| Artificial pillar consists of cemented waste rock backfills. Artificial pillar is mainly subjected to impact load and graded constant load in practical engineering. Study on the damage regularity and failure phenomenon of cemented waste rock backfills during these two kinds of loads will very meaningful.The research mainly on graded creep load acoustic emission (AE) tests and cyclic load and unload AE tests of cemented waste rock backfills was financially supported by Nation Science Foundation of China (No.51304083). In this paper, deformation and acoustic emission (AE) characteristics of cemented waste rock backfills during these two kinds of loads was first analysed. Then, by introducing the parallel-bonded stress corrosion, the creep process by different time length of cemented waste rock backfills with different cement/tail ratio was simulated by PFC. Finally, based on the results of tests and simulation, a non-stationary nishihara model was established to describe the creep process of cemented waste rock backfills.The results show that:(1) Shear failure (type I) and tensor failure (type II) are two kinds of failure modes of cemented waste rock backfills with uniaxial strss. The two kinds of specimens both have volume deformation stage and constant volume stage during graded constant load, but only the specimens of type II have dilatancy stage. Waste rock horizontal displacement comes from the more parallel shear bond damage. The stage of strain increasing suddenly comes from the first separation between some parts of waste rocks. Creep process is described by a non-stationary nishihara model. (2) The fluctuation of b-value is like upward serration as the two kinds of specimens are in steady creep stage before the specimen failure. The Shear failure specimen in tertiary creep stage b-value of acoustic emission shows a circulation pattern that is "upward serrated fluctuation with decreased intensity". This feature indicates that the macro slip surface is formed in the process of continuous coalescence of micro cracks, which leads to the failure of the specimen. The tensor failure specimen in tertiary creep stage b-value of acoustic emission shows a continuing upward serrated fluctuation with increased amplitude. This feature indicates that the waste rocks in specimen are separated from each other. (3) In the process of loading, when the relative stress level is relatively small, the b value of AE is the trend of the overall increase, which shows that the micro-fracture in the specimen is mainly based on small scale extent. When the relative stress level becomes higher, the b value of AE is the trend of the overall decrease, which shows that the micro-fracture in the specimen is mainly based on large scale extent. The change of B value before the specimen failure is "decrease-stability-decrease", which shows that the failure caused by the connection of the micro-cracks on large scale extent. In the initial stage of unloading, the b value of AE fluctuates violently, which shows that there is still a dramatic expansion of micro-cracks in the specimen. With the decrease of the stress, the amplitude of the b value of AE is becoming smaller and smaller, which shows that the expansion of the micro rupture is gradually stopped. (4) For the multiphase composite materials of cemented waste rock backfills, before loading, the internal already contains many different kinds of micro-crack, micro-holes and uneven microstructure. Even under the low stress, the low strength of the microscopic defects will also be cracked. Therefore, during cyclic loading and unloading, cemented waste rock backfills will appear obvious Felicity effect, the effect of the range of the relative stress level of 28.1%-33.9% and more than 75.3%. |
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