1、英文原文Aquifer protection during longwall mining of shallow coal seams: A case study in Shen dong Coalfield of ChinaDong-sheng Zhang, Gang-wei Fan,Li-qiang Ma,Xu-feng WangSchool of Mines, China University of Mining and Technology ,Xuzhou 22116,PR ChinaState Key Laboratory of Coal Resource and Safe Mini
2、ng, Xuzhou 221008,PR ChinaAbstract: Large-scale underground mining of shallow coal seams can have significant impacts on ground surface and potentially leads to incidental damage to the overlying aquifer with subsequent environmental hazards. In order to deal with the apparent conflict between water
3、 protection and high production in underground mining, an aquifer protection mining technique was trialed in panel#51201 in the Shang wan colliery, the Shen dong Coalfield, China. Overburden failure ,water level of the unconsolidated aquifer, surface cracks, and ground subsidence were monitored in a
4、 series of boreholes using bores cope, and also by observations in a nearby water well and by surface surveys. Monitoring results indicate that the aquifer protection mining technique can be successfully applied by modifying a few mining parameters such as mining height or advance rate under some su
5、itable geological conditions. The critical zone in the stratigraphy appears to be the weathered bedrock located immediately below the aquifer. The weathered bedrock will remain impermeable after mining as long as its thickness is greater than the mining height. The development of the mining-induced
6、overburden failure is affected by the key strata but ultimately controlled by the soft aquiclude such as the weathered zone. It was observed respectively that the height of the caved zone was observed to be 5 to 6 times the mining height, whilst the height of the fractured zone is about 10 to 11 tim
7、es the mining height.1 IntroductionThe Shen dong Coalfield, located in the east of the Mu Us Desert, is one of the most representative coalfields in the northwest of China. The coal seams are of the Jurassic period and are typically covered by a thin layer of bedrock. The topmost stratum is alluvial
8、 sand which hosts the only available groundwater resource at its base. Large-scale longwall mining of shallow coal seams can disturb or even damage the overlying aquifers(Li and Zhou,2006;Zhang and Shen,2004),and thus can lead to considerable water loss and aggravation of the vulnerable ecological e
9、nvironment. The protection of water resources associated with the large-scale and high-efficiency mining of shallow coal seams has been a challenge in terms of coal exploitation in the northwest of China (Zhang et al.,2009a,b).Some academic studies have been conducted and operational experiences hav
10、e been obtained since the conceptualization of water protection mining(Liu et al.,2006;Shi et al.,2006).However, all the practices were based on shortwall mining scenarios where reasonably sized pillars are left to protect the aquifer from mining-induced damage. Aquifer protection mining techniques
11、should be considered to be applied in western coalfields of China in order to maximize the economic benefits and coal recoveries with due safety and environmental considerations. This will enable the mining-induced dropdown of the groundwater to be restored to its original level. Practical experienc
12、es have proven that under suitable geological conditions the water level can recover after longwall mining within a certain time period, although the aquifer may have been disturbed by longwall mining(Booth and Bertsch,1999;Booth and Spande,1992;Booth et al.,2000).The key strata theory(Qian et al.,2
13、003),a new approach in the study of aquifer protection mining, provides a better understanding of the governing laws of the overburden crack propagation and distribution caused by the longwall mining. The theory states that (1)the strata that control the entire or partial overburden movement are cal
14、led key strata. It is defined as the main key-stratum if it controls the entire movement, or as the sub key-stratum if it partially controls the movement;(2)the key strata are always the strongest and thickest rock strata, but not all the thick strata are key strata. Apparently, there may be more th
15、an one sub key strata, but there can only be one main key-stratum; and(3)the movement of key strata controls the temporal and spatial distribution of the bed separations, which are always beneath the key strata.Zhang et al.(2009a,b)described the aquifer protection mining technologies and applicable
16、conditions based on the characteristics of the Shen dong Coalfield. The necessary geological factors for aquifer protection mining include the presence of a severely weathered bedrock formation, the number of key strata, and their locations. The available technologies consist of lowering mining height and the use of backfill or slurry injection in some localized region. Zhang et al. (2009a)presented a detailed classification system for the conditions applicable to aquif
