Bi-County Water Tunnel

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June 2010 Update

The Bi-County Water Tunnel Project has moved into its next phase – boring a 5.3 mile tunnel that will house 84-inch pipe. The new line will connect an existing water main near I-270 and Tuckerman Lane to an existing water main in Rock Creek Park at Stoneybrook and Beach Drives. The connection will allow WSSC to meet future capacity requirements for Montgomery and Prince George’s counties. The new line will be able to carry 100-million gallons of water a day.

Planning for the $168-million dollar project began in 2004, community outreach in early 2005. Work during the last half of 2009 and first half of 2010 concentrated on constructing three shafts to provide access for and retrieval of a Tunnel Boring Machine (TBM). The main access shaft near Connecticut Avenue just outside the Washington Beltway is finished. The shaft at Stoneybrook is nearing completion, and work on the Tuckerman shaft begins later this year. (See our archive for detailed background information and maps showing the project. We also have a photo gallery showing progress at the sites and highlights of the operation. We will add to the gallery as work progresses.)

The Connecticut Avenue shaft is 164-feet deep and 35-feet in diameter.  Workers created two horizontal 150-foot tunnels off the shaft to make room for assembly of the 184-foot Tunnel Boring Machine. Dynamite was used during much of the process. The last blast at the Connecticut Avenue shaft was on the morning of June 11th, 2010.

Local officials, WSSC Commissioners and the media had a chance to see the TBM firsthand before its pieces were lowered to the floor of the shaft for assembly and tunneling. They received detailed explanations of how the machine will work below the surface. They also saw the railroad system that will follow behind the TBM to remove debris, and a chance to peer down into the huge shaft.

The Tunnel Boring Machine

The TBM for this project is named, “Miss Colleen,” after the wife of the project superintendent when the machine started its first job in 1993. The name has stayed the same, but Miss Colleen has undergone 10 enhancements, each one to meet the specifications of the next project. The current configuration boosts her horsepower from 800 to 1200.

The TBM has a 10-foot cutting head made up of twenty-one 17-inch carbide cutting heads that chew through rock at a projected advance rate of 100 feet per day. The cutting head is powered by electricity – a new substation built on the Connecticut Avenue site to provide the power. A series of special “baloney cable” extension cords will be added as the TBM moves through the rock.

The Pipe

Northwest Pipe Company is providing the pipe from its Parkersburg, WVA plant. The 7-foot diameter pipe comes in 50-foot sections, and is lined with ½-inch cement mortar. After the sections are welded together and tested, workers will add about 18-inches of cement grout to fill the space between the pipe and the rock. Workers will “hand pack” cement mortar at each welded joint on the interior of the pipe.

How the Process Works

The TBM will begin its journey on the floor of the Connecticut Avenue shaft pointing toward its Stoneybrook destination to the East. A train of “muck” cars will follow the machine as it cuts the tunnel and disposes of the rock. A small 40-horsepower locomotive will pull the train of full cars back to the Connecticut Avenue shaft where they will be hoisted to the surface, dumped and returned to service. Each car can carry 9 tons of rock. As the first train of cars heads back to the shaft to be emptied, a second train waiting on a sidetrack moves into place.

When the Stoneybrook portion of the tunnel is complete the Tunnel Boring Machine will back up to the Connecticut Avenue shaft, be dismantled, reassembled facing the opposite direction and made ready for the longest part of its journey. When the TBM reaches its Tuckerman destination, the machine will be dismantled and hoisted from the shaft to be shipped to its next project.

A lot of work remains before the Bi-County Water Tunnel Project is complete, so please check back for updates.