cofferdammed salt marsh site supporting a company-built 900,000-lb pulling capacity drill rig, which cost $1.5 million.

NO YARD Powerplant snag delayed start. (Photo by William J. Angelo for ENR)

The line could be charged by July and will be used to test the new pump station. The second bore, which will take about four to six weeks to complete, will be done in July. “We think the combined siphons are the longest and largest diameter horizontal bores in the world,” says Robert A. Scherpf, Metcalf & Eddy vice president. “It’s even more amazing in that it was drilled in residential backyards and on a coastal beach, which required concerted cooperation between the state, local agencies and property owners.”

The $73-million rock tunnel was primarily done by tunnel boring machine and completed by Cambridge, Mass.-based Modern Continental Construction Co. Inc. in July 2003. About 1,900 ft was drill and blast. The interceptor was a $4.8-million microtunneling project completed in September 2002 by Michels Corp., Brownsville, Wis., for J.F. White Construction, Framingham, Mass.

“We needed multiple mining techniques due to size, soils and geography,” says McBride. “Between our $5.5-billion water and wastewater programs, we have done over 35 miles of tunnels. But this project is the first that incorporated three different state-of-the-art techniques.”