Probabilistic stability evaluation for wildlife-damaged earth dams: a Bayesian approach

There is a growing body of evidence confirming the detrimental effects of invasive wildlife activities on the performance and–ultimately – the safety of earth dams and levee systems. Modelling cavities and burrows dug by animals in earth structures is rather cumbersome due to their geometrical complexity and randomness. This study proposes the use of the probabilistic approach to estimate the risk associated with the presence of wildlife chambers in an arbitrary dam section. Two dimensional limit equilibrium slope stability analyses were conducted for a homogeneous silty sand dam. The animal chambers were modelled as idealised highly permeable circles with a near-zero strength. Uncertainty in the dam material was introduced using the Monte-Carlo technique to randomise the input parameters. The conditional probability of failure, P(F|C), was spatially evaluated by manual perturbations of chamber locations within the dam section. Using the Bayesian approach, the section was accordingly mapped into three stability zones: “safe”, “marginally safe” and “likely to fail” based on P(F|C) values associated with the chamber location. For this very complex problem, the probabilistic handling seems to provide a mathematically normalised basis for risk assessment in lieu of the classical belief-based single-value factor of safety (FoS).