Improving tunnel resilience against fires: A new methodology based on temperature monitoring

• Temperature monitoring is critical for increasing tunnel resilience.
• A methodology for the optimal design of temperature monitoring systems is presented.
• The methodology is applied to the Virgolo Tunnel.
• Results show that proper location of the temperature sensors is crucial.
• Monitored tunnel sections should have at least three sensors.

Monitoring temperatures during tunnel fires is of major importance for both the firefighters extinguishing the fire, and the engineers in charge of the subsequent repair work. However, current methods of assessing fire damage have limitations when applied to tunnels and only provide estimates of the maximum fire temperatures at specific locations of the tunnel. This is not a desirable situation, as the temperature–time curves associated with the fire event should be available for use in assessing the residual strength of the tunnel structure. This is the key parameter in defining repair work and the length of time the tunnel will need to be closed and thus the socio-economic cost of the tunnel fire. In addition, real-time recording of the temperature–time curves would provide valuable information to the firefighters engaged in extinguishing the fire.This paper presents a new general methodology for the optimal placement of sensors in a tunnel to obtain the temperature evolution at any point along its lining during a fire. The methodology was applied to the Virgolo Tunnel in Italy, in which 100 potential high-temperature sensor configurations were tested and a set of optimal sensor configurations was proposed. The results of the analysis show that: (a) the proper location of the sensors is crucial; (b) it is possible to define a set of sensor configurations that minimize the cost of the monitoring system and maximize the accuracy of the estimated temperatures; (c) it is important to place at least three high-temperature sensors in each monitored cross section (at the crown and symmetrically on the haunches/side walls). The proposed methodology improves tunnel resilience against fires, as it enables safer infrastructure and a faster and more economic recovery of the tunnel after a fire event.

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