Rock pillars can be defined as the in-situ rock between two or more underground openings. However, one aspect that is seldom considered in analysis of hard rock pillars, and indirectly in synthetic rock mass models to determine rock mass strength, is the actual stress level and stress path imposed on the pillar due to the excavation sequence and the location of the pillars within the mine lay out. In this paper we propose to use numerical stress analysis to determine how stresses vary across the excavated pillars in a typical room-and-pillar mine lay out, and thus generate a spatially variable determination of pillar stability. Because of the computational difficulty associated with hybrid modelling of realistic discrete fracture networks, synthetic rock mass modelling is commonly carried out using a 2D approach. By comparing 3D and 2D results for selected cross-sections across, we believe the results of the analysis will provide the opportunity to better constrain the stability implications of a 2D approach to pillar design and synthetic rock mass modelling.
Rock pillars can be defined as the in-situ rock between two or more underground openings. Over the past decades hard rock pillars have been the subject of many studies that have culminated in the formulation of empirical pillar strength equations [e.g., 1 to 7]. In the past 20 years we have also observed the focus of the research shifting from empirical observations to numerical analysis [e.g., 8; 9, 10, 11, 12]. Numerical models allow to include scenarios that transcend those encountered in a mine, and to study the failure process in more details. However, despite increased modelling ability, full-scale forward modelling of mine systems remains problematic. Numerical models either trade the lack of explicitly considering fracturing and kinematics processes for a 3D mine system and the assumption of the rock mass being an equivalent continuum media, or they do consider explicit simulations of fracturing and kinematics processes but limited to 2D/3D analysis of limited system, as in the cause of numerical simulations of pillar strength.
To this date the introduction of a 3D mine system model being able to incorporate fracture mechanics principles at the level required to capture failure both globally and locally, while at the same time including a detailed representation of the rock mass structural character, remains a challenge. Modelling thus requires the real problem be idealised and simplified. In this paper we attempt to define the impact that such a simplification may have on design consideration, by including a comparison between 2D and 3D modelling approaches, and single system analysis (isolated pillar) versus mine systems (mine layout).