Experimental study on dynamic mechanical responses of coal specimens under the combined dynamic-static loading
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ORIGINAL PAPER
Experimental study on dynamic mechanical responses of coal specimens under the combined dynamic-static loading Pengfei Lyu 1,2 & Xuehua Chen 2 & Guangbo Chen 1 & Lin Qiu 1 Received: 24 October 2019 / Accepted: 3 September 2020 # Saudi Society for Geosciences 2020
Abstract Dynamic mechanical responses of the coal and rock mass under the combined dynamic-static loading are critical issues for exploring the disaster-causing mechanism of rock burst in coal mining. In this paper, the acoustic emission (AE) technique and high-speed camera imaging were employed, and the burst proneness of the coal specimen, the variation of AE parameters, the specimen failure mode, and the particle distribution of the fractured specimens were investigated by the combined dynamic-static loading experiments. The results indicate that the burst proneness of the coal specimen increases non-linearly as the dynamic loading rate increases. Both the energy input rate, the ringdown counts, and the hits undergo the slow increase, fast increase, and abrupt increase stages. The failure mode of the specimen is changed from shear failure to axial splitting and the final bursting failure. The relationships between the fractal dimension of the specimen fragmentation mass and the dynamic loading rate can be described by a quadratic function. When the specimen reaches the maximum damage degree, an extreme value of the dynamic loading rate (2.8 × 10−3 s−1) is obtained in experiments. The disaster-causing mechanism of rock burst induced by the combined dynamic-static load is discussed from the aspects of the burst proneness of coal specimens, dynamic variation of AE parameters, the change of failure modes of specimens, and the propagation and coalescence of microcracks. Keywords Combined dynamic-static loading . Dynamic mechanical responses . Coal specimens . Rock burst
Abbreviations AE Acoustic emission MTS Material testing system SHPB Split Hopkinson Pressure Bar List of symbols Q Amount of energy input of coal specimen, J σ Stress of coal specimen, MPa ε Strain of coal specimen V Volume of coal specimen, m3 E Energy release of vibration event, J N The vibration frequency that is no less than lgE a A constant positively related to the vibration intensity
b
M Mmax U U0 d
A constant negatively related to the ratio between the high-energy earthquake events and the low-energy earthquake events The mass of the specimen fragmentation, g The maximum mass of the specimen fragmentation, g The number of fragmentations with a mass no less than M The number of fragmentations with the maximum mass The fractal dimension of the fragmentation mass
Introduction
Responsible Editor: Murat Karakus * Pengfei Lyu [email protected] 1
Mining Research Institute, Inner Mongolia University of Science and Technology, Baotou 014010, China
2
College of Mining, Liaoning Technical University, Fuxin 123000, China
Rock burst is a special phenomenon caused by mining pressure and has become one of the main disasters at coal mines in China (Cai et al. 2016). Rese
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