Determination of actual limit angles to the surface and their comparison with the empirical values in the Upper Silesian Basin (Czech Republic) Marian Marschalko a ,Işık Yilmaz b, ⁎, Veronika Křístková a , Matěj Fuka a , Martin Bednarik c , Karel Kubečka d a VŠB-Technical University of Ostrava, Faculty of Mining and Geology, Institute of Geological Engineering, 17 listopadu 15, 708 33, Ostrava, Czech Republic b Cumhuriyet University, Faculty of Engineering, Department of Geological Engineering, Sivas, Turkey c Comenius University, Faculty of Natural Sciences, Department of Engineering Geology, Mlynská dolina, 842 15, Bratislava, Slovak Republic d VŠB-Technical University of Ostrava, Faculty of Civil Engineering, Department of Building Structures, 17 listopadu 15, 708 33, Ostrava, Czech Republic abstract article info Article history: Received 17 May 2011 Received in revised form 30 September 2011 Accepted 13 October 2011 Available online 21 October 2011 Keywords: Limit angle Undermined territory Black coal deep mining Czech part of the Upper Silesian Basin This study deals with the determination of the actual limit angles in the long-term formed subsidence basin in the Czech part of the Upper Silesian Basin (the remaining part lays in Poland). Here there was the most extensive underground exploitation of black coal in the north-east of the Czech Republic. A limit angle is ab- solutely decisive in the determination of deep mining influences in relation to the current and future utilisa- tion of this territory. The two CSM and Paskov mine localities on the edge of the subsidence basin were selected for this study, since they could not have been affected by mining in neighbouring mines. On the grounds of the long-term levelling monitoring of points on the surface which started prior to mining, the hor- izontal distance between the mined out area and the undisturbed ground surface was identified. The impact of limit angle on the surface was calculated by means of the horizontal distance and the established mining depth. Such identified actual limit angles reached the values of 36° at the CSM Mine and 25° for the Paskov Mine. The calculated values are significantly lower when compared with the currently applied empirical values of 57° for the CSM Mine and 56° for the Paskov Mine. This means that the extent of the undermining effects is unambiguously wider by 611 m at the CSM Mine and by 883 m at the Paskov Mine. This study thus establishes the existence of a significantly vaster area influenced by coal deep mining than previously expected. The identified facts lead to the conclusion that regular revisions and follow-up updates of the em- pirically determined parameters are recommended. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Conflicts of interest play an important role during black coal deep mining in relatively densely populated territories. Under the rule of law in the majority of countries, organisations implementing black coal deep mining are obligated to inform all the land owners about their working plans. Prior to extraction, the organisation must deal with all conflicts of interest of every land owner in the relevant territory. Therefore, calculation of the expected effects of mining and the ex- tent and intensity of undermining are substantial factors. The key pa- rameter to determine the extent of a subsidence basin, i.e. the extent of a territory influenced by the effects of deep mining, is the so- called limit angle (Aksoy et al., 2004). Empirical values of limit angles have been determined and generally accepted during approximately a hundred years experience of coal deep mining in the north-east of the Czech Republic and southern Poland (Neset, 1984). These values were determined for specific deep mining regions in different coun- tries predominantly dependent on the geological structure of the lo- cality (Singh and Singh, 1998)(Table 1). Currently, values of the empirical limit angle are used to predict the effects of undermining. Within this prediction, empirically determined values of the limit angle are merely adjusted to the depth of coalfaces whose exploitation is expected in the near future. Such adjusted, but still empirical values, form the basis for a two-dimensional model of a subsidence basin, which results in the determination of expected influ- ences on the ground surface above the planned coalfaces (Alejano et al., 1999; Torano et al., 2000; Cui et al., 2001). Based on the long-term levelling measurements of points on the edge of a subsidence basin, the presented study identifies the actual limit angles in two geologically different localities. The most impor- tant aspect of the study is that a locality was found which is actually situated on the border of a subsidence basin. The choice of this local- ity was not easy since the allotments in this study area border one another and their subsidence basins often interfere with one another. Geographically, both localities are situated in the north-east of the Czech Republic, and geologically this is in the Czech portion of the Upper Silesian Basin. The first studied locality is part of the CSM Mine Engineering Geology 124 (2012) 130–138 ⁎ Corresponding author at: Cumhuriyet University, Faculty of Engineering, Department of Geological Engineering, 58140 Sivas, Turkey. Tel.: +90 346 2261527; fax: +90 346 2191171. E-mail addresses: iyilmaz@cumhuriyet.edu.tr, isik.yilmaz@gmail.com (I. Yilmaz). 0013-7952/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.enggeo.2011.10.010 Contents lists available at SciVerse ScienceDirect Engineering Geology journal homepage: www.elsevier.com/locate/enggeo