期刊
ROCK MECHANICS AND ROCK ENGINEERING
卷 48, 期 2, 页码 509-526出版社
SPRINGER WIEN
DOI: 10.1007/s00603-014-0602-0
关键词
Coal; Triaxial compression; Computed tomography image; Failure; Damage variable; Energy dissipation; Energy release
资金
- National Basic Research Program of China [2010CB226804, 2011CB201201]
- National Natural Science Funds for Distinguished Young Scholar of China [51125017]
- National Natural Science Foundation of China [10802092]
- Program for New Century Excellent Talents in University [NCET-12-0966]
- Fundamental Research Funds for the Central Universities [2009QM03]
Theoretical and experimental studies have revealed that energy dissipation and release play an important role in the deformation and failure of coal rocks. To determine the relationship between energy transformation and coal failure, the mechanical behaviors of coal specimens taken from a 600-m deep mine were investigated by conventional triaxial compression tests using five different confining pressures. Each coal specimen was scanned by microfocus computed tomography before and after testing to examine the crack patterns. Sieve analysis was used to measure the post-failure coal fragments, and a fractal model was developed for describing the size distribution of the fragments. Based on the test results, a damage evolution model of the rigidity degeneration of coal before the peak strength was also developed and used to determine the initial damage and critical damage variables. It was found that the peak strength increased with increasing confining pressure, but the critical damage variable was almost invariant. More new cracks were initiated in the coal specimens when there was no confining pressure or the pressure was too high. The parameters of failure energy ratio beta and stress drop coefficient alpha are further proposed to describe the failure mode of coal under different confining pressures. The test results revealed that beta was approximately linearly related to the fractal dimension of the coal fragments and that a higher failure energy ratio corresponded to a larger fractal dimension and more severe failure. The stress drop coefficient alpha decreased approximately exponentially with increasing confining pressure, and could be used to appropriately describe the evolution of the coal failure mode from brittle to ductile with increasing confining pressure. A large beta and small alpha under a high confining pressure were noticed during the tests, which implied that the failure of the coal was a kind of pseudo-ductile failure. Brittle failure occurred when the confining pressure was unloaded-an observation that is important for the safety assessment of deep mines, where a high in situ stress might result in brittle failure of the coal seam, or sudden outburst.
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