Seattle, WA – The $1.9 billion University Link Extension for Seattle’s Light Rail will connect the University of Washington and Capitol Hill to downtown Seattle. The twin-bored tunnels will sit 125 feet underground as they pass underneath homes, business, and even the I-5 freeway. Using a massive tunnel boring machine, the Seatte ground was excavated without causing instability at the surface. Merritt Ridgeley from Wisko America, Inc. took us into the tunnel to see this exciting project. At our point of entry, the tunnel expanded over a mile and a half in two directions. We were able to see Wisko using Sika Greenstreak waterproofing products up close.
Concrete segments that line the tunnel use a self-sealing gasket, but the cross-passages between the two alternating tunnels do not include these segments. Wisko is installing Sika Greenstreak Fuko hoses to waterproof the concrete barrier between the wet Seattle ground and the tunnel. The Fuko hoses are placed in a PVC geomembrane and cast into the concrete to provide a water impermeable lining. Due to the high water concentration in Seattle, the ground had to be frozen throughout the tunnel’s excavation. Merritt explained to us that after several months any leaks caused by the thawing ground will become apparent. The Fuko hose system provides a secondary water containment method by allowing Sika grout to be pumped directly into leaking areas as needed. Other Sika products are also used throughout the tunnel, including Sika Armatec 110 and Sika Repair 223.
Wisko is also currently using Sika Greenstreak products to waterproof other tunnels across the United States. Wisko is currently waterproofing Grand Central Terminal in New York City, which has more platforms that any railroad station in the world. In the ongoing Ohio River Tunnel Project, Wisko is using Sika Greenstreak to cover sections of the tunnel that are up to 120 feet across. Considering the extensive experience of Wisko, the cross-passage waterproofing project for the Seattle Light Rail is sure to go smoothly. The tunnel project is expected to be completed in 2021.