2016 – Probabilistic Slope Failure Risk Estimation of a Dam with Zones of Weak Foundation Material

Ryan Singh, Bob Wark

For existing dams built before modern theories and understanding of soil mechanics were fully developed, it was often the case that comprehensive investigations into the properties of the embankment and foundation material were not carried out. With more stringent dam safety requirements and engineering criteria, and a better understanding of soil mechanics, it is necessary to undertake embankment and foundation investigations on such dams, with the view to gain a better understanding of the embankment and foundation conditions.

This paper details the method used for a risk-based assessment of a dam’s stability against slope failure for steady-state seepage conditions, based on a probabilistic assessment of differing interpretations of the material properties for the foundation. To achieve this, several separate interpretations of material strength models were developed for a foundation, using various subsets of available tri-axial data. The mean strengths of these models were used to assess the stability, and to account for the variation in strength properties of each model, the sampling distribution of the mean was used to assess the likelihood of failure.

Finally, an event-tree type risk analysis was used to calculate a value for the probability of slope failure.

A case study has been presented using this method.

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