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Abstrakt

The coal exploitation in the Upper Silesia region (along the Vistula River) triggers the strata seismic activity, characterized by very high energy, which can create mining damage of the surface objects, without any noticeable damages in the underground mining structures. It is assumed that the appearance of the high energy seismic events is the result of faults’ activation in the vicinity of the mining excavation. This paper presents the analysis of a case study of one coal mine, where during exploitation of the longwall panel no. 729, the high energy seismic events occurred in the faulty neighborhood. The authors had analyzed the cause of the presented seismic events, described the methods of energy decreasing and applied methods of prevention in the selected mining region. The analysis concluded that the cause of the high energy seismic events, during the exploitation of the longwall panel no. 729 was the rapid displacements on the fault surface. The fault’s movements arose in the overburden, about 250 m above the excavated longwall panel, and they were strictly connected to the cracking of the thick sandstone layer.
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Abstrakt

Recalling the body of experience gathered in the collieries of the Upper Silesian Coal Basin, the increased risk of seismicity and rockburst occurrences in confined conditions including the exploitation of remnants were identified. This study investigates geomechanical aspects of longwall mining in the areas affected by old excavations aimed at relaxation of a multi-bed deposits within a thick coal seam or a group of seams. It is assumed that high-energy seismicity is another factor determining the rockburst hazard alongside the state of stress. A case study is recalled, describing a colliery where mining-induced seismic activity of a de-stressed coal seam remained at the level comparable to or higher than it was experienced in the de-stressed seam operations. An analytical model was used to study the stress state and potential loss of structural continuity of an undisturbed rock body surrounding the longwall panel being mined beneath or over the abandoned workings. Recalling the developed model of the system involving nonlinear functions demonstrating the existence of abandoned mine workings within the rock strata, computer simulations were performed to evaluate the rockburst hazards along the face area. Discussions of results are based on observations of immediate roof convergence and the vertical stress concentration factor at the longwall face zone. Computational data of the modelled mining situations demonstrates that despite using the de-stressing method of mining, the occurrence of events impacting on mine working beneath and over abandoned workings cannot be precluded. Here the scale of rockburst hazards is determined by local mining and geological conditions, such as the type and extent of abandoned workings, their age and vertical distance between them and the coal seam currently mined.
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