2001 – Risk and Standards Based Assessment of Internal Erosion and Piping Failure – A Convergence of Approaches

Graeme Bell, Robin Fell and Mark Foster

Standards based, dam safety management has always been about managing risks. Risk based approaches attempt to quantify the risks in a formal manner, but are based on the same requirement for good investigation and engineering, and understanding of the physical processes, as standards based methods.

This is demonstrated by the assessment of the potential for internal erosion and piping of Eucumbene Dam. The assessment is a combination of semi-quantitative risk based, and standards based approaches, and considers the likelihood of initiation, continuation, progression to form a pipe, and breach. The filter transition zones are coarser than required to meet modern filter design criteria, but it has been demonstrated by laboratory testing, and relation to the performance of other dams, that if, in the low likelihood erosion of the core initiates, it will after some erosion, seal on the filter transition zone. The downstream zone of rockfill has sufficient permeability to discharge any potential leakage which might occur, so the likelihood of breach of the dam by piping is
extremely low.