Medical Center Crossover Cavern

Washington Metropolitan Area Transportation Authority

Tunnel Waterproofing, Drainage System and Final Liner Design:

The Medical Center Metro Station, located in Bethesda, Maryland, is part of the Washington, D.C. Metro System’s Red Line. Servicing the National Institute of Health and the Walter Reed National Military Center, the station is an essential part of the Metro System.

Attached to the station is a crossover cavern structure, which consists of a rock tunnel supported with steel ribs and a shotcrete liner. This tunnel section has had extensive water intrusion since its construction in the early 1980s. Water infiltration from the surrounding rock has had impacts on various systems in the tunnel. The rehabilitation project involved the design of a new waterproofing system and final lining.

Gall Zeidler Consultants (GZ) provided expert engineering design services for the tunnel waterproofing system, the drainage system and the new final lining for the existing cavern. The new shotcrete final lining has been designed as a self-supporting structure with wire mesh as the main reinforcement. Lattice girders will be installed systematically for shape control and additional reinforcement. GZ has provided input on constructability issues for all aspects of the tunnel rehabilitation. One particular item involved the development of a detailed schedule for shotcrete delivery to the site, which included a breakdown from batching to delivery and application. Once the rehabilitation construction begins, GZ will provide resident engineering inspection services for the waterproofing, drainage, and shotcrete final lining.

Bethesda, Maryland
Crossover cavern
114 feet (35 meters)
Bedrock containing permeable (water bearing) joints and fractures, biotite-hornblende tonalite formation, high groundwater table
Gannett Fleming / Parsons JV
Washington Area Metropolitan Transportation Agency (WMATA)