Probabilistic stability analysis of a tailings dyke on presheared clay-shale

Probabilistic slope stability analysis offers an efficient framework for logical, systematic incorporation of uncertainty into slope design. The slow integration of probabilistic slope analyses into practice is attributed, among other factors, to the lack of published studies illustrating the implementation and benefits of such techniques. A spreadsheet-based, probabilistic slope analysis methodology is applied to evaluate the stability of a section of the Syncrude Tailings Dyke in Fort McMurray, Canada. The dyke is approximately 44 m high and is founded on presheared clay-shale. The performance of the dyke is governed by uncertainties about material properties and pore-water pressures. Starting with field and laboratory data, this study demonstrates the techniques used in quantifying the various components of parameter uncertainty, conducting a probabilistic assessment, and estimating the probability of unsatisfactory performance. The probability of unsatisfactory performance of the dyke is estimated to be 1.6 x 10(-3). Field monitoring data indicate that the dyke performance is adequate. The study thus provides a first link between probability figures and performance. The analysis also quantifies the relative contributions of the various sources of uncertainty to the overall uncertainty in the factor of safety.