Materiały konferencyjne SEP 1992

430 Underground Exploitation School '92 tegic principles cannot be applied. For example» there is no protect ive seam deve1oped, the variat ions of seam thickness are such that the seam cannot be aimed out completely, tecto- nic faults are such that the necessary geometry of the face or its minimum dimensions cannot be ensured, etc. - There are other dangers which must be respected, such as leakage of mine air between adjacent mines, spontaneous igni- tion of coal, subsidence, etc. Thus, there is no generał rule that strategie principles of rock burst prevention must be observed in ałl circumstances. The most adeąuate procedures should be determined In accordance with the situatŁon of the site. The other actłve measures should be always applied in mine workings classified in the third degree of danger even if the resuits of prediction are favourable. In case of unfavorauble resu 11s more measures have to be appl ied. In the mine workings classified in the first or the second degree of danger the acti- ve measures are applied upon the resuits of prediction. Drllling of distressing boreholes is a very efficient method of prevention. Provided that the necessary technological means are avai labie, it can be used in most of the situat ions encountered in mines. The importajit thing for ensuring its effectivity is to determine adeąuate diameter, depth, spacing and distributlon of boreholes. The diameters of distressing boreholes used in OKD are 115 and 200 mm. The dłstance between the boreholes in 2 to 5 m. To illustrate the distressing effect it may be mentioned that in some cases the volume of chippings measured from dri 11 ing one meter of such a borehole is up to several cubic meters in spite of that the volume of a cylinder of one meter length and 200 mm diameter is only 314 cubic centimeters. Distressing blasting works in coal occupy an important place in the prevention. It is a very operative method. In OKD. The Bureau of Młnes approved the increase of charge per hole up to 10 m length for distressing blasting. At the time. other measures prescrlbes for gassy mines were made more severe. Water infusion into coal seams is one of the oldest methods of rock prevent i on. Water i nfused trough boreho1es penetrat es