| Abstract:Rock is typical inhomogeneous brittle material with abundant various deficiencies such as micro-cracks, gaps and joints. The cracks propagation process and unstable failure of rock are similar to earthquake. Therefore seismology theory can be introduced to study the rock fracture process. If it regards acoustic emission during rock fracture as mini-earthquake, rock facture process can be seen as a series completely independent earthquake. In this paper, load/unload response ratio theory and damage mechanics were applied to established mathematic model which adapt to the relationship between acoustic emission and damage during rock failure process under cycling loading. Based on the mathematic model, rock damage process and precursory characteristics under cycling loading were studied. In addition, elastic energy accelerating release(AER) process during rock fracture was study based on critical point hypothesis. At the same time, numerical simulation by RFPA2D was carried out to analysis influence of confining stress and heterogeneity to elastic accelerating energy release process. Some significant conclusions were achieved.(1) Acoustic emission can reflect the rock damage process. Under cycling loading, rock damage and AE events in unload phase is increasing more quickly than load phase with load increasing. The Y value of acoustic emission load/unload ratio descending gradually. For most rock specimens, the Y values of acoustic emission load/unload ratio reach 1 and fluctuating in small range when rock in final elastic deformation.(2) Elastic energy appears accelerating release during rock fracture process. Parameter z of power-law fitting curve, the ratio r of power-law fitting and liner fitting are less than 1 greatly. Elastic energy accelerating release in marble is more obviously than granite due to the homogeneous is better.(3) Numerical simulation results shown that bigger heterogeneity and higher confining pressure would result in more obviously power-law accelerating energy release phenomena, whereas elastic energy approaches linear release. (4) The Y value of acoustic emission load/unload ratio descend to 1 when rock reach final elastic deformation can be seen as precursory characteristic for rock failure. Elastic accelerating energy release reflects the evolutionary process and correlation length increasing of micro-cracks during rock failure. Numerical simulation results are support the seismology theory. Therefore elastic accelerating energy can also be seen as precursory characteristic of rock failure and earthquake. Through study on AER parameters z, rock failure time can be calculated. |
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