Representation of faults and fault zones in 3D numerical stability analyses of open pit mines

Authors: Miller, AK; Peik, B; Tsai, A; Mehrabifard, A; Lawrence, K Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2535_31

Cite As:
Miller, AK, Peik, B, Tsai, A, Mehrabifard, A & Lawrence, K 2025, 'Representation of faults and fault zones in 3D numerical stability analyses of open pit mines', in JJ Potter & J Wesseloo (eds), SSIM 2025: Fourth International Slope Stability in Mining Conference, Australian Centre for Geomechanics, Perth, https://doi.org/10.36487/ACG_repo/2535_31



Abstract:
Accurate representation of faults, particularly complex fault zones, is a critical component of large-scale numerical modelling in open pit mining, where faults exert a significant influence on observed failure mechanisms and overall slope stability. This study explores the complexities associated with modelling major, heterogeneous faults and fault zones in numerical analyses for open pit mine slopes. Major faults are often characterised by a complex internal structure that extends beyond a simple planar discontinuity. They can be composed of a central core of fault gouge surrounded by zones of sheared or damaged rock of varying quality, including fault splays and lenses of weaker material distributed throughout the fault’s influence zone. Representing such faults as a single discrete plane with an assigned gouge strength may lead to oversimplified failure mechanisms as potential failure surfaces may exploit the surrounding, comparatively more competent but fractured rock or weaker pathways, such as fault splays or localised gouge accumulations within the broader fault zone. Alternatively, applying fault gouge strength across the entire damage zone of a fault would provide for conservative and economically unfavourable slope designs. To avoid such pitfalls, engineers must acknowledge and account for the heterogeneous nature of the fault zone when selecting fault geometry and material properties for numerical modelling, which requires careful consideration of the geological characteristics and potential failure pathways within the fault structure. Through a series of comparative simulations, this work evaluates the impact of fault representation in numerical models and their impact on slope stability predictions. It examines common approaches for representing faults, such as discrete interfaces, volumetric weak zones, or a fault core with associated damage zone, highlighting their respective capabilities and limitations in capturing the intricate behaviour of these geological discontinuities. The study explores the sensitivity of model results to variations in fault and damage zone representation, assumed strength parameters, and the spatial distribution of weaker materials within the fault structure. The findings, which indicate stability outcomes are critically dependent on the representation and attributes of the zone surrounding the fault, highlight the importance of developing improved structural models and using this information increases confidence in geotechnical stability analyses.

Keywords: open pit mining, slope stability, numerical modelling, fault zone representation, damage zone modelling

References: