The Canarsie Tunnel, along the L-Line of New York subway network, links Manhattan with Brooklyn. The tunnel was flooded in 2012 during Hurricane Sandy, resulting in damage to electrical cables and the concrete duct banks. The initial refurbishing plans called for a complete closure of the tunnel for 18 months to replace the duct banks and cables, causing significant disruption to L-Train commuters.
Governor Cuomo encouraged MTS to consider innovative alternatives to maintain service during repairs. With the support of Cornell and Columbia University experts, an alternative plan was adopted implementing a new racking system for the power cables and leaving the original benchwall in place where structurally stable. Short sections of the benchwall were demolished and other reinforced in fiber reinforced polymers.
As an additional safety measure distributed “Smart” optical fiber sensor cables were installed long the remaining benchwall to detect and localize future shifts and cracks. MTA selected Smartec and Roctest to supply and implement this advanced fiber optic monitoring system.
The rehabilitation project was completed in June 2020 with Governor Andrew Cuomo announcing: “New data-driven and preventative approach to monitoring tunnel resiliency: The new fiber optic monitoring system, installed along the entire wall of the tunnel including the new FRP and existing concrete, uses a total of 14,000 feet of specialized hydro- and geo-sensing fiber optic cables that report any movement of the tunnel wall instantly. The data is directly sent to the Rail Control Center, where it is continuously monitored by a dedicated team for patterns and who can respond to any issues in real-time.”
The measurements are performed using SMARTEC’s Hydro & Geo sensing cable with a total length of more than 4’000m, covering both duct banks in the two parallel tunnels. The measurement cabinet includes redundant DiTeSt distributed strain sensing systems combined with DiTemp temperature sensing interrogators. The DiView data management system combines information from both systems to analyze strain and temperature variations in the two tunnels and displays the results in a single user interface. Alerts can be set based on different conditions for strain and temperature variations and enable easy localization of the triggering events.