An optical fibre monitoring system for evaluating the performance of a soil nailed slope

Hong-Hu Zhu*1 , Albert N. L. Ho2 , Jian-Hua Yin3 , H. W. Sun4 , Hua-Fu Pei3  and Cheng-Yu Hong3
1. School of Earth Sciences and Engineering, Nanjing University, Nanjing 210093, China
2. Ove Arup & Partners Hong Kong Limited, Hong Kong, China
3. Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China
4. Geotechnical Engineering Office, Civil Engineering and Development Department, Government of the Hong Kong Special Administrative Region, Hong Kong, China 

SOURCE Smart Structures and Systems, Volume 9, Number 5, May 2012

Conventional geotechnical instrumentation techniques available for monitoring of slopes, especially soil-nailed slopes have limitations such as electromagnetic interference, low accuracy, poor longterm reliability and difficulty in mounting a series of strain sensors on a soil nail bar with a small-diameter. This paper presents a slope monitoring system based on fibre Bragg grating (FBG) sensing technology. This monitoring system is designed to perform long-term monitoring of slope movements, strains along soil nails, and other slope reinforcement elements. All these FBG sensors are fabricated and calibrated in laboratory and a trial of this monitoring system has been successfully conducted on a roadside slope in Hong Kong. As part of the slope stability improvement works, soil nails and a toe support soldier-pile wall were constructed. During the slope works, more than 100 FBG sensors were installed on a soil nail, a soldier pile, and an in- place inclinometer. The paper presents the layout and arrangement of the instruments as well as the installation procedures adopted. Monitoring data have been collected since March 2008. This trial has demonstrated the great potential of the optical fibre monitoring system for long-term monitoring of slope performance. The advantages of the slope monitoring system and experience gained in the field implementation are also discussed in the paper.

Key Words
optical fibre sensing; soil nailing; slope monitoring system; fibre Bragg grating (FBG); geotechnical instrumentation


  • Ding, X. -L., Huang, D. -F., Yin, J. -H., Chen, Y. -Q., Lau, C. K., Yang, Y. -W., Sun, Y. -R., Chen, W. and He, X. -F. (2003), “Development and field testing of a multi-antenna GPS system for deformation monitoring”, Wuhan Univ. J. Nat. Sci., 8(2), 671-676.
  • Dunnicliff, J. (1993), Geotechnical Instrumentation for Monitoring Field Performance, John Wiley & Sons Inc, New York.
  • Fredlund, D. G. and Rahardjo, H. (1993), Soil Mechanics for Unsaturated Soils, John Wiley & Sons Inc, New York.
  • Kersey, A. D., Davis, M. A., Patrick, H. J., LeBlanc, M., Koo, K. P. Askins, C. G., Putnam, M. A. and Friebele, E. J. (1997), “Fiber grating sensors”, J. Lightwave Technol., 15(8), 1442-1463.
  • Gasmo, J., Hritzuk, K. J., Rahardjo, H. and Leong, E. C. (1999), “Instrumentation of an unsaturated residual soil slope”, Geotech. Test. J., 22(2), 128-137.
  • Hill, K. O., Fujii, Y., Johnson, D. C. and Kawasaki, B. S. (1978), “Photosensitivity in optical fiber waveguides: application to reflection filter fabrication”, Appl. Phys. Lett., 32(10), 647-649.
  • Ho, Y. T., Huang, A. B. and Lee, J. T. (2006), “Development of a fibre Bragg grating sensored ground movement monitoring system”, Meas. Sci. Technol., 17(7), 1733-1740.
  • Inaudi, D. (1997), Fiber Optic Sensor Network for the Monitoring of Civil Engineering Structures, PhD Thesis, EPFL, Lausanne, Switzerland.
  • Li, A. G., Yue, Z. Q., Tham, L. G., Lee, C. F. and Law, K. T. (2005), “Field-monitored variations of soil moisture and matric suction in a saprolite slope”, Can. Geotech. J., 42(1), 13-26.
  • Lin, C. P. and Tang, S. H. (2005). “Development and calibration of a TDR extensometer for geotechnical monitoring”, Geotech. Test. J., 28(5), 1-8.
  • Millis, S. W., Ho, A. N. L., Chan, E. K. K., Lau, K. W. K. and Sun, H. W. (2008), “Instrumentation and real time monitoring of slope movement in Hong Kong”, Proceedings of 12th International Conference of International Association for Computer Methods and Advances in Geomechanics, Goa, India, 4563-4576.
  • Morey, W. W., Meltz, G. and Glenn, W. H. (1989), “Fiber Optic Bragg Grating sensors”, Proceedings of SPIE, 1169, 98-107.
  • Ng, C. W. W., Zhan, L. T., Bao, C. G., Fredlund, D. G. and Gong, B. W. (2003), “Performance of an unsaturated expansive soil slope subjected to artificial rainfall infiltration”, Geotechnique, 53(2), 143-157.
  • Peyret, M., Djamour, Y., Rizza, M., Ritz, J. F., Hurtrez, J. E. , Goudarzi, M. A., Nankali, H., Chéry, J., Le Dortz, K. and Uri, F. (2008), “Monitoring of the large slow Kahrod landslide in Alborz mountain range (Iran) by GPS and SAR interferometry”, Eng. Geol., 100(3-4), 131-141.
  • Wong, H. N., Ho, K. K. S. and Sun, H. W. (2006), “The role of slope instrumentation in landslide risk management-Hong Kong experience”, Proceedings of the Conference on Landslide, Sinkhole, Ipoh, Malaysia, 1-33.
  • Yin, J. H., Ding, X. L., Yang, Y. W., Lau, C. K., Huang, D. F. and Chen, Y. Q. (2004). “Integration of conventional instruments and global positioning system for automatic monitoring of slopes”, Chin. J. Rock Mech. Eng., 23(3), 357-364. (in Chinese)
  • Yoshida, Y., Kashiwai, Y., Murakami, E., Ishida, S. and Hashiguchi, N. (2002), “Development of the monitoring system for slope deformations with fiber Bragg grating arrays”, Proceedings of SPIE, 4694, 296-303.
  • Zhang, T. L. T., Ng, C. W. W. and Fredlund, D. G. (2006), “Instrumentation of an unsaturated expansive soil slope”, Geotech. Test. J., 30(2), 1-11.

Fulltext Link: