PARTIAL MINING IN THE SAFETY PILLARS FOR THE SHAFTS OF THE MINE "JAS-MOS"

The mining of stone coal strata causes tension and deformation stresses in the massif of orogen and in this connection some deformations of the area and of the shaft tube, too. To protect theses objects from being damaged safety pillars are set up. A safety pillar is a part of orogen under a protected object in the shape of a truncated cone (and with an angle of Psi dependent on the category of resistance of the object) which is mined on a limited scale. The pillar contains some coal resources which are difficult to excavate. The term of safety pillar was established decades ago and it fulfilled its role in the so called "shallow mining". In the case of deep mining of today already considerable resources are contained in the safety pillar which are very valuable because of their near situation and very high geological knowledge. The authors of the paper present on the grounds of observations and geodetic measurements carried out in three mines working coal strata at the depth below 400 m, in which, in different degree, the bounds of safety pillars of the pit shafts have been disturbed and on the grounds of numeric calculation verifying the measurements a new shape of safety pillar for the pit shaft (having a bulgy shape and not that of a truncated cone) making it possible to win back a part of resources disturbing the stability of pit shaft tube. This doesn't require additional investment costs and assures an unmenaced functioning of the pit shaft. New computer techniques and their turbulent development in the recent years have made it possible to build a theoretical model of the orogen possessing variable geo-mechanical parameters and a high degree of complication. Numerical calculations carried out on its basis make it possible to "observe" any phenomena occurring in the orogen, their interpretation and comparison with geodetic measurements in a reality-near way. The paper presents the process of modelling a lot of variants of the orogen being different in their properties and containing mining excavations; a pit shaft and an output wall in many configurations It also presents maps of distribution of partial stresses in the whole volume of modelled orogen formed on the grounds of numeric calculations. A graphic visualization of modelled orogens and maps of distribution of partial stresses during the presentation of the paper increase the attractiveness of the topic, which enables the audience to understand, in an easy way, the geo-mechanical phenomena occurring in the orogen close to protected pit shaft. Making use of the above conditions in he Stone Coal Mine "JAS-MOS" in Jastrzebie Zdroj a way of mining the region of safety pillar "JAS-V" was designed, which allows, thanks to elongation of he course of the walls, to additionally win about 775 thousand tons, which makes 3,5 output of the mine a month.