Investigation Of The Evolutionary Process Of A Reinforced Model Slope Using A Fiber-Optic Monitoring Network

Hong-Hu Zhu, Bin Shi, Jun-Fan Yan, Jie Zhang, Jing Wang

School of Earth Sciences and Engineering, Nanjing University, Nanjing, China

Department of Geotechnical Engineering, Tongji University, Shanghai 200092, China

School of Control Science and Engineering, Shandong University, Jinan 250061, China

DOI: 10.1016/j.enggeo.2014.10.012

ABSTRACT: The stability condition of a reinforced slope is influenced by many factors, such as surface loading, adjacent excavation, groundwater seepage, rainfall infiltration, and earthquake, etc. In order to investigate the evolution of stability condition of a soil slope reinforced with soil nails, a physical model test at 1 g condition was conducted in laboratory. In the model test, an innovative quasi-distributed fiber-optic sensing network based on the fiber Bragg grating (FBG) technology was developed to monitor the strain distributions of the soil nails, the slope subsurface displacements, and the internal strains of the soil mass, together with laser displacement transducers for surface displacement measurement. The sensor installation and temperature compensation methods of the monitoring system were presented in detail. During testing, the surcharge loading was applied on the slope crest in stages using hydraulic jacks and the slope behavior was carefully monitored. The simplified Bishop’s method was performed beforehand to obtain the factors of safety and the critical slip surfaces of the model slope. It is found that the measured strains of the model soil nails had a close relationship with loading magnitudes. The bending stiffness of the model soil nails contributed to the stability of the model slope when considerably large deformation occurred. The variation of slope movements and the distribution pattern of internal strains in the active and passive zones were further discussed, which indicates the progressive evolutionary process of the reinforced slope. It is verified that the fiber-optic monitoring data can identify the evolutionary stages of a reinforced slope effectively.

Keywords: slope stability; fiber-optic sensor; fiber Bragg grating (FBG); soil nailing; factor of safety; strain monitoring

References

Bishop, A.W., 1955. The use of the slip circle in the stability analysis of slopes. Géotechnique 5, 7–17.

Bozzano, F., Bretschneider, A., Martino, S., Prestininzi, A., 2014. Time variations of the K0 coefficient in overconsolidated clays due to morphological evolution of slopes. Eng. Geol. 169, 69–79.

Chen, R.H., Kuo, K.J., Chen, Y.N., Ku, C.W., 2011. Model tests for studying the failure mechanism of dry granular soil slopes. Eng. Geol. 119, 51–63.

Costa, A.D., Sagaseta, C., 2010. Analysis of shallow instabilities in soil slopes reinforced with nailed steel wire meshes. Eng. Geol. 113, 53–61.

Deepa, V., Viswanadhamt, B.V.S., 2009. Centrifuge model tests on soil-nailed slopes subjected to seepage. Ground Improvement 162, 133–144.

Dunnicliff, J., 1993. Geotechnical Instrumentation for Monitoring Field Performance. John Wiley & Sons, Inc., New York.

GEO-SLOPE, 2008. Stability Modeling with SLOPE/W 2007, an Engineering Methodology, Third Edition.

Giri, D., Sengupta, A., 2009. Dynamic behavior of small scale nailed soil slopes. Geotech. Geol. Eng. 27, 687–698.

Habel, W.R., Krebber, K., Dantan, N., Schallert, M., Hofmann, D., 2007. Recent examples of applied fibre optic sensors in geotechnical areas to evaluate and monitor structural integrity. Proc of 2nd Intl. Workshop on Opto-electronic Sensor-Based Monitoring in Geo-engineering, Nanjing, China, pp. 27–35.

Hill, K.O., Fujii, Y., Johnson, D.C., Kawasaki, B.S., 1978. Photosensitivity in optical fiber waveguides: application to reflection filter fabrication. Appl. Phys. Lett. 32, 647–649.

Ho, Y.T., Huang, A.B., Lee, J.T., 2006. Development of a fibre Bragg grating sensored ground movement monitoring system. Meas. Sci. Technol. 17, 1733−1740.

Hong, Y.S., Chen, R.H., Wu C.S., Chen J.R., 2005. Shaking table tests and stability analysis of steep nailed slopes. Can. Geotech. J. 42, 1264–1279.

Huang, A.B., Lee, J.T., Ho, Y.T., Chiu, Y.F., Cheng, S.Y., 2012. Stability monitoring of rainfall induced deep landslides through pore pressure profile measurements Soils Found. 52, 737–747.

Iten, M., 2011. Novel application of distributed fiber-optic sensing in geotechnical engineering. PhD Thesis, EPFL, Switzerland.

Jia, G.W., Zhan, T.L.T., Chen, Y.M., Fredlund, D.G., 2009. Performance of a large-scale slope model subjected to rising and lowering water levels. Eng. Geol. 106, 92–103.

Kim, D.S., Juran, I., Nasimov, R., Drabkin, S., 1995. Model study on the failure mechanism of soil-nailed structure under surcharge loading. Geotech. Test. J. 18, 421–430.

Liu, J., Wang, G., Kamai, T., Zhang, F.Y., Shi, B. 2011. Liquefaction behaviour of saturated fiber-reinforced sand in undrained ring-shear tests. Geotext. Geomembranes 29, 98-107.

Morey, W.W., Meltz, G., Glenn, W.H.G., 1989. Fiber optic Bragg grating sensors. Proc. SPIE, 1169, pp. 98–107.

Orense, R.P., Shimoma, S., 2004. Instrumented model slope failure due to water seepage. J. Nat. Disaster Sci. 26, 15–26.

Othonos, A., Kalli, K., 1999. Fiber Bragg Gratings: Fundamentals and Applications in Telecommunications and Sensing. Artech House, London.

Pei, H.F., Cui, P., Yin, J.H., Zhu, H.H., Chen, X.Q., Pei, L.Z., Xu, D.S., 2011. Monitoring and warning of landslides and debris flows using an optical fiber sensor technology. J. Mt. Sci. 8, 728–738.

Qin, S., Jian, J.J., Wang, S., Long, H., 2001. A nonlinear catastrophe model of instability of planar-slip slope and chaotic dynamical mechanisms of its evolutionary process. Int. J. Solids Struct. 38, 8093–8109.

Sasahara, K., Sakai, N., 2014. Development of shear deformation due to the increase of pore pressure in a sandy model slope during rainfall. Eng. Geol. 170, 43–51.

Tei, K., Taylor, R.N., Milligan, G.W.E., 1998. Centrifuge model tests of nailed soil slopes. Soils Found. 38, 165–177.

Tufenkjian, M.R., Vucetic, M., 2000. Dynamic failure mechanism of soil-nailed excavation models in centrifuge. J. Geotech. Geoenviron. Eng. 126, 227–235.

Turner, J.P., Jensen, W.G., 2005. Landslide stabilization using soil nail and mechanically stabilized earth walls: case study. J. Geotech. Geoenviron. Eng. 131, 141–150.

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

Zhang, J., Pu. J., Zhang, M., Qiu, T., 2001. Model tests by centrifuge of soil nail reinforcements. J. Test. Eval. 29, 315–328.

Zhu, H.H., Ho, A.N.L., Yin, J.H., Sun, H.W., Pei, H.F., Hong, C.Y., 2012. An optical fibre monitoring system for evaluating the performance of a soil nailed slope. Smart Struct. Syst. 9, 393–410.

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

Zhu, H.H., Yin, J.H., Yeung, A.T., Jin, W., 2011. Field pullout testing and performance evaluation of GFRP soil nails. J. Geotech. Geoenviron. Eng. 137, 633–641.

Zhu, H.H., Yin, J.H., Zhang, L., Jin, W., Dong J.H., 2010a. Monitoring internal displacements of a model dam using FBG sensing bars. Adv Struct. Eng. 13, 249–261.

Zhu, W.S., Zhang, Q.B., Zhu, H.H., Li, Y., Yin, J.H., Li, S.C., Sun, L.F., Zhang, L., 2010b. Large-scale geomechanical model testing of an underground cavern group in a true three-dimensional (3D) stress state. Can. Geotech. J. 47, 935–946.