PSI - Issue 64

ScienceDirect Available online at www.sciencedirect.com ^ĐŝĞŶĐĞ ŝƌĞĐƚ Structural Integrity Procedia 00 (2023) 000 – 000 Available online at www.sciencedirect.com ^ĐŝĞŶĐĞ ŝƌĞĐƚ Structural Integrity Procedia 00 (2023) 000 – 000 Available online at www.sciencedirect.com Procedia Structural Integrity 64 (2024) 1636–1641

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SMAR 2024 – 7th International Conference on Smart Monitoring, Assessment and Rehabilitation of Civil Structures Enabling long-term distributed OFDR monitoring by exploiting the persistency of the Rayleigh signature Luca Schenato a, *, Martina Cappelletti a , Daniele Orsuti a , Andrea Galtarossa a , Marco Santagiustina a , Simonetta Cola b , Luca Palmieri a a Department of Information Engineering, University of Padova, Padova, I-35131, Italy. b Department of Civil, Environmental and Architectural Engineering, University of Padova, Padova I-35129, Italy. SMAR 2024 – 7th International Conference on Smart Monitoring, Assessment and Rehabilitation of Civil Structures Enabling long-term distributed OFDR monitoring by exploiting the persistency of the Rayleigh signature Luca Schenato a, *, Martina Cappelletti a , Daniele Orsuti a , Andrea Galtarossa a , Marco Santagiustina a , Simonetta Cola b , Luca Palmieri a a Department of Information Engineering, University of Padova, Padova, I-35131, Italy. b Department of Civil, Environmental and Architectural Engineering, University of Padova, Padova I-35129, Italy. Abstract Rayleigh-based distributed fiber optic sensing offers unmatched spatial resolution and accuracy among the different fiber optic techniques. With its sub-centimeter spatial resolution and microstrain accuracy over tens of meters, this technology is ideal for precise monitoring in geotechnical and civil engineering applications. This technique utilizes Rayleigh scattering to track environmental effects on light propagation, and the measurement is done through the spectral correlation analysis of the so-called Rayleigh signature, which is specific to each fiber and can be accounted for to track variation in the light propagation due to the environment. A first measurement of the Rayleigh signature is kept at the beginning of the monitoring campaign, and it is then used as a reference to determine the change in the strain or temperature field affecting the fiber. Still, measurements in installations where fibers were employed in harsh conditions have been shown only in quite favorable conditions, i.e., by using the same specific device and set up over a short time. In this work, we investigate the enduring presence of Rayleigh's signature in optical sensing fibers installed in challenging environments. In one site, the fibers were cast in the concrete of a bridge foundation pile, subject to an unremitting contraction over the years; in another site, the fibers were integrated within soil anchors subject to the action of an active landslide, which has imparted thousands of strain with marked localized strain peaks. Our study demonstrates that measurements obtained from optical fibers used in adverse conditions continue to exhibit a Rayleigh signature correlating to the reference one, even after a period exceeding five years since the initial measurements were taken and using different interrogators and setups. © 2024 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of SMAR 2024 Organizers Abstract Rayleigh-based distributed fiber optic sensing offers unmatched spatial resolution and accuracy among the different fiber optic techniques. With its sub-centimeter spatial resolution and microstrain accuracy over tens of meters, this technology is ideal for precise monitoring in geotechnical and civil engineering applications. This technique utilizes Rayleigh scattering to track environmental effects on light propagation, and the measurement is done through the spectral correlation analysis of the so-called Rayleigh signature, which is specific to each fiber and can be accounted for to track variation in the light propagation due to the environment. A first measurement of the Rayleigh signature is kept at the beginning of the monitoring campaign, and it is then used as a reference to determine the change in the strain or temperature field affecting the fiber. Still, measurements in installations where fibers were employed in harsh conditions have been shown only in quite favorable conditions, i.e., by using the same specific device and set up over a short time. In this work, we investigate the enduring presence of Rayleigh's signature in optical sensing fibers installed in challenging environments. In one site, the fibers were cast in the concrete of a bridge foundation pile, subject to an unremitting contraction over the years; in another site, the fibers were integrated within soil anchors subject to the action of an active landslide, which has imparted thousands of strain with marked localized strain peaks. Our study demonstrates that measurements obtained from optical fibers used in adverse conditions continue to exhibit a Rayleigh signature correlating to the reference one, even after a period exceeding five years since the initial measurements were taken and using different interrogators and setups. Keywords: OFDR, Rayleigh Signature, Harsh monitoring;

Keywords: OFDR, Rayleigh Signature, Harsh monitoring;

* Corresponding author. Tel.: +39-049-829-7785. E-mail address: luca.schenato@unipd.it

2452-3216 © 2024 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of SMAR 2024 Organizers 10.1016/j.prostr.2024.09.419 2452-3216 © 2024 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of SMAR 2024 Organizers 2452-3216 © 2024 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of SMAR 2024 Organizers * Corresponding author. Tel.: +39-049-829-7785. E-mail address: luca.schenato@unipd.it