Rock pillar stress analysis to obtain effective dimensioning and guarantee the mining void stability

In the room and pillar mining method, dimensioning of the pillars is of fundamental importance. Nowadays, the area of influence method is typically used for dimensioning of the pillars; however, over-dimensioning or critical stability conditions can happen in this method. A parametric analysis with three-dimensional numerical modelling was carried out to study the stress conditions of rock pillars in details. This helped to identify a critical point, where the minimum local safety factor was reached, at the corners of the pillar close to the roof of the mining room. Through the estimation of the major principal stress at the critical point, it was possible to evaluate the minimum local safety factor through the geometric and geomechanical parameters of the problem. The dimensioning of the pillars through the local safety factor at the critical point helps to avoid over-dimensioning and static problems, which can occur when simplified calculation methods are used. The use of the proposed figures can allow a fast pre-dimensioning of the pillars, leaving the more detailed numerical modelling only for the found geometric configuration.