PSI - Issue 64

Łukasz Bednarski et al. / Procedia Structural Integrity 64 (2024) 1681 – 1688 Author name / Structural Integrity Procedia 00 (2019) 000-000

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Fig. 3. Examples of applications of monolithic DFOS sensors in Poland: a) sewage collector; b) high-pressure gas pipeline; c) concrete highway section; d) composite-concrete footbridge; e) steel bridge; f) road embankment; g) asphalt road layers; g) prestressed concrete girders; h) experimental railway embankment section. 2. Distributed sensing of rail deformation This chapter discusses selected aspects of the DFOS system designed and implemented to monitor rail deformation. The project was implemented in the Świętokrzyskie region, Poland, and the first measurements were made in early 2023. The total length of the installed monolithic sensors is 2200 m, making this system probably the largest of its kind in the world. The objective of the system is to carry out simultaneous measurements of axial strain, temperature, curvature and vertical displacement in long-term as well as short-term dynamic measurements during train passages. The following DFOS measurement techniques were used: • DSS - distributed strain sensing, • DTS - distributed temperature sensing, • DDS - distributed displacement sensing, • DAS - distributed acoustic sensing (vibration/strain rate sensing). The DFOS system is supported by automatic bidirectional tiltmeters spaced every 25 m along the monitored section, and inclinometers spaced every 100 m for manual measurements of horizontal displacements - Figure 4.

Fig. 4. Example section of the embankment with DFOS sensors, automatic tiltmeters and manual inclinometers – top view.

Two DFOS sensors were installed on the rail web: the upper one (below the rail head) and the lower one (above the foot) - Figures 5a (scheme) and 5b (implementation). The sensors were continuously bonded to the cleaned rail surface using a suitable adhesive whose mechanical parameters (including adhesion) had been previously verified in laboratory tests on a testing machine.