Canarsie Tunnel Retrofit

Description

The L Train carries about 400,000 passengers daily under the East River between Brooklyn and Manhattan using the Canarsie tunnels. The tunnels were heavily damaged by flooding from Superstorm Sandy. The concrete bench walls that housed the conduit and embedded cables had started to crumble and fall on to the tracks.

The original bench repair plan called for demolishing and rebuilding the concrete bench walls which would have shut down the L Train for nearly 18 months disrupting service to thousands. Governor Cuomo asked the engineering faculty from Cornell and Columbia to suggest alternate options that would keep the tunnel open. The faculty recommended abandoning the embedded cables and coating the concrete benches with an FRP strengthening system, a well known technique used for upgrading concrete structures.

When WSP reached out to Gregg Blaszak – an expert in FRP strengthening – to discuss the proposed FRP option, he offered a variation on the concept proposed by academia that could more easily and quickly be implemented in the tunnel. For an FRP strengthening system to work, it needs to be well adhered to the concrete, which would have required significant concrete repairs and surface preparation. While the FRP strengthening system can quickly be installed, the surface preparation would be time consuming and expensive. Blaszak suggested using a pre-fabricated FRP shroud that could be bolted to the tunnel walls, enabling long sections of the deteriorated bench wall to be encased during the nights to limit disruption to the daytime train service. Composite Advantage built prototype shrouds to demonstrate the technique and ultimately supplied the shrouds for the tunnel.

The project was completed in 12 months, 6 months ahead of the original total shutdown proposal, and saved nearly $100 million dollars. Coastline is proud to have helped move the FRP repair concept to practice.