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| Effect of loading rate on fracture behavior of hard roof rock in coal mine |
| CHEN Lichao1，2，WANG Shengwei2，3，ZHANG Diankun2 |
(1. School of Mining Technology，Inner Mongolia University of Technology，Hohhot，Inner Mongolia 010051，China；2. State Key Laboratory of Coal and CBM Co-mining，Jincheng，Shanxi 028204，China；3. Faculty of Earth Resources，
China University of Geosciences(Wuhan)，Wuhan，Hubei 430074，China) |
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Abstract The fracture characteristics and fracture mechanism of hard roof rock in coal mines are of key significance for the optimization of the artificial roof caving. Aiming at the hard roof coarse sandstone and gravel-bearing coarse sandstone in the Junger mining area of Inner Mongolia，the semi-circular bending samples of the rock were subjected to the loading rate of 0.35–3.78 GPa•m1/2•s－1 by using the split Hopkinson pressure bar. The dynamic fracture behavior and energy dissipation mechanism of rock under different loading rates are studied. The results show that：(1) under the impact，the fracture toughness of hard roof rock in the coal mine in the study area ranges from 0.76–3.36 MPa•m0.5. With the increase of loading rate，the fracture toughness of hard roof rock samples in the coal mine increases linearly，and the effect of loading rate on the fracture properties of hard roof rocks in the study area is significant. (2) At low loading rate，the fracture of hard roof rock is mainly simple tensile fracture，and the tensile cracks are formed parallel to the loading direction. Under medium and high loading rate，central tensile fracture and oblique shear fracture are formed in the roof sandstone. (3) With the increase of loading rate，the failure modes of hard roof rock changes from simple tensile fracture to shear-punch composite fracture，the degree of rock specimen breakage tends to be serious，and the number of fractures increases while the length decreases. (4) With the increase of loading rate，the energy absorption efficiency of hard roof rock samples during the fracture process is significantly reduced，which is disadvantageous to the realization of efficient rock breaking. (5) Due to the low loading rate，hydraulic fracturing can form a large range of rock fracturing under the same energy consumption，which is conducive to improving the fracture efficiency of hard roof in coal mine. However，due to the high loading rate，blasting has a limited range of impact crushing zone，which has certain limitations as a means of artificial roof caving of hard roof in coal mine.
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2023, Vol. 42 
