STUDY OF MECHANICAL PROPERTIES OF RAW COAL UNDER HIGH STRESS WITH TRIAXIAL UNLOADINGChinese Full Text
LIU Quansheng;LIU Kaide;LU Xingli;ZHU Jiebing;State Key Laboratory of Geomechanics and Geotechnical Engineering,Institute of Rock and Soil Mechanics,Chinese Academy of Sciences;Xi’an Research Institute,China Coal Technology and Engineering Group Corp;Key Laboratory of Geotechnical Mechanics and Engineering of Ministry of Water Resources,Yangtze River Scientific Research Institute;
Abstract: Based on the raw coal from B10 seam of-780 m in Huainan coal mine,unloading tests under high stress were carried out in the style of non-uniform velocity of unloading confining pressure and axial pressure synchronously,and the test results were compared with that of conventional triaxial experiments under the same confining pressure. The deformation,strength,parameters and failure characteristics of the raw coal under unloading were studied. The results show that:（1） From the unloading point,the deviatoric stress-axial strain curves pitch up abruptly,and its gradient increases. But compared with conventional triaxial curve,peak axial strain under unloading condition decreases apparently,yield process is obviously shorten and post-peak brittle failure characteristics is significant.（2） From the unloading point,the deviatoric stress- lateral strain curves fall abruptly,and its gradient decreases. The peak lateral strain is smaller than that of conventional triaxial curves. Before post-peak destroying,the stress drops slowly,and 3 changes greatly. While that of conventional triaxial curves fall rapidly,and 3 changes small.（3） From unloading point,the deviatoric stress-volume strain curves reverse left instantly,presenting the features of obvious dilatancy. And in the interval near peak point,the dilatancy is the strongest. However,except the conventional triaxial curves show dilatancy characteristics under low confining pressure conditions,the curves always extended right under high confining pressure,and presenting a continuous shrinkage state.（4） In the process of unloading,the deformation modulus E always reduces,and the damage factor D and Poissons ratio μ always increase. And the three change trend are gentle before peak,gradually increase after peak. Moreover,the E,D and μ all increase in general with the increase of initial confining pressure.（5） The failure modes of unloading coal samples are mainly shear failure,and rupture angle is in the range of 20°–32°,which increases in parabolic trend with the increase of confining pressure. Under the same initial confining pressure,the value of θ is less than that of the triaxial angle.（6） The shear strength parameters c of coal under unloading is less than that of the triaxial,and the value of is very close.
Keywords：
rock mechanics; high stress; raw coal; unloading; deformation feature; strength characteristic; failure mechanism; mechanical parameters;
- DOI：
10.13722/j.cnki.jrme.2014.s2.006
- Series：
- Subject：
- Classification Code：
TU452
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