Traditional technologies are not adequate for permanent monitoring of long tunnels, also cause they need an a-prori knowledge of the structure.

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A distributed optical fiber monitoring system is, instead, very suitable for the monitoring of tunnels, expecially mile-long ones.

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With a proper installation, a single fiber allows to perform a continuous monitoring, with an high spatial resolution, up to distances of some tens of kilometres, where strain (longitudinal and transverse) profile allows to detect the formation of any cracks in the lining. 

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This enables to avoid a priori selecting the part, considered critical, to monitor as in the more traditional approach.