Deformation and seepage characteristics of gas-containing coal under true triaxial stress
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ORIGINAL PAPER
Deformation and seepage characteristics of gas-containing coal under true triaxial stress Wenzhou Du 1,2 & Yansong Zhang 1,2 & Xiangbao Meng 1,2 & Xinyan Zhang 1,2 & Wenxin Li 1,2 Received: 16 November 2017 / Accepted: 16 April 2018 # Saudi Society for Geosciences 2018
Abstract Conventional triaxial tests were mostly conducted to explore the coal and gas outburst mechanisms based on the moulded coal specimens, leading to the difference of three-dimensional unequal stress condition between the simulated coal seam and the real coal seams. A true triaxial gas-solid coupled coal seepage test system was developed to fulfil the gas seepage under the true triaxial stress. Moreover, the deformation-failure characteristics and gas seepage behaviours of moulded coal and raw coal were investigated under true triaxial stress. By analysing the relations among stress, strain and permeability in true triaxial tests, it has established the important effect of the intermediate principle stress (σ2) on the occurrence of coal and gas outburst. The coal’s yield strength increased and permeability decreased when σ2 was at the early and middle stage of the load, while the coal’s permeability increased and instable failure happened when σ2 was at the late stage of the load. Particle flow code software was applied innovatively to simulate the seepage experiment, proving the reliability of experimental results. Meanwhile, the test standard based on raw coal was proposed. Furthermore, the present research results provide a new insight and approach for the prevention and monitoring of coal and gas outburst. Keywords True triaxial . Coal and gas outburst . Mechanical properties . Seepage of gas . Intermediate main stress . PFC
Introduction Coal and gas outburst is a serious threat on coal mine safety. Up to now, it has occurred in at least 16 countries with grave causalities and huge economic losses. Half of these accidents occurred in China (Hu and Wen 2013; Lama and Saghafi 2002). When coal and gas outburst occurs, a great amount of coal and gas is spontaneously ejected to the roadway or the stope in a short time (Hu and Wen 2013). It could be triggered by many factors including crustal stress, gas, coal properties, geological conditions and human factors (Beamish and Crosdale 1998; Noack 1998; Shepherd et al. 1981; Ulery 2006; Wold and Choi 2001). Although the mechanism is still not fully
* Yansong Zhang [email protected] 1
College of Mining and Safety Engineering, Shandong University of Science and Technology, Room 203, 579 Qianwangang Rd, Huangdao District, Qingdao 266590, People’s Republic of China
2
Mine Disaster Prevention and Control-Ministry of State Key Laboratory Breeding Base, Shandong University of Science and Technology, Qingdao 266590, People’s Republic of China
understood, crustal stress and gas are considered the major causes, and a great deal of research on coal’s deformation and failure and the gas’s seepage characteristic in the coal has been done, for which the physical test is the most direct and e
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