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WMATA Tests New Waterproofing Method

The Washington Metropolitan Area Transit Authority, the transit agency for the Washington, D.C., area that's known as Metro, announced it will test new waterproofing of its Red Line's tunnels in a pilot program. Beginning July 10, Metro and its contractor will test the use of a curtain grouting technique to add a waterproof membrane to the exterior of the tunnel walls.

"Since this tunnel segment was constructed, Metro has fought a battle against Mother Nature, and Mother Nature has always had the upper hand," said Metro General Manager and CEO Paul J. Wiedefeld, noting Red Line service recently was suspended in two locations because of arcing insulators caused by water infiltration during the morning commute. The incidents caused widespread delays, crowding, and inconvenience for thousands of passengers.

"Just as we have addressed the root causes of track infrastructure problems and railcar reliability issues, I want to address the water infiltration problem head on and find a sustainable solution. Our Red Line riders deserve nothing less," Wiedefeld said.

Curtain grouting treats an entire area that is leaking by adding a rubber-like membrane on the outside of a concrete tunnel wall. To do this, holes are drilled in the ceiling of the existing tunnel until the exterior of the tunnel is reached, and a proprietary polymer-based emulsion grout is injected into the hole at high pressure. Two holes are drilled every 10 feet for the injections, and the holes are sealed at the conclusion of the process. The result is a membrane, or "curtain," between the exterior of the tunnel wall and the surrounding ground medium.

Metro reported the contractor has successfully used this solution in the mining industry to seal groundwater inflows and that it plans to test this technique in two locations along the Red Line, one being a 2,000-foot section of inbound track and the other a cavernous space that was constructed out of blasted rock.

"Red Line riders will greatly benefit if this innovative approach to preventing water from entering the system works," said Roger Berliner, the Montgomery County Council's president. "As everyone knows, water and electricity are not a good combination. While there will be unavoidable disruptions, in the long run, our community will be much better served if this approach works out."

To allow the work to take place Red Line service from July 10 on weeknights through Friday, Aug. 11, will take place on a single track between Friendship Heights and Medical Center starting at 9 p.m. nightly. During four consecutive weekends starting July 15-16, train service will be suspended and free shuttle buses will move passengers between Grosvenor and Friendship Heights.

By early 2018, Metrl should be able to judge the success of the project. "This kind of capital project perfectly illustrates why we need a dedicated funding source for our Metro system," said Metro Board Chair Jack Evans. "Fixing this problem will not be cheap or easy, but it is absolutely necessary and the right thing to do."

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