Meikuang Anquan (Oct 2023)
Study on bump-prone property of coal under multi-stage confining pressure variable stress lower limit cyclic loading and unloading
Abstract
The study of coal bump-prone property under confining pressure plays a key role in exploring the formation mechanism of coal burst in deep underground mines. In order to explore the influence of different confining pressures on bump-prone property of coal, this paper carried out cyclic loading and unloading of coal with different stress lower limits under multistage confining pressures. The test results show that: under the confining pressure environment of 3 MPa, 6 MPa and 9 MPa, the compressive strength of coal specimens increased by 3.1%, 4.7% and 6.2% respectively after cyclic loading and unloading, and the axial strain increased by 0.61%, 0.42% and 0.28% respectively in the last stage of cyclic loading and unloading. The volumetric strain increases by 0.32%, 0.24% and 0.17%, respectively, indicating that the larger the confining pressure is, the stronger the deformation constraint is. With the increase of confining pressure, the cumulative number of AE events gradually decreases, the cumulative number of AE after peak continuously decreases, and the cumulative energy also gradually decreases, indicating that with the increase of confining pressure, the coal specimen becomes more compact, and the failure mode gradually transitions from brittle failure to ductile failure. In addition, after the confining pressures of 3 MPa, 6 MPa and 9 MPa, the input energy \begin{document}$U_{{\rm{in}}}^{\rm{n}} $\end{document} and elastic strain energy \begin{document}$U_{\rm{e}}^{\rm{n}} $\end{document} increase continuously. Compared with the normal pressure condition, the residual elastic energy index (CEF) of coal specimens is increased by 21.76%, 42.92% and 71.69%, respectively, indicating that confining pressure has an enhanced effect on the bursting tendency of coal, and the residual elastic energy index (CEF) has a linear function relationship with confining pressure σ3.
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