Coal mining in Ostrava-Karvina coalfield is being accompanied by rockbursts. 82 rockbursts occurred within the period between 1990 and 2002. Natural and technological factors from these rockbursts were collected and analysed. They confirmed that rockbursts are complex geomechanical events and that the relations between co-acting technological and natural factors are very complicated.

Der Abbau in dem Ostrava-Karvina Steinkohlenrevier wurde von Anfang an durch Gebirgsschlage begleitet. 82 Gebirgsschlage in dem Zeitabshnitt von 1990 bis 2002 erfolgten. Die Angaben ueber natuerliche und technische Faktoren der Gebirgsschlage wurden gesammelt und analysiert. Es wurde bestatigt, dass die Gebirgsschlage komplexe geomechanische Phanomene sind und dass die Beziehungen zwischen den zusammenwirkenden Faktoren sehr kompliziert sind.

L´abattage d´houille dans le Bassin houiller d´Ostrava-Karvina est accompagnee par les coups de terrains. 82 coups de terrains s´etaient produit dans la periode entre 1990–2002. Les donnees sur les facteurs naturels et techniques ont ete ramassees et analysees. Les resultats ont corrobore que les coups de terrains sont des phenomènes geomechaniques complexes. Les relations entre les facteurs techniques et naturels cooperants sont très compliques.

Introduction

Ostrava-Karvina coalfield (hereafter OKR) in Czech Republic, which is part of Upper Silesian Basin, ranks among the mining coalfields where due to the given natural conditions rockbursts occur. Hard coal seams have been mined in this area by underground mining method for more than 200 years and the first rockbursts were recorded already in 1912. Geological structure is very variable, the deposit has a typical multiseams nature, and vertical distance between seams usually varies from some meters up to several tens of meters.

The rockbursts started to be manifested more frequently during seventies of the past century in Karvina part of the coalfield. Karvina part is featured among other by mean worked thickness of coal seams of about 2.5 m (contrary to nowadays wind-up Ostrava part of the coalfield where mean worked thickness was about 1.1 m). The rock massif in Karvina part, especially in saddle strata, consists mostly of solid siltstones, sandstones and conglomerates with compression strength between 70 and 90 MPa. Compression strength of coal is usually between 20–25 MPa, rarely even 35 MPa. Mining depth is at present about 800 m below surface.

During the last decade of past century an important restriction of coal production occurred in OKR. Reduction of the annual coal production from about 24 mil. t to about 14 mil. t was manifested above all by abandoning of mines in the Ostrava part.

Within the time series of 25 years between 1977 and 2002 it cannot be found out any explicit dependence between volume of coal output (both of total output and of output of rockburst prone seams) and frequency of rockbursts. Thus rockbursts are obviously connected with geological and geomechanical conditions in which mining activity proceeds and equally with intensity and success of continuously performed rockburst control measures.

It results from analysis of nature of rockbursts in OKR that formerly the rockbursts possessed almost exclusively the nature of in-seam rockbursts.

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