1、英文原文Stress evolution with time and space during mining of a coal seamWei Yanga,b, Bai-quan Lina,b, Yong-an Quc, Zi-wen Lia,b, Cheng Zhaia,b, Li-li Jiad, Wu-qiang Zhaoca Faculty of Safety Engineering, China University of Mining & Technology, Xuzhou, Jiangsu 221116, Chinab The State Key Laboratory of
2、Coal Resources and Mine safety, China University of Mining & Technology Xuzhou, Jiangsu 221116, Chinac Hancheng Mining Co. Ltd., Shanxi coal, Hancheng, Shanxi 715400, Chinad College of Literature, Law & Politics, China University of Mining & Technology, Xuzhou, Jiangsu 221116, ChinaAbstractMining of
3、 the upper protective coal seam is widely practiced in China for coal mine safety, but relief gas may present a new risk of blasting. To control the relief gas effectively, a strain-soften model was built by FLAC3D software to investigate the stress evolution during the process of mining the upper p
4、rotective coal seam. The results show that the abutment stress changes rapidly within 10 m in front of the coal face, and the maximum abutment stress is approximately twice the original when the coal seam is mined 2030 m. The abutment stress should break the rock mass and cause the gas to flow easil
5、y. In the stable mining period, the change trends of the x -stress and z -stress are different, and these should also pre-break the rock mass. The stress distributions of the rock mass at different distances under the protective coal seam are different, especially near the coal face, which should gr
6、eatly affect the gas flow when the space of the protective and protected coal seams change over a large range. The relief angle also changes over a large range, increasing to a maximum approximately 30 m behind the coal face, and it decreases gradually when it is far away from the protective coal se
7、am. The results are helpful for designing the coal face of protected coal seams and borehole layouts to control the relief gas.1. IntroductionChina is a country rich in coal resources but poor in oil and gas. For many years, coal has supplied more than 70% of Chinas energy. In 2010, coal production
8、reached approximately 3.2 billion tons, and it currently supports the rapid growth of Chinas GDP. However, more than 95% of Chinas coal mines are underground, and 17.6% of key state-owned coal mines are coal and gas outburst mines, which seriously threaten coal mine safety. In 2008, for example, 25
9、accidents caused 120 deaths. To effectively control coal and gas outburst accidents, the State Administration of Work Safety unveiled the Provisions for the prevention of coal and gas outburst in August 2009, which stresses regional gas control mainly by mining protective coal seams and by methane p
10、re-drainage to eliminate the risk of outburst from a large region. Additionally, the mining of protective coal seams should be preferentially selected if possible 1.After the protective coal seam is mined, the stress of the protected coal seam decreases and the permeability increases, which causes t
11、he methane to be released continuously, and the outburst danger is eliminated 2 , 3. However, during the process of mining the protective coal seam, the relieved gas from the current and adjacent seams may flow into the coal face, causing the methane to overrun. The relieved gas flow and the protect
12、ed range are determined by the stress distribution 4. The stress distribution of mining fields and roadways has been extensively studied for many years, but most of these studies only address some static states 5 ,6. Because mining is a dynamic process, the stress field evolves dynamically with time
13、 and space, which causes the gas flow and the protected range to change dynami-cally 7. Therefore, the stress distribution during the process of mining a protective coal seam must be studied from a dynamic viewpoint while considering the stress evolution with time and space for gas relief control an
14、d coal face arrangement. However, this question is not addressed in the current literature, so it is necessary to study the issue thoroughly.The geological condition of a coal mine is non-uniform and complex, which makes it a challenge to study the stress distribu-tion and evolution with time and sp
15、ace with only field or laboratory experiments. Professional geotechnical numerical ana-lysis software could be a good choice for this situation.2. Establishment of a numerical modelFLAC3D is one of the most important numerical software tools in current rock mechanics calculations. This tool is parti
16、cularly suitable for solving nonlinear large deformation problems in geotechnical mechanical engineering and is widely used in the field of mining engineering, among other fields 8 ,9. The software contains eleven kinds of material constitutive models, as follows: one empty element model, three elastic material models and seven plastic models. Mining a coal seam will cause rock mass deformation and will decrease the rock strength; thus,
