Stress modelling and rock support for hydro-electric water tunnels

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hydro-electric facility located 70 km southeast of Kitimat, British Columbia is an impressive feat of engineering due to both its scale and the remoteness of its location. The focus of this research are two 16 km long water conveyance tunnels, one operational and one partially complete. The first tunnel, T1, was completed in the 1950s, while T2 was partially excavated in the early 1990s. The mountainous topography in the area poses challenges for rock support design as the stresses around the tunnels vary widely along the tunnel alignment. Large variations in stress orientations and magnitudes were identified from 2D finite element stress models and these results corresponded to failure mechanisms observed on site. The proposed research has the following goals: 1) Further evaluate the expected stress conditions around the continuation of the T2 tunnel by constructing a large 3D stress analysis model covering the full length of both tunnels. 2) Incorporate predicted stresses at along the tunnel and data regarding lithology, ground water inflow, and discontinuities into a probabilistic prediction tool called a Bayesian Network. 3) Use the developed Bayesian Network tool to predict ground classes along the tunnel. 4) Use the ground classes to recommend appropriate primary and final rock support to maintain tunnel stability and in turn provide guidance on expected tunnelling costs and scheduling.