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UBC Theses and Dissertations

Elastic stress modelling and prediction of ground class using a Bayesian Belief Network at the Kemano tunnels Morgenroth, Josephine S.


The Kemano hydroelectric facility was constructed in the 1950s to supply power to the aluminum smelter in Kitimat, on the west coast of British Columbia. The Kemano project includes a 16 km long water conveyance tunnel that set world record advance rates in the 1950s, and 8 km of a partially completed tunnel. A risk management strategy was developed in the late 1980s in case of collapse of the first water conveyance tunnel, and by 1990 the excavation of a second tunnel parallel to the first had begun. Work halted in 1991 due to environmental litigation and change in political climate. In 2011 the owner of the Kitimat smelter and the Kemano hydroelectric facility announced plans to continue work on the tunnel that was left unfinished. This thesis is a collaboration with Hatch Ltd., a consultant to the owner, to determine the ground conditions and support requirements that should be anticipated in completing the backup tunnel. Three dimensional finite element elastic stress modelling was completed in order to determine the in-situ stress conditions as well as the boundary stresses around the tunnel. The modelling results were used to estimate where stress-induced problem areas should be expected, for example at chainages 10+700 to 12+700 in the backup tunnel. The results of the stress modelling were incorporated into a Bayesian Belief Network that was developed for the Kemano tunnels. It was built using widely accepted empirical relationships in rock mechanics, expert judgement and conditional relationships between inputs. This network predicts the ground class at a user-defined chainage, based on a database that was developed from project literature. The user is also able to input new data as it becomes available, for example during the tunnel advance. The predictions from the network align with what can be seen in the excavated portion of the backup tunnel, for example accurately predicting the need for steel sets at chainage 8+510. The predicted ground class was plotted as a function of chainage, and may be used as a comparison to the support requirements that have been determined thus far.

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