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Experimental study of propagation mode of crack in real rock#br# specimens with a single crack |
LIU Weitao1,SHEN Jianjun2 |
(1. College of Mining and Safety Engineering,Shandong University of Science and Technology,Qingdao,Shandong 266590,China;2. College of Geoscience and Surveying Engineering,China University of Mining and Technology,Beijing 100083,China) |
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Abstract In order to study the fracturing characteristics of the rock with a single crack,mechanical test was carried out to the rock specimen with a single pre-existing crack inclined at 45° using the MTS815.03 electrohydraulic servo controlled rock pressure testing machine. The confining pressure of 0,5,10 MPa were separately applied to the rock specimen and the effect on the crack propagation as well as the fracturing mode was analysed. A crack propagation model was established and the secondary cracking angle was obtained based on the maximum radial shearing stress criterion. The obvious precursory information occurred before the initial crack and the obvious stress drop was shown on the stress-strain curve. Wing cracks,secondary coplanar cracks and secondary anti-wing cracks were observed in tests. The initiation angle of wing cracks are about 68°–73°,the inclined anti-wing crack angles are about -119°–-125°.. The calculated theoretical crack angles are 0°,70.5° and -123.8°respectively which are consistent with the test results. The initiation stress is 90%–95% of the peak stress. The compressive strength and the confining pressure of fine sandstone have a good linear relationship of ?c = 2.69?3+61.9 with R2 = 0.97. The confining pressure affected fracturing. The fracturing modes are wing crack and anti-wing crack under no confining pressure,anti-wing crack under 5 MPa of confining pressure,anti-wing crack and secondary coplanar crack under 10 MPa of confining pressure.
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