ABSTRACT

Coal production in Ostrava-Karvina coalfield (hereafter OKC) is connected with occurrence of rock bursts. These rock bursts became a serious threat both in view of their consequences and in view of their frequency during seventies and eighties of the preceding century during which the biggest annual coal outputs In history of coalfield were achieved, i.e. 24 million t/a. It was expected, therefore, that the wind-up of coal mining, which occurred during nineties and during which coal production was gradually reduced up to annual output of about 14 million t/a, would be manifested by a reduction of rock burst risk and thus by diminishing of frequency of rock burst events. However, practical results have demonstrated that the risk of rock bursts in OKC is continuously very actual and that the natural and mining technical conditions of coalfield participate in a decisive manner in this problem.

INTRODUCTION

Underground coal mining in OKC has had a more than two hundred years tradition. The biggest annual coal outputs were achieved in 1971 and then during period 1974–1982 and they exceeded 24 million t/a.

Restrictions of coal output connected with closure of ineffective coal mines have started since 1990 In Connection with conversion from central planned economy to market economy. Annual coal output was reduced from 22 million t/a in 1989 to 14 million t/a In 1997 and it has been maintained at such level until nowadays.

Coal mining in OKC has been connected with rock bursts since the beginning of XXieth century (Pelnar 1939). Total number of rock bursts in OKC today is nearing now to 500 cases.

Rock bursts started to be a serious problem during seventies and not only due to their consequences, but also due to their frequency of occurrence. During this period mining penetrated to depth range between minus 600 m and minus 800 m. Coal production was carried out in Lower Such a measures and Saddle seams Were then entered.

It was assumed that the occurrence of rock bursts In OKC is connected both with specific, natural and technical conditions and with high intensity of coal mining within a relatively small area. In view of the last-mentioned circumstance It was expected that a reduction of coal output would have a favourable effect on reducing of risk of rock bursts and thus on diminishing of their number.

However, in spite of this expectation the rock bursts continued to be a serious problem of OKC. And so the decisive factor influencing their development probably are natural conditions given especially by geologic and geomechanical structure of deposit as well as by difficult mining technical conditions which are on the one hand a consequence of mining of multi-seam deposit type in the past and are given on the other hand by selective mining which is applied for economic reasons at present time.

PRINCIPAL CHARACTERISTICS OF OKC AND WIND-UP OF COAL MINING

The Ostrava-Karvina Coalfield is a part of Upper Silesian Hard Coal Basin and it extends on about 20% (approximately 1600 km2)

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