The contribution informs about practical application of a system of detecting and predicting of unfavourable stress conditions in rock massif with rockburst risk in Ostrava-Karvina coalfield. The geological and mining characteristics of the south part of carboniferous hard coal deposit, straddling on the border between Czech Republic and Poland are briefly described. Further the problems of stress measures and practical use of stress determination and rockbursts prediction in conditions of sedimentary coal deposit is discussed. In the end the results and successfulness of the rockbursts prediction in Ostrava-Karvina coalfield are presented.
Ostrava-Karvina coalfield (hereafter OKR) is the Czech part of Upper Silesian hard coal basin (see Figure1). Due to geological characteristics of rock massif and due to long-term mining activity stress Concentrations occur in some parts of the rock massif while in other parts the rock stress is relieved. Irregular distribution of stress and of its concentration in certain parts of rock massif can lead when exceeding rock strength limit to a sudden release of elastic deformation energy and to a occurrence of rockburst. A considerable attention to this problem has been dedicated in OKR for almost hundred years, as the first reports of underground rockbursts are dated in our region already in the very beginning of past century. Prediction of increased stress zones and thus of potential rockburst risk zones ranks among the most difficult tasks of rockburst control. However, because it is desirable to recognize such danger as accurately
(Figure in full paper)
as possible, a system of rock burst prediction has been developed in OKR. The aim of the following paper is to make acquaintance with this prediction system.
In OKR a multiseam sedimentary hard coal deposit is exploited. An area of about 1550 km2 is covered by Carboniferous measures that reach in the part being exploited a total thickness of up to 2000 m. The geological structure is a result of several geological genesis cycles. It is essentially changing in west-east direction. Based on geological differentiation the Ostrava-Karvina coalfield has been structured into a western part (Ostrava part of basin) and into an eastern part (Karvina part of basin). It is proper to mention here that at present time only the eastern Karvina part of OKR is being exploited, while the mining in the western Ostrava part of OKR has been stopped.
In the western part of OKR the measures of a paralic sedimentary development are deposited. They are featured by shorter sedimentary cycles and thus by a thinner thickness of rock strata including coal seams. In general there are less sandy rocks. The mudstones and siltstones which have a lower compression strength than that of sandy rocks occur in the lithological sequence more frequently than in eastern part of OKR. In the eastern part of OKR the paralic series were covered by sedimentation of continental molasse measures. In contrast to lithological nature of western part of OKR the sedimentary cycles are conspicuously longer and moreover sandy rocks are prevailing.