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| Three-dimensional propagation of local micro-cracks and non-linear deterioration mechanism of limestone under variable amplitude cyclic loading |
| TANG Hudan1，2，ZHU Mingli3，ZHU Zhende4#br# |
(1. School of Civil Engineering，Henan Polytechnic University，Jiaozuo，Henan 454000，China；2. Key Laboratory of Underground Engineering and Disaster Prevention of Henan Province，Henan Polytechnic University，Jiaozuo，Henan 454000，China；3. School of Energy Science and Engineering Institute，Henan Polytechnic University，Jiaozuo，Henan 454000，China；4. Geotechnical Research Institute，Hohai University，Nanjing，Jiangsu 210098，China)
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Abstract The deformation and failure process of deep rock masses is affected by excavation unloading or other disturbing loads. In order to explore the propagation law of spatial micro-cracks in rock masses and the non-linear mechanism of the progressive failure process，a three-dimensional positioning acoustic emission experiment of limestone under pre-static low-frequency unequal amplitude loading and unloading cycles was carried out. The results show that the ratios of the elastic energy and the dissipated energy to the total energy all have corresponding stage characteristics. The change of the dissipated energy is related to the distribution of the prefabricated cracks as well as the location and the expansion speed of the micro-cracks. The changes in the dissipated energy and the number of impacts satisfy the critical power law of limestone catastrophe. The peak strengths of the intact limestone specimen and the prefabricated limestone specimen with different inclination angles decrease with increasing the number of the prefabricated cracks and are affected by the position of the prefabricated cracks. The stress-strain curves of different specimens present different degrees of transition after the peak and appear type I curve and type II curve. It is also shown that the multiplicity and local propagation of three-dimensional cracks in limestone samples are affected by the prefabricated cracks，and that the failure processes of the intact samples and the samples with different prefabricated fractures are dominated by different mechanical mechanisms and show different failure modes macroscopically. On the basis of in-depth study on the rock degradation process，the calculus in the field of mathematics，the principle of thermodynamics in the field of physics and the specific problems in the field of rock mechanics and engineering are combined to reveal the nonlinear mechanism of the energy evolution process. The research results expand the depth of thermodynamic research and facilitate the understanding of the transient state thermodynamic mechanism and the non-linear breakage mechanism of the engineering rock mass degradation process.
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2021, Vol. 40 
