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UBC Theses and Dissertations

Investigation of rock slope deformation at the Wahleach Hydroelectric Project using the Flac computer code Stewart, Thomas W.G.


Progressive deformation of the large natural rock slope at British Columbia Hydro's Wahleach hydroelectric project is an ongoing phenomenon. Slope movements have caused significant operational problems in the original power tunnels located within portions of the deforming slope, and pose a recognized hazard to property and facilities located at the base of the slope. Developing a more comprehensive understanding of the rock slope deformation mechanics has been fundamental in evaluating the potential risk to facilities located at the base of the slope. This has been achieved through an extensive investigation and monitoring program, and supported by detailed numerical modelling studies presented in this report. Numerical modelling with the finite difference FLAC computer code has utilized the extensive slope monitoring history developed between 1989 and 1994 to evaluate the model response. This has allowed the model to be used to evaluate the possible failure modes in the slope and to investigate the effects of future loading conditions such as earthquakes and extreme precipitation events, in addition to the potential long term evolution of the slope movement process. Application of the FLAC code enabled a representative simulation of observed slope conditions to be made. Modelling results yielded excellent comparison with slope instrumentation data, developing confidence in the modelling capabilities to carry out predictive analyses of potential future loading conditions. The modelling indicated the importance of transient groundwater flow to the deformation process in the upper 40 to 70 metres of the rock mass. B.C. Hydro recognized the potentially critical impact of adverse slope movement on the collection of hydroelectric, transportation and communication facilities located at the base of the Wahleach slope. Comprehensive investigative work, undertaken following the rupture of the steel lining of the power conduit, concluded that the nature of the slope movements indicated that a rapid failure mechanism was unlikely to develop. The modelling studies described herein provided further support that rapid slope failure is unlikely. Moreover, the numerical modelling provided important insight into the slope deformation mechanics, enhancing the understanding of this regionally important phenomenon.

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