WMATA Yellow Line Steel Tunnel Liner Rehabilitation

To extend the life of a section of the Washington Metro, WMATA launched the $300-million Yellow Line Tunnel Rehabilitation Project. The goal: to restore parallel 40-year-old, 3,000-ft-long tunnels and an adjacent bridge. Schnabel served as the Engineer-of-Record for the tunnel structural repair, with responsibility for performing the tunnel inspection, designing steel repairs, and developing leak mitigation measures.

This CMAR construction project was initiated to provide structural repairs to the deteriorating steel tunnel liner system. The tunnel’s existing liner consisted of about 3,000 linear feet of fabricated steel liner plates. Areas of the steel tunnel liner experienced significant corrosion and leakage over the life of the structure, which led to substantial section loss in some areas of the existing steel liner plate.

To identify tunnel areas requiring structural repair and leak mitigation, Schnabel performed a visual inspection and non-destructive UT measurements on the steel tunnel liner. The Schnabel team also implemented an instrumentation and monitoring program to evaluate vibration levels and deformations in the liner during regular train passages. Based on the data collected during inspection, our team developed a 3D structural finite element analysis to evaluate the structural integrity of the existing liner system.

In areas of heavily corroded liner plates, we designed new steel cover plate repairs, replacing the structural capacity of the existing liner system. A new corrosion protection coating system was selected to extend the service life of the tunnel liner for an additional 50 years. We also developed a leak remediation grouting program to mitigate leakage into the tunnel and limit potential future corrosion. The grouting program consisted of exterior grouting to provide an outer membrane around the steel tunnel liner, and localized joint injection grouting to reduce groundwater infiltration into the tunnel.