STABILITY ANALYSIS OF THE SUBLEVEL CAVING METHOD

Ground control problems in subievel caving become evident as the rock pressure increases with depth. Recently, a finite element analysis of the stability problems of the sublevel caving method was completed by the authors. This paper summarizes the results of stress analysis in sublevel extraction drifts under different stress field conditions by using linear elastic and nonlinear elasto-plastic finite element modeling techniques. A critical stress concentration will occur in the uppermost sublevel drifts beneath the caved area or blasted ore area. During the blasting and drawing cycle, a tensile and shear failure condition could develop in the central extraction drift when it would be mined last. Under a high horizontal stress field condition, almost all tensile stress in the back of the extraction drifts will be eliminated and only slight yield can be seen in the floor of the extraction drifts. Compared to the cases under the gravitational stress field condition, the total yielding zone will be grtly reduced because of the increase of horizontal confining stress with depth. However, it is predicted that the centre of each ore column side will experience excessive shear stress that probably will result in ore failure.The two major conclusions drawn from this study to improve the overall stability of sublevel caving are: (1) the width of extraction drifts must be carefully controlled and an appropriate stoping sequence selected; and (2) the sublevel caving method can be used in deep mining if the pillar width is increased correspondingly with mining depth.