Research into the effects of micromechanical parameters on creep failure in brittle rocks
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ORIGINAL PAPER
Research into the effects of micromechanical parameters on creep failure in brittle rocks X. Z. Li & Z. S. Shao & X. Y. Wang
Received: 24 March 2014 / Accepted: 22 December 2014 # Saudi Society for Geosciences 2015
Abstract Subcritical crack growth plays an important role for long-term creep failure in brittle rock. Microcrack angle is a significant parameter in theoretical analysis. However, it is difficult to be obtained from test or theory. Based on micromechanical creep theory of brittle rock which is established by using of relationship between micromechanical crack growth and macroscopic strain, effects of the value of microcrack angle on creep property of brittle rock with given initial damage are investigated in this paper. Based on the theoretical model and testing results, an exact method to determine the reasonable value of microcrack angle in a given rock specimen is suggested. Using this determined crack angle, further creep analysis of brittle rock is carried out, and all numerical results are graphically presented. As verification, the comparison of irreversible strain between theoretical and experimental results shows a good agreement. Keywords Brittle creep . Damage . Microcrack angle . Crack growth
Introduction For underground engineering with brittle surrounding rock, spalling or disruption of concrete supporting structure sometimes occurs during its long-term service. This failure phenomenon is due to the creep deformation of brittle rock with initial microcracks. The chemical influence of pore water promotes the subcritical crack growth. Subcritical crack growth X. Z. Li : Z. S. Shao (*) : X. Y. Wang School of Civil Engineering, Xi’an University of Architecture & Technology, Xi’an 710055, China e-mail: [email protected]
allows rocks to gradually deform and finally fail at stresses well below their short-term failure strength and even at constant applied stress (“brittle creep”). With the rapid development of underground engineering, brittle creep failure in rocks attracts more and more interests of scholars around the world. It is well known that the macroscopic creep failure of brittle rock is initially resulted in the microcrack growth under long-term external actions. According to the crack evolution, creep in brittle rock is generally divided into transient creep, stationary creep, and accelerated creep. Scholz (1968) firstly considered the creep in brittle rock which is due to time-dependent cracking at low temperature. He derived the transient creep law from mechanism of time-dependent cracking in nonhomogeneous brittle material. He also predicted the stress dependence of creep by using this theoretical model. Based on Scholz’s theory and the Charles’s law, Cruden (1970) studied the effect of micromechanical parameters on creep behavior in brittle rock subjected uniaxial compress loading. Cocks and Ashby (1982) theoretically studied the creep fracture. They found that, over a wide range of stress and temperature, voids grow predominantly by diffusion when they are
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