Henryk Kleta

The assessment involving the prospects of mining exploitation, in particular with the disruption of protective pillars, is frequently a fundamental issue in the engineering practice. It is even more important when the problem involves the completed mining exploitation which was carried out for many years and which already brought about stress-strain changes in the protected objects whose technical condition should ensure safety of use.
The impact of mining exploitation on rock mass and surface ground can be most reliably determined basing on the results of geodetic surveys, but in practice, in the conditions where mining exploitation was carried out for many years, the results of geodetic surveys with the records of deformations that occurred in such areas are not available. Then, to assess the impact of mining operations carried out so far, we can only apply the available partial results of geodetic surveys. It happens in situations when we are to assess the prospects of mining exploitation, especially with the disruption of the protective pillar of mining shafts, which are of fundamental importance for mining operations.
The article presents an exemplary assessment involving the prospects of mining exploitation with roof fall in the protective pillar of shafts in terms of the results of the reprognosis involving the impact of completed mining exploitation on the surface ground and rock mass.
The methodology used to assess the prospects of further mining exploitation in the vicinity of the protective pillar of main shafts takes into account the fact that in view of the reprognosis results, years-long mining exploitation carried out to the boundaries of the protective pillar resulted in relatively large horizontal displacements around the area of the shafts, and smaller vertical displacements. In such circumstances, the latest surveys of horizontal displacements were used to infer about the current curvature of the vertical axis of shaft No.1, located closest to the plots of the completed mining. The calculation involving the possibility to carry out further mining operations within the impact range on the protected shafts No.1 and No.2 was determined by comparing the calculated permissible curvature radius of the shaft axis, reflecting the strain efficiency of the lining, with the calculated curvature radius of the vertical axis of the shaft lining effected by horizontal displacements of rock mass.