Abstract:The complex hydro-geological situation, particularly in terms of groundwater, has been a constant threat to the mining carried out at the Velenje colliery since its inception. Of particular interest to the authors are the difficulties presented to the colliery by the adjacent sand aquifers, as the water pressure within these sands directly impacts mining safety, and the aquifers themselves are most directly affected by dewatering. In order to monitor water levels and estimate dewatering at the Velenje wells, multi-layered modelling using 3D Finite Difference Method (FDM) has already been carried out. However, FDM is not optimal due to its greater dependence on cell size than on water flow. In 2017 in Velenje, a series of wells will be terminated as a result of mining and mining-induced subsidence, leading to dewatering and danger of flooding. As part of a plan to address this by replacing dewatering structures, a series of drive-in filters will be implemented around the entry and exit point tunnels of a longwall face. Because FDM seems to be inadequate for purposes of optimising this process, the Finite Elements Method (FEM) was applied in this case. Based on such an application of FEM, a prediction of the optimisation of drive-in filters was carried out by the authors.
The Velenje Colliery is operating in the largest coal deposit in Slovenia and at the same time in one of the thickest known coal seams in the world. The lignite seam is at one point up to 165 m thick. Until now more than 220 million tons of lignite coal were extracted from this seam. The colliery is situated in the so-called Velenje depression, which is a component part of the Southern Karawanke geotectonic unit. Considering the coal mining we can claim that rock bursts are a kind of constant that accompany the mining activities and represent occasional difficulties during production and at the same time disturb the local inhabitants. Based on complaints and at the same time because of the need for a thorough understanding of the causes of ground shaking, the Velenje Colliery decided for a systematic monitoring and evaluation of the seismic events. Based on these measurements the seismic events were precisely located and correlated to the technological process itself. Seismic events analysis indicates that these events are instantaneous stress relaxations piled up for a longer time because of the lignite extraction. This last statement can be confirmed by an analysis of the longitudinal seismic waving first arrivals (P) to seismological stations of the state monitoring network of Slovenia, Austria and Italy, even though such events are rare because of their weakness. The same analysis showed that the magnitudes rarely reach over 1.5 of local magnitude after Richter. Simultaneously with the seismic events analysis we analyzed the way of support relaxation. Tests on the existing support type K24 showed that this support is capable of withstanding large stresses without deformation. From these tests we found that the stress relaxation at currently used support type K24 can occur over relatively large deformations. The relatively simple stress-relaxation analysis at existing support shows it surprisingly well match to the energy relaxed at rock bursts in Velenje Colliery. Based on research done between 2003 in 2012 it is possible to conclude that the existing support type must be replaced with one that can relax the stress more frequently and with less deformation, consequently reducing rock bursts and increasing safety at work. Keywords: rock burst, steel arch, induced seismicity Premogovnik Velenje deluje na najve~jem nahajali{~u premoga v Sloveniji, ki je hkrati eno takih, ki ima najbolj debele plasti premoga na svetu. Plast lignita je na enem mestu debela tudi do 165 m. Do sedaj je bilo izkori{~enih 220 milijonov ton lignita iz te plasti. Premogovnik se nahaja v velenjski depresiji, ki je sestavni del geotektonskega dela Ju`nih Karavank. Pri rudarjenju premoga so hribinski udari konstanta, ki spremlja rudarske aktivnosti in ob~asno predstavlja te`ave pri proizvodnji ter isto~asno moti lokalno prebivalstvo. Zaradi prito`b in hkrati zaradi potrebe po razumevanju vzrokov tresenja tal, so se v Rudniku Velenje odlo~ili za sistemati~no registriranje in oceno seizmi~nh pojavov. Na osnovi teh meritev so bili seizmi~ni d...
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