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تعداد صفحات این فایل: ۲۱ صفحه

بخشی از مقاله انگلیسیعنوان انگلیسی:Impact of longwall mining on groundwater above the longwall panel in shallow coal seams~~en~~

Abstract

Since longwall mining causes subsidence through the overlying strata to the ground surface, the surface water and groundwater above the longwall panels may be affected and drained into the lower levels. Therefore, loss or interruption of streams and overburden aquifers is a common concern in coal industry. This paper analyzed the potential effects of longwall mining on subsurface water system in shallow coal seam. In order to monitor different water level fluctuations throughout the mining period, three water wells were drilled down to the proposed deformation zone above the longwall panel. A GGU-SS-FLOW3D model was used to predict water table contours for the periods of pre- and post-mining conditions. The field data from the three water wells were utilized to calibrate the model. The field test and numerical model can help to better understand the dewatering of shallow aquifers and surface waters related to ground subsidence from longwall mining in shallow coal seam.

۱ Introduction

Longwall mining method is a highly productive underground mining method in which a panel or a block of coal is completely extracted (Peng, 2006, 2008; Qian and Shi, 2003; Wang, 2009). When a longwall panel with sufficient width and length is excavated, the overburden roof strata are disturbed in order of severity from the immediate roof toward the surface, or even the aquifers, which can lead to serious mine-flooding accidents and increasing damages to ecological environments (Miao and Qian, 1995; Qian and Miao, 1995; Qian et al., 1996). Thus it is absolutely essential to determine the degree of dewatering for prevention of water inrush and protection of groundwater resources (Li, 2011; Li and Qiu, 2012). In this paper, three water wells drilled in site and a GGU-SS-FLOW3D model are used to monitor different water level fluctuations throughout the mining period. The potential effects of longwall mining on subsurface water system are analyzed in shallow coal seam with the field data measured from the three water wells and the numerical model.

۲ Geology and mining conditions of study area

The geology of the study area includes sedimentary rocks of Pennsylvanian and Permian ages (Paleozoic). Alluvial deposits of Quaternary age occupy the valley bottom of the dissected topography. The boundary between the Pennsylvanian and Permian systems is indistinct, but it is generally defined by the sequence of rocks extending from the base of the Waynesburg coal bed to the present topographic surface.

The Dunkard Group consists of the Greene Washington and Waynesburg formations. The lower section of the Dunkard Group resembles that of the Monongahela Group which contains laterally persistent Pittsburgh coal. The top bedrock unit is the Dunkard Group, which belongs to the Permian age.

The longwall panels B5 and B6 studied in this paper are located in the Appalachia Coalfield, United States (Fig. 1). The overburden depth varied from 600 ft to 900 ft (1 ft ¼ ۰۳۰۴۸ m). The average mining height was 7 ft. The length of panels B5 and B6 was 12,000 ft and 5700 ft, respectively. The width of the both panels was 1433 ft. The width of headgate and tailgate entries was 16 ft. The chain pillar system between panels B5 and B6 was 200 ft wide. The average longwall face retreat rate was 30e50 ft/d during the longwall face mining in the study area.

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