Tailings Dam Breach Analysis

Tailings dam breach analysis of hypothetical failures supports the evaluation of potential downstream impacts, emergency preparedness and response planning, failure mitigation planning, and mine closure planning. Recognizing the complexity of actual tailings dam breach process, the Canadian Dam Association (CDA) Technical Bulletin - Tailings Dam Breach Analysis (CDA 2021) introduced four conceptual breach cases and a two-process framework for tailings dam breach analysis.

MADflow is capable of simulating the four breach cases (Cases 1A, 1B, 2A, and 2B) with implementation of the novel two-process modelling technique with distinct discharge mechanisms. The eroded tailings surface and volume are numerically modelled with temporal and spatial variations of yield stress, viscosity and specific weight of the flow mixture. Tailings mobilization modelling employs principles of critical state soil mechanics. Major hydrodynamic, geotechnical, rheological, and erodibility considerations related to the tailings hydraulic erosion, tailings mobilization, and inundation modelling are addressed. Moreover, the advanced numerical modelling not only rationalizes tailings dam breach outflow hydrography, but also provides inundation extent and other key parameters, facilitating a reasonable evaluation of the mobility of flowable tailings to support the subsequent assessment of downstream impacts.

The flow chart below illustrates the two-process modelling workflow and major components. The Process-II modelling can be an independent application to simulate discharge caused by the collapse failure mode.

Process-I involves modelling discharge of supernatant pond carrying eroded tailings and dam fills, treating the outflow mixture as a non-Newtonian fluid with variation of solids concentrations spatially and temporally during erosion (Chen 2022, Chen and Cunning 2025). The modelled breach outflow volume is coupled with the eroded tailings surface and breach geometry formation, erodibilities of the deposited tailings and dam fills, and pond volume.

Following Process-I, using the modelled tailings surface after erosion to avoid double-counting volume across phases, Process-II modelling simulates the remnant tailings as a non-Newtonian fluid from mobilization to inundation (Chen and Cunning 2021, 2025). Rheology and its relevant parameters for tailings mobilization and inundation analyses are not necessarily the same, and sometimes need to be different.

These studies underscore the critical role of tailored numerical simulations, like those facilitated by MADflow, rationalizing the tailings dam breach outflow hydrography and providing accurate prediction of flow behavior and erosion dynamics.

Tailings Dam Breach Simulation -- Process I & Process II

The video above is a synthetic example using MADflow, depicting the two-process modelling in a hypothetical tailings dam breach event. Tailings deposited behind a cross-valley dam are covered with water in the facility. The saturated tailings are susceptible to static liquefaction. One of the critical failure scenarios is the flood-induced overtopping failure (Process I), followed by discharge of liquefied tailings caused by collapse failure mode (Process II).

In the Process I modelling, the tailings surface was updated with progression of the erosion process. With intentionally exaggerated erodibility, tailings near the breach opening and the dam downstream slope are heavily eroded with deep scour by hydrodynamic force. Tailings deposit located in the far field is much less involved in the hydraulic erosion process. The hydraulic erosion process unfolds gradually over hours, reflecting its nature.

The Process-II modelling of discharge of flowable tailings resulting from the subsequent collapse failure consists of tailings mobilization and inundation analyses. This is a non-erosional failure mode; the modelling demonstrates that collapse and mobilization of liquefied tailings can occur in a very short period of time, dictated by geotechnical properties of deposited tailings and failure mechanisms. The simulated failure behavior is consistent with typical field observations of the sudden, rapid, and catastrophic nature of this type of failures.

Properties of deposited tailings may vary spatially within a tailings storage facility with different scale of variations; and can also change throughout the lifecycle of the facility. In-situ properties of deposited tailings in each tailings storage facility are unique. Taking site-specific conditions into consideration is required in a tailings dam breach analysis.