Determining stability conditions for haulage drifts protected by coal pillars

Abstract

The aim of this research is to study the stability of haulage drifts and the manifestations of rock pressure in them lengthwise the working area when protecting them with coal pillars. To assess the stability of workings, field experiments were conducted to study the manifestations of rock pressure in the haulage drifts of a steep coal seam. It has been registered that as the breakage face progresses, the displacement of roof rocks on the contour of the drift linearly increases with an increase in the length of the working area. The deformation properties of coal pillars were studied taking into consideration the extent of the convergence of the roof and soil. This paper reports a theoretical model that describes the destruction of the above-drift coal pillars when unloading the coal-bearing massif that hosts the workings. It has been determined that the equilibrium state of coal pillars is ensured when the specific deformation and stress potentials are equal before the occurrence of main cracks of destruction. As the relative deformation of coal pillars increases at compression, when this equality is broken, the specific energy intensity of destruction increases. It is noted that at a distance exceeding l>10 m behind the breakage face, the occurrence of the main cracks of destruction is followed by a stability loss in the coal pillars. As a result of external forces, the change in the volume and shape of the coal pillars causes the intensification of the process of convergence of lateral rocks on the contour of haulage drifts lengthwise the working area and leads, with a certain degree of probability, to a deterioration in the stability of workings. The results of this study could be used to justify the choice of technique to protect haulage drifts. This would allow the timely development of minefield reserves thereby improving the safety of operations. It is recommended that the technique of protecting haulage drifts by coal pillars should be abandoned