Abstract
In Poland, for underground hard coal seam extraction, the longwall method is used. Retreat longwalls with natural roof caving in the gob are the most common. Currently it is estimated that about a half of the hard coal output in Poland originates from seams located in areas of rock burst hazard. The article shows information about 18 rock bursts, and 14 other seismic events which occurred between 2003 and 2012 in underground mines belonging to one of coal companies in Poland. In addition, negative consequences of those dynamic phenomena in the longwall workings are described. In the next part of paper, the most common types of damage to powered supports after the rock mass tremors and other dynamic phenomena in longwall workings are shown. In order to avoid damage of powered supports, in geo-mining conditions where dynamic phenomena occur, different types of protective means are applied. In the paper the methodology of assessing the powered support yield ability is described. At the end, an example of the assessed yield ability of a powered support in given geo-mining conditions of a longwall face affected by the seismic events is presented.
Highlights
In Poland production of hard coal is conducted in increasingly harder geological and mining conditions, resulting from, among others, still growing depth of mining operations and numerous former exploitation in the mined longwall panels in form of edges and/or residues
Rock mass tremors induced by mining operations may result in rock bursts or decompressions
The presented method, formulated at GIG is commonly used in practice to assess or improve flexibility of powered roof support sections which are to work in Polish hard coal mines, in areas where rock mass tremors occur
Summary
In Poland production of hard coal is conducted in increasingly harder geological and mining conditions, resulting from, among others, still growing depth of mining operations and numerous former exploitation in the mined longwall panels in form of edges and/or residues. According to Polish regulations a rock burst is defined as a dynamic phenomenon caused by a rock mass tremor which results in destroying or damaging a working, or its fragment, leading to the complete or partial loss of its functionality or. While decompression is defined as a dynamic phenomenon caused by a rock mass tremor which causes damage to a mine working (or its fragment), yet does not result in loss of functionality nor renders it unsafe for personnel. In areas where dynamic phenomena occur, requires considering both static and dynamic load while designing support both for headings and longwalls, as, when a tremor occurs, there is an increase in the value of load exerted on a support, and the main task of a properly designed support ought to be maintaining stability of a mine working and providing proper level of safety for the personnel
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