Abstract
In this paper, the failure and fracture process of mylonite with a prefabricated circular opening under biaxial loading is studied by PFC2D code. Firstly, the hoop stress change law of opening wall in the process of loading is theoretically analyzed and three fracture patterns of rocks are proposed. Secondly, the biaxial loading tests of mylonite for numerical simulation are carried out, and the failure and fracture are analyzed from three aspects of space-time evolution of microcracks, energy conversion process, and final damage patterns. As the load progresses, the microcracks start to initiate at the side wall of the opening and the growth velocity of microcracks develops from the slow to fast and then slows down again. The final damage pattern of mylonite with a prefabricated circular opening belongs to shear fracture. The fracture zones start with the side wall spalling and then gradually extend to the border of the rock, which widen from the opening boundary to the border of the rock and slightly twist in the middle. The final fault zone width is about 6 times wider than the average size of simulation particles. Finally, based on the uniaxial compressive strength of mylonite in the laboratory, it is inferred that the fracture pattern of mylonite with a prefabricated circular opening by theoretical analysis is indeed shear failure, which is consistent with the result of numerical simulation.
Highlights
In recent years, with the continuous depletion of shallow mineral resources and global environmental agitations against mining, deep mining is becoming the development trend in the future
Roughout the experimental studies of rocks with prefabricated openings in the whole world, it is shown that under the uniaxial compression condition, the ultimate damage pattern of the rock with a circular opening mainly presents the tensile fractures at the top and bottom of the opening paralleling to the loading orientation, the compression fractures are produced on both sides of the opening, Advances in Civil Engineering and the far-field failures occurs around the opening [12, 21]
The mylonite is taken as the research object, and the failure and fracture process of mylonite with a prefabricated circular opening is researched under the biaxial loading condition by PFC2D. e simulated results are analyzed from three aspects: space-time evolution of microcracks, energy conversion process, and the final fracture patterns
Summary
With the continuous depletion of shallow mineral resources and global environmental agitations against mining, deep mining is becoming the development trend in the future. Erefore, laboratory and numerical simulation tests for small-sized rocks have become the mainstream to study the damage mechanism of rock mass around underground excavation [19, 20]. Compared with the physical experiment in the laboratory, numerical simulation can reproduce the failure evolvement of rocks during the loading process, and it can be used to analyze the failure and fracture mechanism of rocks from different aspects and the numerical simulation tests can be repeated to generate the reliable results [11, 21, 22]. E particle flow code PFC2D based on the DEM can well simulate the local anisotropic behaviors of rocks during the loading process and can reproduce the space-time evolution of microcracks and the eventual fracture zones so which is widely adopted to study the mechanical behaviors of various of rock mass [24] which utilized PFC2D to predict the fracture zones of the Canadian underground laboratory. The mylonite is taken as the research object, and the failure and fracture process of mylonite with a prefabricated circular opening is researched under the biaxial loading condition by PFC2D. e simulated results are analyzed from three aspects: space-time evolution of microcracks, energy conversion process, and the final fracture patterns
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