Feasibility study of strain based stability evaluation of locally loaded slopes: insights from physical and numerical modeling

Hong-Hu Zhu 1, Zheng-Yu Wang 1, Bin Shi 1, John Kam-Wing Wong 2

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

2. Department of Engineering, University of Cambridge, Cambridge, United Kingdom

Engineering Geology, 2016. DOI: 10.1016/j.enggeo.2016.04.019

Abstract: Distributed strain monitoring of geotechnical structures has gained increasing attention in the past decade. The distributed fiber optic strain sensing (DFOSS) technology enables the measurement of strain distribution in soil slopes. This paper aims to investigate the feasibility of strain based slope stability evaluation for locally loaded slopes. The measurements of horizontal strains at different elevations in a two-dimensional (2D) model slope subjected to a vertical surcharge load were analyzed. Empirical relationships between different types of strain parameters and factors of safety calculated by the conventional method were established. To verify the above findings, a 2D finite element model of a homogeneous soil slope was built. By applying a gradually increasing local load on the numerical model, the strains in the soil mass and eventually slope failure were induced. The strain distributions of several virtual monitoring lines under different loading levels were captured and analyzed in detail. At the same time, the strength reduction method (SRM) was used to perform slope stability analysis. The results show that the strain distribution characteristics are closely related to the propagation of plastic zones and the formation of the critical slip surface. Taking into consideration the convenience of field instrumentation and monitoring sensitivity, the maximum strains at different elevations can be used as characteristic parameters for estimating the slope stability condition. Compared with conventional displacement based slope stability evaluation method, the proposed methodology is more efficient and sensitive, which makes full use of the benefits of the DFOSS technology. 

Keywords: slope stability; distributed geotechnical monitoring, strain distribution; factor of safety; numerical analysis


References

  • Bishop, A.W., 1955. The use of the slip circle in the stability analysis of slopes. Géotechnique 5, 7–17.
  • Cheng, Y.M., Lansivaara, T., Wei, W.B., 2007. Two-dimensional slope stability analysis by limit equilibrium and strength reduction methods. Comput. Geotech. 34, 137–150.
  • Cheuk, C.Y., Ng, C.W.W., Sun, H.W., 2005. Numerical experiments of soil nails in loose fill slopes subjected to rainfall infiltration effects. Comput. Geotech. 32, 290–303.
  • Crosta, G.B., Agliardi, F., 2003. Failure forecast for large rock slides by surface displacement measurements. Can. Geotech. J. 40, 176–191.
  • Di Maio, C., Vassallo, R., Vallario M., 2013. Plastic and viscous shear displacements of a deep and very slow landslide in stiff clay formation. Eng. Geol. 162, 53–66.
  • Griffiths, D.V., Lane, P.A., 1999. Slope stability analysis by finite elements. Geotechnique 49, 387–403.
  • Hanna, T.H., 1985. Field Instrumentation in Geotechnical Engineering. Trans Tech Publications, Clausthal-Zellerfeld, Germany.
  • Huntley, D., Bobrowsky, P., Zhang, Q., Sladen, W., Bunce, C., Edwards, T., Hendry, M., Martin, D., Choi, E., 2014. Fiber optic strain monitoring and evaluation of a slow-moving landslide near Ashcroft, British Columbia, Canada. In: Sassa, K., Canuti, P., Yin, Y.P. (Eds.), Landslide Science for a Safer Geoenvironment - Volume 1, pp. 415–421.
  • Intrieri, E., Gigli, G., Mugnai, F., Fanti, R., Casagli, N., 2012. Design and implementation of a landslide early warning system. Eng. Geol. 147–148, 124–136.
  • Iten, M., 2011. Novel application of distributed fiber-optic sensing in geotechnical engineering. PhD Thesis, EPFL, Switzerland.
  • Keskin, M.S., Laman M., 2013. Model studies of bearing capacity of strip footing on sand slope. KSCE J. Civ. Eng. 17, 699–711.
  • Li, D.Y., Yin, K.L., Leo, C., 2010. Analysis of Baishuihe landslide influenced by the effects of reservoir water and rainfall. Environ. Earth Sci. 60, 677–687.
  • Li, N., Cheng, Y.M., 2015. Laboratory and 3-D distinct element analysis of the failure mechanism of a slope under external surcharge. Nat. Hazards Earth Syst. Sci. 15, 35–43.
  • Lienhart, W., 2015. Case studies of high-sensitivity monitoring of natural and engineered slopes. J. Rock Mech. Geotech. Eng. 7, 379–384.
  • Liu, D., Chen, X.P., 2015. Shearing characteristics of slip zone soils and strain localization analysis of a landslide. Geomech. Eng. 8, 33–52.
  • Liu, S.L., Zhang, D., Zhang, P.S., Wang, J.C., Shi, B., 2014. Deformation monitoring of overburden based on distributed optical fiber sensing technology. Proc. 5th Intl. Forum on Opto-electronic Sensor-based Monitoring in Geo-engineering, Nanjing, China, pp. 132–135.
  • Massey, C.I., Petley, D.N., McSaveney, M.J., 2013. Patterns of movement in reactivated landslides. Eng. Geol. 159, 1–19.
  • Mohamad, H., Soga, K., Bennett, P.J., Mair, R.J., Lim, C.S., 2012. Monitoring twin tunnel interaction using distributed optical fiber strain measurements. J. Geotech. Geoenviron. Eng. 138, 957–967.
  • Pantelidis, L., Griffiths, D.V., 2015. Footing on the crest of slope: slope stability or bearing capacity? In: Lollino, G., Giordan, D., Crosta, G., Corominas, J., Azzam, R., Wasowski, J., Sciarra, N. (Eds.), Engineering Geology for Society and Territory - Volume 2, pp. 1231–1234.
  • Plaxis (2002). User manual, 2D version8 (Edited by Brinkgreeve, R.J.B.), Delft University of Technology & PLAXIS b.v., The Netherlands.
  • Shiau, J., Merifield, R., Lyamin, A., Sloan, S., 2011. Undrained stability of footings on slopes. Int. J. Geomech. 11, 381–390.
  • Stark, T.D., Choi, H., 2008. Slope inclinometers for landslides. Landslides 5, 339–350.
  • Su, M.B., Liao, C.H., 2006. Application of TDR cables for landslide monitoring. Proc. TDR 2006, Purdue University, West Lafayette, USA, no. 12.
  • Sun, Y.J., Zhang, D., Shi, B., Tong, H.J., Wei, G.Q., Wang, X., 2014. Distributed acquisition, characterization and process analysis of multi-field information in slopes. Eng. Geol. 182A, 49–62.
  • 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.
  • Xu, Q., Yuan, Y., Zeng, Y.P., Hack, R., 2011. Some new pre-warning criteria for creep slope failure. Sci. China Ser. E. Technol. Sci. 54, 210-220.
  • Xue, L., Qin, S.Q., Li, P., Li, G.L., Oyediran, I.A., Pan, X.H., 2014. New quantitative displacement criteria for slope deformation process: From the onset of the accelerating creep to brittle rupture and final failure. Eng. Geol. 182A, 79–87.
  • Yang, X.L., Wang, Z.B., Zou, J.F., Li, L., 2007. Bearing capacity of foundation on slope determined by energy dissipation method and model experiments. J. Cent. South Univ. Technol. 14, 125–128.
  • Yin, Y., Wang, H., Gao, Y., Li, X., 2010. Real-time monitoring and early warning of landslides at relocated Wushan town, the three gorges reservoir, China. Landslides 7, 339–349.
  • Yu, Y., Shang, Y.Q., Sun, H.Y., Wang, E.Z., 2015. Displacement evolution of a creeping landslide stabilized with piles. Nat. Hazards 75, 1959–1976.
  • Yu, Y., Wang, E.Z., Zhong, J.W., Liu, X.L., Li, P.H., Shi, M., Zhang, Z.G., 2014. Stability analysis of abutment slopes based on long-term monitoring and numerical simulation. Eng. Geol. 183, 159–169.
  • Zeng, X., Bao, X., Chhoa, C.Y., Bremner, T.W., Brown, A.W., DeMerchant, M.D., Ferrier, G., Kalamkarov, A.L., Georgiades, A.V., 2002. Strain measurement in a concrete beam by use of the Brillouin-scattering-based distributed fiber sensor with single-mode fibers embedded in glass fiber reinforced polymer rods and bonded to steel reinforcing bars. Appl. Optics 41, 5105–5114.
  • Zhou, W.H., Yin, J.H., Hong, C.Y., 2011. Finite element modelling of pullout testing on a soil nail in a pullout box under different overburden and grouting pressures. Can. Geotech. J. 48, 557–567.
  • Zhu, H.H., Shi, B., Yan, J.F., Zhang, J., Wang, J., 2015. Investigation of the evolutionary process of a reinforced model slope using a fiber-optic monitoring network. Eng. Geol. 186, 34–43.
  • 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.
  • Zienkiewicz, O.C., Humpheson, C., Lewis, R.W., 1975. Associated and non-associated visco-plasticity and plasticity in soil mechanics. Geotechnique 25, 671–689.