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WMATA to test use of 'curtain grouting' on Red Line tunnel


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#1 KevinKorell

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Posted 28 June 2017 - 01:48 PM

Beginning July 10, D.C. Metro and its contractor will test the use of a “curtain grouting” technique to add a waterproof membrane to the exterior of Red Line tunnel walls using a proprietary polymer-based material.

“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 GM/CEO Paul J. Wiedefeld.

Last Friday, for example, Red Line service had to be suspended in two separate areas due to arcing insulators caused by water infiltration during the morning commute. The dual incidents led to widespread delays, crowding and inconvenience for tens of thousands of riders.

What is curtain grouting?
Curtain grouting is a leak-mitigation technique used to treat an entire area that is leaking by adding a rubberlike membrane on the outside of the concrete tunnel wall. To do this, holes are drilled in the ceiling of the existing tunnel until the exterior of the tunnel is reached. From there, a proprietary polymer-based emulsion (PBE) grout is injected into the hole at high pressure, which begins cascading down the curved exterior of the tunnel (like the way chocolate syrup cascades down an ice cream sundae). Two holes are drilled every 10 feet for the injections. The holes are then sealed at the conclusion of the process. The injected material forms a rubberlike impenetrable membrane, or “curtain,” between the exterior of the tunnel wall and the surrounding ground medium.

The contractor has successfully used this solution in the mining industry to seal ground water inflows — some with flow rates of 50 gallons per second.

Metro plans to test this technique in the two different environments that exist along the Red Line segment — one in a linear bored tunnel and one in a blasted-rock cavern. The linear tunnel segment that will be used for the pilot will be a 2,000-foot section of the inbound track between Medical Center and Bethesda. For the second test location, Metro plans to use the entire Medical Center interlocking area, which is a cavernous space that was constructed out of blasted rock.

Tunnel designed to leak
The nine-mile long deep-tunnel segment between Farragut North and Grosvenor is the oldest bored section of the Metrorail system and was designed and constructed prior to the widespread use of NATM, the New Austrian Tunneling Method, which provides tunnels with a waterproof membrane. Engineers designed the Red Line tunnel to leak, knowing that it would be well below the groundwater table and under high hydrostatic pressure. The tunnels have leaked, by design, since they were constructed and massive drainage pumping stations remove millions of gallons of water every week.

The lack of a waterproof membrane has posed significant maintenance challenges for Metro. First, the presence of moisture and dripping water is a leading cause of arcing insulators. More than two thirds of all arcing insulators occur along this section of the Red Line. Second, water corrodes the track bed, rails, fasteners communication cables, pipes and other components, all of which must be replaced more frequently in this area. Finally, the water entering the tunnels carries mineral deposits that accumulates as a “muck like” substance in switches and other components that are needed for train movement. (By contrast, all other deep Metro tunnels were designed using NATM and are quite dry by comparison to the western Red Line.)

For years, Metro has relied on a strategy of “negative side grouting,” where individual leaks are addressed from the inside of the tunnel. This approach has limited effect, because the hydrostatic pressure outside the tunnel is strong enough that the water will simply find another path. For several years prior to 2011, Metro stopped trying to keep the interlocking (crossover location) at Medical Center in service because it required daily visits by maintenance crews to remove the muck.

Evaluating the Pilot
Metro has moved quickly to have the work associated with the pilot occur during the summer months when ridership is lighter. Evaluation of the pilot will occur during the autumn rainy season, when hydrostatic pressure builds and water infiltration is more prevalent. By early 2018, Metro engineers should be in a position to judge the effectiveness of the curtain grouting process in the Metro environment.

Wiedfeld cautioned that the pilot area represented less than 3 percent of the affected area of the Red Line, and that any eventual full-scale solution would take time and a significant amount of capital funding to advance.


Keywords

D.C. Metro   electrical arcing event   Paul J. Wiedefeld   rail infrastructure   rail safety   rail tunnel   subway   Washington Metropolitan Area Transit Authority   water infiltration   water leaks   WMATA   

 

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#2 CNJRoss

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Posted 28 June 2017 - 09:04 PM

WMATA news release 6/28/17:

 

Metro to test new waterproofing of Red Line tunnels

 

 

Metro has approved a pilot program that could have long-term benefits for Red Line riders. 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 using a proprietary polymer-based material.

 

"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.

 

Last Friday, for example, Red Line service had to be suspended in two separate areas due to arcing insulators caused by water infiltration during the morning commute. The dual incidents led to widespread delays, crowding and inconvenience for tens of thousands of riders.

 

"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.

 

About the Pilot

Curtain grouting is a leak-mitigation technique used to treat an entire area that is leaking by adding a rubberlike membrane on the outside of the concrete tunnel wall. To do this, holes are drilled in the ceiling of the existing tunnel until the exterior of the tunnel is reached. From there, a proprietary polymer-based emulsion (PBE) grout is injected into the hole at high pressure, which begins cascading down the curved exterior of the tunnel (like the way chocolate syrup cascades down an ice cream sundae). Two holes are drilled every 10 feet for the injections. The holes are then sealed at the conclusion of the process. The injected material forms a rubberlike impenetrable membrane, or "curtain," between the exterior of the tunnel wall and the surrounding ground medium.

 

The contractor has successfully used this solution in the mining industry to seal ground water inflows - some with flow rates of 50 gallons per second.

 

Metro plans to test this technique in the two different environments that exist along the Red Line segment - one in a linear bored tunnel and one in a blasted-rock cavern. The linear tunnel segment that will be used for the pilot will be a 2,000-foot section of the inbound track between Medical Center and Bethesda. For the second test location, Metro plans to use the entire Medical Center interlocking area, which is 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, Montgomery County Council 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." 

 

Service Information

Drilling more than 500 holes in the tunnel ceiling and injecting high-pressure grout is a time-consuming process that can only occur when trains are not running. To advance the pilot, Metro is today announcing the following service changes:

 

Weeknights

Beginning Monday, July 10, and continuing every weeknight (Monday-Friday) through Friday, August 11, Red Line trains will single track between Friendship Heights and Medical Center starting at 9 p.m. nightly. During the overnight hours, Metro and its contractor will advance the curtain grouting process in the linear tunnel segment.

 

Weekends

In order to inject the curtain grouting into the Medical Center interlocking cavern, train service will need to be suspended on both tracks for four consecutive weekends. Free shuttle buses will replace Red Line trains between Grosvenor and Friendship Heights on the following dates:

  • Saturday, July 15 and Sunday, July 16
  • Saturday, July 22 and Sunday, July 23
  • Saturday, July 29 and Sunday, July 30
  • Saturday, August 5 and Sunday, August 6
Background

The nine-mile long deep-tunnel segment between Farragut North and Grosvenor is the oldest bored section of the Metrorail system and was designed and constructed prior to the widespread use of NATM, the New Austrian Tunneling Method, which provides tunnels with a waterproof membrane. Engineers designed the Red Line tunnel to leak, knowing that it would be well below the groundwater table and under high hydrostatic pressure. Since construction, the tunnels have leaked, by design, and massive drainage pumping stations have removed millions of gallons of water per week.

 

The lack of a waterproof membrane has posed significant maintenance challenges for Metro. First, the presence of moisture and dripping water is a leading cause of arcing insulators. More than two thirds of all arcing insulators occur along this section of the Red Line. Second, water corrodes the track bed, rails, fasteners, communication cables, pipes and other components, all of which must be replaced more frequently in this area. Finally, the water entering the tunnels carries mineral deposits that accumulates as a "muck like" substance in switches and other components that are needed for train movement. (By contrast, all other deep Metro tunnels were designed using NATM and are quite dry by comparison to the western Red Line.)

 

For years, Metro has relied on a strategy of "negative side grouting," where individual leaks are addressed from the inside of the tunnel. This approach has limited effect, because the hydrostatic pressure outside the tunnel is strong enough that the water will simply find another path. For several years prior to 2011, Metro stopped trying to keep the interlocking (crossover location) at Medical Center in service because it required daily visits by maintenance crews to remove the muck.

 

Evaluating the Pilot

Metro has moved quickly to have the work associated with the pilot occur during the summer months when ridership is lighter. Evaluation of the pilot will occur during the autumn rainy season, when hydrostatic pressure builds and water infiltration is more prevalent. By early 2018, Metro engineers should be in a position to judge the effectiveness of the curtain grouting process in the Metro environment.

 

Wiedefeld cautioned that the pilot area represented less than 3 percent of the affected area of the Red Line, and that any eventual full-scale solution would take time and a significant amount of capital funding to advance.

 

"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."

 

Additional Information
 

 

 
 


#3 CNJRoss

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Posted 28 June 2017 - 09:11 PM

WTOP radio, 6/28/17:

 
Part of Metro’s Red Line to shut down for multiple weekends for water seal work

 

WASHINGTON — The Red Line will shut down four consecutive weekends in July and August between Grosvenor-Strathmore and Friendship Heights to allow for testing of a sealant that could help prevent some major Red Line delays like last Friday’s shutdowns.

 

During the shutdowns, Metro will test a new tunnel sealant meant to limit the amount of water that seeps into the nine miles of Red Line tunnels in that stretch. The water issues have been a problem for decades. Among other issues, the leaks and added grime increase the risk of smoke incidents like arcing insulators.

 

The area getting the sealant is only 3 percent of the most troubled parts of the Red Line, so long-term fixes for other areas remain a long way off.

 

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#4 CNJRoss

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Posted 19 September 2017 - 07:19 AM

WTOP radio 9/18/17:
 

More Red Line shutdowns possible as Metro expands efforts to plug tunnel leaks

 

 

WASHINGTON — Metro is considering more shutdowns of the Red Line through the Bethesda area to expand new efforts to seal up persistent leaks in the tunnel that can contribute to smoke incidents and deteriorating tracks.

 

Metro is analyzing how the first round of drilled and filled holes in the tunnel walls is holding, General Manager Paul Wiedefeld said, before deciding whether to exercise a contractual option for a second stretch of work.

 

“Definitely, it’s made a difference, but we’ve got to make a judgment of whether or not we think this is worth further investment or even further testing,” Wiedefeld said. “The early indications are very good.”

 

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#5 CNJRoss

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Posted 28 September 2017 - 04:34 PM

WMATA news release 9/28/17:

 
Metro Red Line waterproofing pilot to be expanded amid signs of improvement

 

 

Metro today announced that a water leak mitigation project on the Red Line will be expanded. Early results from the pilot, which began in July, shows the installation of a new waterproofing membrane outside the Red Line tunnel is reducing water infiltration in two test segments.

Work by Metro and its contractor will continue on an additional 4,000 foot-section of inbound track between Medical Center and Grosvenor that will triple the area of deep tunnel segment under the pilot from the initial scope.

The leak mitigation pilot is testing the use of a "curtain grouting" technique in which a proprietary polymer-based material is injected through holes drilled into the tunnel ceiling to form a waterproof membrane on the exterior of the tunnel walls.

In the two test segments – a 2,000-foot section of inbound track between Medical Center and Bethesda and the entire Medical Center interlocking – the tunnels have remained relatively dry, even with excessive rains in late July and August that brought up to more than three inches of precipitation in one day.

The deep tunnel segment of the Red Line between Dupont Circle and Grosvenor was constructed prior to widespread use of NATM, the New Austrian Tunneling Method, which provides tunnels with a waterproof membrane. The area is well below the water table and subject to high hydrostatic pressure that makes it prone to water infiltration that more quickly corrodes track infrastructure.

Injecting the curtain grouting requires drilling hundreds of holes through the tunnel ceiling and can only be done when trains are not running. The expanded scope of the project will require approximately six weeks, including two weekend shutdowns where buses will replace trains through the area. 

 

In order to safely and effectively continue the pilot, Metro is announcing the following service changes:

SERVICE INFORMATION

WEEKDAYS

On weeknights from October 16 through November 24, Red Line trains will single track between Medical Center and Grosvenor starting at 9 p.m. Minor delays are expected.

WEEKENDS

Free shuttle buses will replace Red Line trains between Medical Center and Grosvenor stations on the following two weekends:

  • Saturday and Sunday, October 28, 29
  • Saturday and Sunday, November 18, 19

In addition, Red Line trains will single track between Medical Center and Grosvenor on the following two weekends:

  • Saturday and Sunday, October 21, 22
  • Saturday and Sunday, November 11, 12

Finally, Red Line trains will single track between Medical Center and Twinbrook to accommodate other track work on the following weekend:

  • Saturday and Sunday, November 4, 5

More information

 



#6 CNJRoss

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Posted 15 December 2017 - 08:05 PM

WTOP radio 12/15/17:

Red Line tunnel work to disrupt night, weekend service through February

 

 

WASHINGTON — Red Line trains will share a single track most nights and weekends through mid February as part of the next round of work aimed at reducing the flow of water into the tunnels, Metro said Friday.

 

The single-tracking will occur in stretches between the Friendship Heights and Grosvenor-Strahthmore stations beginning Dec. 22. But the disruption will likely reduce service along the entire length of the Red Line.

 

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#7 CNJRoss

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Posted 15 December 2017 - 11:27 PM

WMATA news release:

 
Metro advises customers of Red Line service changes due to expanded waterproofing pilot

 

Red-Line-Leak-Mitigation.jpg

Metro is advising customers of evening and weekend service changes on the Red Line starting Friday, December 22, and continuing through Thursday, February 15, in order to extend a water leak-mitigation project and improve reliability.

The pilot, which began in July, is using a new waterproofing technique to reduce water infiltration in the Red Line's deep tunnel segments that are prone to leaks. The pilot was expanded in October following early results that showed improvement in keeping the tunnels dry.

During the project, trains will single track during the evening and late night hours on weeknights, in addition to weekends, to allow Metro and its contractors to install a new waterproof membrane using a "curtain grouting" technique that requires drilling hundreds of holes through the tunnel ceiling and injecting a proprietary polymer-based material through the holes to form a protective layer on the exterior of the tunnel walls.

The leak mitigation pilot began with two test segments - a 2,000 foot section of inbound track between Medical Center and Bethesda and the entire Medical Center interlocking. A third test segment tripled the size of the initial pilot - with an additional 4,000 foot-section of inbound track between Medical Center and Grosvenor.

The deep tunnel segments on the Red Line between Dupont Circle and Grosvenor are well below the water table and were built before the widespread use of NATM, the New Austrian Tunneling method, which provides a tunnel with a waterproof membrane. As such, the tunnels are subject to water infiltration from the high hydrostatic pressure that can cause track infrastructure to more quickly corrode.

Due to the extensive length of the tunnel segment the project is expected to take eight weeks (including 9 weekends) to complete the work. During this time Metro will implement the following service changes:

SERVICE INFORMATION

Red Line trains will single track as follows:

Medical Center - Grosvenor
Weeknights (Mon-Thurs)
December 26-28, January 2-4, 8-11 9 p.m. through closing nightly

Weekends
December 22-24 6 p.m. Friday through closing Sunday
December 29-31 9 p.m. Friday through 6 p.m. Sunday

Friendship Heights - Grosvenor
Weeknights (Mon - Thurs)
January 16-18, 22-25 9 p.m. through closing nightly

Weekends
January 13-15 7 a.m. Saturday through closing Monday
January 20-21 7 a.m. Saturday through closing Sunday

Friendship Heights - Medical Center
Weeknights (Mon-Thurs)
January 29-February 1, 5-8 and 12-15 9 p.m. through closing nightly

Weekends:
January 27-28, February 3-4 and 10-11 7 a.m. Saturday through closing Sunday

At this time the work involves single tracking only. Metro will update customers if there are any changes to the service plan. For the most up-to-date information, visit Metro's upcoming track work page on wmata.com or sign up for MetroAlerts to receive text or email messages.

 





 

 





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