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Abstract

This article concerns numerical modeling of the impact of mining operations on fault behavior, carried out on the basis of a calculation program based on the finite element method. It was assumed that the fault is a single discontinuity in the form of a vertically-oriented plane, and the conditions in which surfaces merge are defined by the right of the Coulomb friction. On the one hand, the calculations are related to the fault’s response to additional weight resulting from mining operations, and on the other, they are related to the impact that occurrences in the fault’s plane had on the immediate surroundings of the extraction center. The behavior of the fault was analyzed based on distributions in the plane of shear stress and slip, together with their range and energy dissipated due to friction. In turn, the impact of the fault on its immediate environment was analyzed based on variations in the total energy density of elasticity. The results of numerical modeling made it possible to draw conclusions concerning mining operation in the proximity of tectonic dislocations in the context of seismic hazard’s levels.
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Abstract

With reference to the situation experienced in several Polish collieries where the risk of occurrence of gas-geodynamic phenomena is increasing and decisions to start the mining activities need to take numerous constraints associated with previous mining into account, this paper addresses certain geo-mechanical aspects of longwall mining in the zones of excavation edge interactions giving rise to major changes in the conditions of the deposit and rock strata, as a consequence of previous mining operations in adjacent coalbeds. Starting from the analytical description of displacements and stresses in the proximity of longwall mining systems, the paper summarizes the results of model tests and investiga-tions of the influence that the excavation edge has on the behavior and structural continuity of a portion of the coal body in the coalbed beneath or above an old excavation. Based on selected nonlinear functions emulating the presence of edges in the rock strata, a comparative study is carried out by investigating two opposite directions of workface advance, from the gob area towards the coal body and from the coal body towards the gobs. The discussion of the results relies on the analysis of roof deformation and the concentration factor of the vertical stress component at the workface front.
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Abstract

The current rockburst hazard conditions in the copper mines are the consequence of mining-induced seismicity of the rock strata whilst the majority of registered rockbursts have been caused by high-energy seismic events. T he analysis of seismic activity in recent years indicates that the region of the Rudna mine is the region of the highest seismic activity. This paper is an attempt at evaluating the seismicity levels in the Rudna mine in the period from 2006-2015, within the entire mine and in its particular sections. Key parameters of seismic activity include the number of registered seismic events, total energy emission levels, and a unit energy factor. The variability of Gutenberg -Richter (GR) parameters are analyzed and the epicenters’ locations are investigated with respect to the stope position. T he distinction is made between low-energy (103 ≤ As < 105 J) and high-energy (As ≥ 105J) seismic events ahead of the stope, in the opening-up cross-throughs and in the gob areas. It appears that the risk level of a high-energy event occurrence in the R udna mine has not changed in recent years and has remained on a high level whilst the differences in seismic activity, in particular mine sections, are attributed to the varied extraction height and varied thickness of rockburst-prone carbonate layers in the roof of the copper ore deposit. The analysis of the epicenters’ locations with respect to the stope reveals that no matter what the seismic energy levels, the largest number of rockbursts are registered in the opening-up cross-through zone. Low-energy tremors are mostly located in the gob areas, high-energy events occur mostly ahead of the stope. T hus, the evaluation of the seismicity conditions in the Rudna mine seems to positively verify the relationship between the number of registered events and the levels of generated seismic energy, taking the local geological and mining conditions and the specificity of the room and pillar mining method into account.
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