Materiały konferencyjne SEP 1992

456 Underground Exploitation School '92 1. Introduction Coal mining in the German Ruhr-district wi 11 gain greater depth in futurę, and therefore the młnes have deal with increas- ing stresses. Faster advances of the working-faces will induce additional forces too. Thus the danger of coal outbursts will remain and probably increase in futurę with coal mining in the Ruhr area. Of course not every mining area is outburst-prone. Special conditions are reąuired to msike an area dsingerous with respect to outbursts. Since now there is no complete physical theory de- ser i bing outbursts and the conditions producing such events. Therefore empirical data have issued special regulat ions. They define the condit ions under which an area is considered out- burst-prone. In the first chapter of this paper regulations are summarized. In areas which are considered as outburst-prone due to the regulations the mines are reąuired to carry out test drillings. If some of these test dri 1lings show "critical results"» the area of t hese dr i 11 i ngs i s des i gnat ed an "area of recogni zed outburst-danger", and destressing operations have to be carried out. With few exceptions, where destressing blastings are applied, destressing drillings are used. The decision whether a test drilling has a "critical result" or not depends on the measured volume of coal drilled out per meter and on subjectively observed so-called seam-reactions. The method of test-dri11ing together with destressing techniąues is described in the second chapter of this paper. As the distinction between critical and uncritical test- dri 11 ings also follows empirically found thresholds, different attempts have been made to improve the process. One approach is to devełop eąuipment and evaluating-methods for objectiye measu- rements of seam-reactions. Some results of this are described in the third chapter. In addition to dri11-cuttings and seam- reactions also technical drilling parameters, such as rotational speed, torąue and axlal force, might give valuab1e informat ions about the dri11ings. Therefore basie invest igations have been carried out, and some results of these are shown in chapter