2
Dam failure overview
2.1
Dam failure mechanisms
There are several possible failure modes for embankment dams, the most common ones being failure due to overtopping, piping, foundation or liquefaction. A brief description of each is provided below: — Overtopping Failure is typically the result of either an extreme storm event or a landslide within the impoundment. The flow of water over the embankment causes erosion of the downstream embankment slope material, which leads to a breach. Overtopping failure can also happen during less extreme storm events after freeboard loss due to a seismic event; spillway blockage; or it can also be caused by operating the dam at levels greater than the maximum design operating level.
An example of overtopping failure is the Zijin (China) TSF failure in 2010, which resulted in 22 deaths.
— Seepage/internal erosion (piping) is typically triggered by seepage flows concentrated along a path of high hydraulic conductivity. These seepage paths can be caused by cracking, combustion, animal activity, high hydraulic gradients, or relict structures in the foundation or embankment materials. The shear forces exerted by the escaping water can enlarge the seepage path until a portion of the embankment collapses. This results in a breach through overtopping and erosion of the caved area. A piping failure event may occur at any time and may not be a direct result of a storm event. An example of piping failure is the Cieneguita Dam (Mexico) failure in 2018. This structure was raised using the upstream method. Approximately 0.44 Mm 3 of material was released, resulting in 5 deaths. — Foundation Failure is typically the result of poor/low foundation permeability which leads to an increase in pore pressure, or excessive loading of the foundation materials. Failure potential is greater at locations where ponded water exists against an embankment face. Foundation failure can also occur due to instability in the underlying foundation, which is caused by incorrect characterisation during a structure’s design phase. Therefore, it is possible that foundation failure may occur at any location along an embankment. An example of foundation failure is the Mount Polley (Canada) TSF failure in 2014. This structure had a downstream raise construction, with approximately 23.6 Mm 3 of material (tailings and water) released. It resulted in no deaths but had a large environmental impact and clean-up effort.
Figure 2.1 presents an overview of overtopping and piping failure configurations.
Project No PS213278 Upper Mundic Gully TSF Stage 1 and 2 DBA and CCA Mount Morgan Gold Mine Heritage Minerals
WSP JUly 2025 Page 5
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