The dimensioning of pillars in the mining rooms and pillars method through a detailed evaluation of the stress conditions in the rock

摘要

The determination of the minimum side length of rock pillars in the room and pillar method is of fundamental importance in mining engineering. In the last decades some simple analytical equations were used for this aim: the area of influence method and different empirical formulations for obtaining the pillar strength. This kind of approach can lead to overdimensioning or critical stability conditions, with the risk of the miners being involved, should the pillars and the room collapse. In order to conduct a detailed analysis of the stress conditions inside pillars, a parametric analysis with tri-dimensional numerical modelling was carried out. This made it possible to identify a critical point, where the minimum local safety factor is 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, obtained in function of the width/height ratio of the pillar, it was possible to evaluate the local safety factor in the aforementioned critical point, the geometric and geomechanical parameters of influence being known. The dimensioning of the pillars through the local safety factor at the critical point makes it possible to avoid overdimensioning and static problems, which instead can occur when simplified calculation methods are used.