Stress-strain analysis of tailings facilities subject to dynamic loads

Approach

Rationale

The Canadian mining industry strives to achieve zero harm to people and the environment, which in turn requires practitioners to prioritize TSF safety throughout the life cycle.

When TSFs are composed of materials susceptible to liquefaction, various regulations do not recommend the simplified pseudo-static analysis method. It is strongly suggested to analyze TSF seismic performance using a different approach. Due to the high safety requirements and uncertainties associated with TSFs, more and more Canadian mines have adopted stress-strain analysis to ensure TSF safety during operation, closure and post-closure.

Geotechnical inputs

Geotechnical investigations, including standard penetration testing (SPT) and seismic cone penetration testing (SCPT), are required to provide the necessary geomechanical properties for deposited tailings and foundation soils. The advantage of stress-strain analysis is that it more fully incorporates structural material properties, thus, simulating the behaviour of the structure in a more realistic manner.

Dynamic inputs

Another critical task is to develop site design earthquakes (ground motions) from the average seismic hazard disaggregation data that corresponds to a certain dam classification and annual exceedance probability. In general, the goal is to modify ground motions selected from a representative database so their spectral responses and other characteristics could reasonably match that of the design target over the frequency range of interest.

Modelling procedure

Stress-strain analysis is carried out in four (4) main steps with Fast Lagrangian Analysis of Continua (FLAC) or similar codes:

• Step 1: Establish the in-situ loading conditions.
• Step 2: Reach the static equilibrium state with the simulated liquefied materials.
• Step 3: Apply design earthquakes to models to analyze the dynamic response of structure.
• Step 4: Continue running post-liquefied models in static conditions.

Advantages

The main advantages offered by stress-strain analysis include:

• Advanced constitutive models better representing liquefiable tailings
• Visualization of the evolution of stress state, deformations, pore water pressures and liquefaction of tailings
• Capable of running post-seismic (or post-liquefied) stability analysis

Conclusion

Previous academic and practical studies have indicated that the dynamic TSF response can be better addressed by advanced stress-strain analysis, particularly for liquefiable tailings. This method, compared to the pseudo-static method, can simulate the dynamic response of tailings facilities and reproduce key elements, including the evolution of stress state, deformations and pore water pressures during and after dynamic events. Therefore, it would certainly provide valuable design inputs and aid in the decision-making process.

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