dic. 13, 2021

Stress-strain analysis of tailings facilities subject to dynamic loads

  • Artículo
  • Tailings Facilities
  • Dynamic Loads and Stress-strain analysis
  • Design Approach

Numerous mining-related infrastructures have been built and operated across Canada and the world, and it is a common practice to analyze the stability of their tailings facilities. However, it remains challenging to do so when they are subject to dynamic loads, including earthquakes and blasts.

Dynamic stability of tailings dams is commonly evaluated by using the pseudo-static method for low-risk regions. Such a simplified method can provide quick and cost-effective inputs. However, based on limit equilibrium analysis, it tends to oversimplify the dynamic response of tailings prone to liquefaction. In August 2020, following several recent catastrophic failures of tailings dams worldwide (e.g., Mount Polley in Canada, and Fundão and Brumadinho in Brazil), an international standard, Global Industry Standard on Tailings Management (GISTM 2020), was formulated with more stringent seismic design criteria.

In this context, BBA offers a more advanced approach, based on stress-strain (i.e., deformation) analysis, to specifically address stability problems for tailings storage facilities (TSF) that are subject to dynamic loads.

  1. 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.

    To learn more, please contact us.

This content is for general information purposes only. All rights reserved ©BBA

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