This research evaluates two methods for determining the optimal dimensions of a fictive room and pillar (R&P) mine at the Marche Les Dames (MLD) quarry in Belgium. The empirical method, including the Q-system and the R&P design guidelines from NIOSH (2011), is used to calculate roof spans and pillar dimensions. These calculated pillar dimensions are then modelled using the Distinct Element Method (DEM) software, 3DEC, and the results will be compared with those of the empirical method. The pillar is modelled using a Bounded Block Model (BBM) approach and integrating a Discrete Fracture Network (DFN) to account for the fractured rock mass. The empirical method offered straightforward results and is well-suited for preliminary mine design. However, it is unable to incorporate the heterogeneity of the rock mass, providing only a limited understanding of its behaviour. In contrast, the numerical method can incorporate this heterogeneity, offering a more detailed analysis. However, collecting all necessary parameters is challenging, and calibration and validation are required—something that was not fully achieved in this research.

The study found that the numerical model produced unrealistic results when modelling stresscontrolled failure in the pillars at MLD. The pillar strength was much higher than expected. This was attributed to the calibration of the intact rock strength using a UCS sample, which did not account for weaknesses in the intact rock. In contrast, when the failure was structurally controlled and the model did not require the BBM approach, the results were much more realistic, with significantly lower computational time. Still, it is recommended to use the numerical model primarily to investigate the impact of specific features such as karst voids and dissolution joints, which the empirical method cannot incorporate, rather than to determine overall mining dimensions.