Role of the interface between distributed fibre optic strain sensor and soil in ground deformation measurement

Cheng-Cheng Zhang 1, Hong-Hu Zhu 1,2 & Bin Shi 1

1 School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China.

2 Department of Engineering, University of Cambridge, Cambridge CB2 1PZ, United Kingdom.

Correspondence and requests for materials should be addressed to H.-H.Z. 

Scientific Reports | 6:36469 | DOI: 10.1038/srep36469

Abstract Recently the distributed fibre optic strain sensing (DFOSS) technique has been applied to monitor deformations of various earth structures. However, the reliability of soil deformation measurements remains unclear. Here we present an integrated DFOSS- and photogrammetry-based study on the deformation behaviour of a soil foundation model to highlight the role of strain sensing fibre–soil interface in DFOSS-based geotechnical monitoring. Then we investigate how the fibre–soil interfacial behaviour is influenced by environmental changes, and how the strain distribution along the fibre evolves during progressive interface failure. We observe that the fibre–soil interfacial bond is tightened and the measurement range of the fibre is extended under high densities or low water contents of soil. The plastic zone gradually occupies the whole fibre length when the soil deformation accumulates. Consequently, we derive a theoretical model to simulate the fibre–soil interfacial behaviour throughout the progressive failure process, which accords well with the experimental results. On this basis, we further propose that the reliability of measured strain can be determined by estimating the stress state of the fibre–soil interface. These findings may have important implications for interpreting and evaluating fibre optic strain measurements, and implementing reliable DFOSS-based geotechnical instrumentation.




References

1. Lienhart, W. Case studies of high-sensitivity monitoring of natural and engineered slopes. J. Rock Mech. Geotech. Eng. 7, 379–384 (2015).

2. Horiguchi, T. & Tateda, M. Optical-fiber-attenuation investigation using stimulated Brillouin scattering between a pulse and a continuous wave. Opt. Lett. 14, 408–410 (1989).

3. Rogers, A. J. & Handerek, V. A. Frequency-derived distributed optical-fiber sensing: Rayleigh backscatter analysis. Appl. Opt. 31, 4091–4095 (1992).

4. Bao, X., Dhliwayo, J., Heron, N., Webb, D. J. & Jackson, D. A. Experimental and theoretical studies on a distributed temperature sensor based on Brillouin scattering. J. Lightw. Technol. 13, 1340–1348 (1995).

5. Thévenaz, L. Brillouin distributed time-domain sensing in optical fibers: State of the art and perspectives. Front. Optoelectron. China 3, 13–21 (2010).

6. Dong, Y., Chen, L. & Bao, X. Time-division multiplexing-based BOTDA over 100 km sensing length. Opt. Lett. 36, 277–279 (2011). 7. Soto, M. A., Taki, M., Bolognini, G. & Di Pasquale, F. Simplex-coded BOTDA sensor over 120-km SMF with 1-m spatial resolution assisted by optimized bidirectional Raman amplification. IEEE Photonics Technol. Lett. 24, 1823–1826 (2012).

8. Loranger, S., Gagné, M., Lambin-Iezzi, V. & Kashyap, R. Rayleigh scatter based order of magnitude increase in distributed temperature and strain sensing by simple UV exposure of optical fibre. Sci. Rep. 5, 11177 (2015).

9. Ho, Y. T., Huang, A. B. & Lee, J. T. Development of a fibre Bragg grating sensored ground movement monitoring system. Meas. Sci. Technol. 17, 1733 (2006).

10. Habel, W. R. & Krebber, K. Fiber-optic sensor applications in civil and geotechnical engineering. Photonic Sens. 1, 268–280 (2011). 

11. Iten, M. Novel applications of distributed fiber-optic sensing in geotechnical engineering. PhD thesis, Federal Institute of Technology in Zurich (2011).

12. Sun, Y. J. et al. Distributed acquisition, characterization and process analysis of multi-field information in slopes. Eng. Geol. 182, 49–62 (2014).

13. Zeni, L. et al. Brillouin optical time-domain analysis for geotechnical monitoring. J. Rock Mech. Geotech. Eng. 7, 458–462 (2015).

14. Zhu, H. H., Shi, B., Zhang, J., Yan, J. F. & Zhang, C. C. Distributed fiber optic monitoring and stability analysis of a model slope under surcharge loading. J. Mt. Sci. 11, 979–989 (2014).

15. Klar, A. et al. Distributed strain measurement for pile foundations. Proc. Inst. Civil Eng.-Geotech. Eng. 159, 135–144 (2006).

16. Lu, Y., Shi, B., Wei, G. Q., Chen, S. E. & Zhang, D. Application of a distributed optical fiber sensing technique in monitoring the stress of precast piles. Smart Mater. Struct. 21, 115011 (2012).

17. Lanticq, V. et al. Soil-embedded optical fiber sensing cable interrogated by Brillouin optical time-domain reflectometry (B-OTDR) and optical frequency-domain reflectometry (OFDR) for embedded cavity detection and sinkhole warning system Meas. Sci. Technol. 20, 034018 (2009).

18. Linker, R. & Klar, A. Detection of sinkhole formation by strain profile measurements using BOTDR: Simulation study. J. Eng. Mech. doi: 10.1061/(ASCE)EM.1943-7889.0000963 (2015).

19. Buchoud, E. et al. Quantification of submillimeter displacements by distributed optical fiber sensors. IEEE Trans. Instrum. Meas. 65, 413–422 (2016).

20. Iten, M., Puzrin, A. M. & Schmid, A. Landslide monitoring using a road-embedded optical fiber sensor. Proc. SPIE 6933, 693315 (2008).

21. Ansari, F. & Yuan, L. Mechanics of bond and interface shear transfer in optical fiber sensors. J. Eng. Mech. 124, 385–394 (1998).

22. Yuan, L. B. & Zhou, L. M. Sensitivity coefficient evaluation of an embedded fiber-optic strain sensor. Sens. Actuator A-Phys. 69, 5–11 (1998).

23. Leung, C., Wang, X. & Olson, N. Debonding and calibration shift of optical fiber sensors in concrete. J. Eng. Mech. 126, 300–307 (2000).

24. Li, H. N., Zhou, G. D., Ren, L. & Li, D. S. Strain transfer coefficient analyses for embedded fiber Bragg grating sensors in different host materials. J. Eng. Mech. 135, 1343–1353 (2009).

25. Wang, B. J., Li, K., Shi, B. & Wei, G. Q. Test on application of distributed fiber optic sensing technique into soil slope monitoring. Landslides 6, 61–68 (2009).

26. Picarelli, L. et al. Performance of slope behavior indicators in unsaturated pyroclastic soils. J. Mt. Sci. 12, 1434–1447 (2015). 

27. Zhang, C. C., Zhu, H. H., Shi, B. & She, J. K. Interfacial characterization of soil-embedded optical fiber for ground deformation measurement. Smart Mater. Struct. 23, 095022 (2014).

28. Zhang, C. C., Zhu, H. H., She, J. K., Zhang, D. & Shi, B. Quantitative evaluation of optical fiber/soil interfacial behavior and its implications for sensing fiber selection. IEEE Sens. J. 15, 3059–3067 (2015).

29. Zhu, H. H., She, J. K., Zhang, C. C. & Shi, B. Experimental study on pullout performance of sensing optical fibers in compacted sand. Measurement 73, 284–294 (2015).

30. ASTM F3079-14. Standard Practice for Use of Distributed Optical Fiber Sensing Systems for Monitoring the Impact of Ground Movements During Tunnel and Utility Construction on Existing Underground Utilities (ASTM International, West Conshohocken, PA, 2014).

31. Iten, M. et al. Study of a progressive failure in soil using BEDS. Proc. SPIE 7503, 75037S-4 (2009).

32. Suo, W. et al. Development and application of a fxed-point fber-optic sensing cable for ground fissure monitoring. J. Civ. Struct. Health Monit. 6, 715–724 (2016).

33. Stanier, S. A., Blaber, J., Take, W. A. & White, D. Improved image-based deformation measurement for geotechnical applications. Can. Geotech. J. 53, 727–739 (2016).