Metro Announces Pilot Program To Try To Fix Leaky Red Line Tunnel
Installation of waterproofing will cause single-tracking and close a large track segment on weekends in the Bethesda area over the summer
Bethesda Metro station
Bethesda Beat file photo
Metro will test a waterproofing technique developed by the mining industry to try to stop water from leaking into a Red Line tunnel segment in Bethesda.
The transit operator announced Wednesday it will single-track trains on weekday evenings from July 10 through August 11 and close both tracks running through the Medical Center and Bethesda stations on certain weekends in July and August so crews can install the waterproofing.
The announcement comes a day after Metro General Manager Paul Wiedefeld told the Montgomery County Council that the transit agency was close to cutting a deal to test new waterproofing technology in the tunnel where arcing insulator incidents caused long delays during Friday morning’s commute. The approximately 9-mile tunnel between the Grosvenor-Strathmore and Farragut North stations is the only one built without a waterproof membrane—and is particularly prone to groundwater seepage in the Bethesda area.
The waterproofing technique is called curtain grouting and involves injecting a polymer-based emulsion grout into holes drilled in the tunnel’s walls. The grout would then drip down the curved walls “like the way chocolate syrup cascades down an ice cream sundae,” according to Metro.
The grout would form a “rubberlike impenetrable membrane, or ‘curtain,’ between the exterior of the tunnel wall” and the ground, Metro said in a news release. Metro said its contractor “has successfully used this solution in the mining industry to seal groundwater inflows.” The transit operator did not name its contractor and did not include the cost of the pilot program in the news release.
Metro will test the material in two Bethesda locations—a 2,000-foot section of the inbound track between the Medical Center and Bethesda stations as well as the Medical Center interlocking area, which Metro described as a “cavernous space that was constructed out of blasted rock.”
Beginning July 10 and continuing every weeknight through August 11, Red Line trains will single-track starting at 9 p.m. between the Friendship Heights and Medical Center stations so crews can install the curtain grouting in the track tunnel.
Metro will close both tracks passing through the Medical Center and Bethesda stations on the weekends of July 15-16, 22-23 and 29-30 and Aug. 5-6 to install the material in the interlocking cavern. On these weekends the transit operator will offer free shuttle bus service between the Strathmore-Grosvenor and Friendship Heights stations.
Metro said water leaking into the tunnel has caused the arcing insulator incidents—which involve smoke created by muck from the tunnel floor splashing onto the electrified third rail—and also corroded track bed, rails, communication cables and other components in the tunnel.
“Since this tunnel segment was constructed, Metro has fought a battle against Mother Nature, and Mother Nature has always had the upper hand,” Wiedefeld said in Wednesday’s statement. “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.”
The transit operator plans to evaluate the pilot program during the fall and said it should be able to judge its effectiveness by early 2018.
Wiedefeld said in the news release that the pilot will be tested on only 3 percent of the affected part of the Red Line tunnel and a full-scale solution would take more time and a significant financial investment.