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Geomechanics and Engineering
  Volume 30, Number 5, September10 2022 , pages 401-411
DOI: https://doi.org/10.12989/gae.2022.30.5.401
 


Dynamic failure features and brittleness evaluation of coal under different confining pressure
Xiaohui Liu, Yu Zheng, Qijun Hao, Rui Zhao, Yang Xue and Zhaopeng Zhang

 
Abstract
    To obtain the dynamic mechanical properties, fracture modes, energy and brittleness characteristics of Furong Baijiao coal rock, the dynamic impact compression tests under 0, 4, 8 and 12 MPa confining pressure were carried out using the split Hopkinson pressure bar. The results show that failure mode of coal rock in uniaxial state is axial splitting failure, while it is mainly compression-shear failure with tensile failure in triaxial state. With strain rate and confining pressure increasing, compressive strength and peak strain increase, average fragmentation increases and fractal dimension decreases. Based on energy dissipation theory, the dissipated energy density of coal rock increases gradually with growing confining pressure, but it has little correlation with strain rate. Considering progressive destruction process of coal rock, damage variable was defined as the ratio of dissipated energy density to total absorbed energy density. The maximum damage rate was obtained by deriving damage variable to reflect its maximum failure severity, then a brittleness index BD was established based on the maximum damage rate. BD value declined gradually as confining pressure and strain rate increase, indicating the decrease of brittleness and destruction degree. When confining pressure rises to 12 MPa, brittleness index and average fragmentation gradually stabilize, which shows confining pressure growing cannot cause continuous damage. Finally, integrating dynamic deformation and destruction process of coal rock and according to its final failure characteristics under different confining pressures, BD value is used to classify the brittleness into four grades.
 
Key Words
    average fragmentation; brittleness index; dissipated energy density; maximum damage rate; split Hopkinson pressure bar
 
Address
Xiaohui Liu: Key Laboratory of Fluid and Power Machinery, Ministry of Education, Xihua University, Chengdu, 610039, China; School of Energy and Power Engineering, Xihua University, Chengdu, 610039, China; Key Laboratory of Deep Earth Science and Engineering, Sichuan University, Ministry of Education, Chengdu, 610065, China
Yu Zheng: Southwest Municipal Engineering Design & Research Institute of China, Chengdu, 610081, China
Qijun Hao: Key Laboratory of Deep Earth Science and Engineering, Sichuan University, Ministry of Education, Chengdu, 610065, China
Rui Zhao: Key Laboratory of Fluid and Power Machinery, Ministry of Education, Xihua University, Chengdu, 610039, China; School of Energy and Power Engineering, Xihua University, Chengdu, 610039, China
Yang Xue: CHN Energy Dadu River Hydropower Development Co., Ltd, Chengdu 610041, China
Zhaopeng Zhang: Key Laboratory of Deep Earth Science and Engineering, Sichuan University, Ministry of Education, Chengdu, 610065, China
 

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