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Langzeitmonitoring von nicht visuell inspizierbaren Tunnelinnenschalen mittels Faseroptik
Author(s) -
Grunicke Urs H.,
Lienhart Werner,
Vorwagner Alois
Publication year - 2021
Publication title -
geomechanics and tunnelling
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.317
H-Index - 18
eISSN - 1865-7389
pISSN - 1865-7362
DOI - 10.1002/geot.202000051
Subject(s) - cladding (metalworking) , visual inspection , reliability (semiconductor) , optical fiber , structural health monitoring , computer science , structural engineering , forensic engineering , materials science , engineering , composite material , artificial intelligence , telecommunications , power (physics) , physics , quantum mechanics
Regular structural assessments of tunnel linings are commonly performed by visual inspection. Crack phenomena and their development over time are essential indicators of changes of the stress regimen. These are the most prominent input data for the structural assessment of linings. Cladding for fire protection or noise control inhibit visual inspection and call for alternative methods of crack detection and monitoring. This paper presents the application of an alternative method which employs distributed fibre optic sensing (DFOS) which is installed on already existing linings. The objective is to obtain monitoring results with best reliability in comparison to conventional inspection. While the application of DFOS with fibres embedded in new linings has already been tested extensively, later installation on existing linings poses various challenges. Based on findings obtained from laboratory and field tests in an operational highway tunnel, we found that by means of later installed fibres with lengths of up to 70 m, strain measurements can achieve accuracies of about 1 µm/m over 10 mm. This allows the detection of both current and historical crack widths at 0.01 mm precision, conspicuous strain patterns and temperature abnormalities. The system can be mounted onto the inner lining surface which is covered by later claddings and are hence inaccessible to visual inspection. The structural performance can eventually be inferred from interpreted crack patterns.