Systematic Mining of the Shaft Safety-pillar

Abstract

The proper functioning of the shaft must be safeguarded for dozens of years until the closing down of the pit. If mining of the shaft pillar is planned at any time during this period, measures of shaft support and general mine engineering must be undertaken to avoid damage to the shaft and consequent dislocation of production. The section of the shaft passing through water-bearing surface rock is in particular need of protection. In this area in recent shafts, the transmission of friction forces from strata to inner shaft structure is inhibited by a bitumen filled slip joint inserted between the outer layer of concrete and the actual shaft lining (Fig. 86). If all strata movement is to be kept well away from the shaft, then working can only be permitted outside the limit-angle cone (Fig. 77). An extraction-free zone marked out on the basis of the angle of break is insufficient for this purpose, as the upper shaft structure will still be affected by movement ahead of the face when working from the edge of the shaft pillar.