A methodology to evaluate the impact of major geological faults on the stability of backs in open stopes using DEM

Abstract

Since the introduction of the original Stability Graph Method by Mathews et al. in 1981, its use has been widely extended in underground mining of Sublevel Open Stoping (SLS). However, the methodology is restrictive because objectively represents an applicable tool only for similar conditions to the case histories (data) where it was calibrated (site-specific conditions). In addition, and not less important, the stability graph methodology does not contemplate in its analysis the major geological structures but assesses the incidence of minor discontinuities, leaving aside one of the main reasons associated to the unplanned dilution due to overbreak, the faults. Therefore, is important to determine the influence of major geological faults in the design of open stopes and their direct impact in the information for mining design and planning. The main objective of this thesis is to calibrate and verify a criterion that allows an evaluation of the impact of major geological faults in the stability on backs of open stopes, through the numerical modelling and analysis of overbreak of three case studies. To numerically model the response of the rock mass and underground excavations, a linear-elastic constitutive model using the distinct element method (DEM, software 3DEC1 v5.2) was built. The numerical methodology is divided in three specific stages for each selected case, resulting in nine models in total. Then, based on the results of the numerical modelling, the first and third stage were compared, analyzing if there was an impact caused by the major geological faults in the overbreak on backs of the open stopes. The results show that 𝜎�3≤1𝑀�𝑝�𝑎� remains the criterion that best recreates the overbreak in the cases. Based on the criterion and numerical models, a fault factor for the backs (𝐹�𝑏�) of the open stopes was introduced to improve the empirical stability result of the case studies.