Abstract
Rock excavation has experienced complex stress paths. The development of the original crack under the path of principal stress magnitude and principal stress direction is a key scientific problem that needs to be solved in rock underground engineering. The principal stress magnitude dominates the initiation and propagation of the crack and increases rock damage under the action of principal stress rotation. In this study, the theoretical calculation and numerical analysis method have been combined with the crack propagation conditions to study the stress-driven mechanism of brittle rock crack propagation under principal stress rotation. The results show that the “relative initial angle” of crack angle is being updated in time during the principal stress rotation process; once the stress is rotated, it will become the next initial crack angle; the crack propagation direction is deviated under the applied shear load, and it is always in the direction of minimum shear load, leading to a certain degree of inhibition of crack propagation depth in the initial direction. According to the results of numerical simulation, the effect of principal stress rotation caused by mining excavation is obvious and has a certain range of influence depth, the stress of surrounding rock of roadway is the highest within the depth range of 1∼2 m, and the maximum principal stress is as high as 26.89 MPa. The rotation of principal stress direction on the roadway surrounding rock surface is the strongest, which makes the surrounding rock more fragmented, and the middle principal stress and the maximum principal stress rotate about 90° counterclockwise along the Ox axis. Studying the action mechanism of principal stress rotation on fractured rock masses can provide scientific basis for geotechnical engineering design and rock mass surrounding support.
Highlights
Fractured rock mass is the main occurrence form of rock mass in nature, its strength and deformation failure are significantly affected by the generation and expansion of cracks, and the mechanical behavior of rock mass changes with the change of stress paths [1,2,3]
Because of the influence of engineering disturbance, in situ stress state changes the stress magnitude, and the rotation of the principal stress direction, which is an important factor in the research of inducing rock mass stress concentration and rock strength degradation. e excavation of rock mass in underground engineering can cause the surrounding rock stress in the excavation direction, resulting in the stress state of the fracture surface changing from the compressive shear stress state to the tensile shear stress state
Sun et al [12] investigated the influence of the fissure morphology on the dynamic mechanical properties of the rock and the crack propagation, and a drop hammer impact test device was used to conduct impact failure tests on sandstones with different fissure numbers and fissure dips, simultaneously recording the crack growth after each impact. e box fractal dimension is used to quantitatively analyze the dynamic change in the sandstone cracks, and a fractal model of crack growth over time is established based on fractal theory
Summary
Fractured rock mass is the main occurrence form of rock mass in nature, its strength and deformation failure are significantly affected by the generation and expansion of cracks, and the mechanical behavior of rock mass changes with the change of stress paths [1,2,3]. Meng et al [16], based on FLAC3D numerical analysis, discussed the distribution characteristics of stress concentration, fracture expansion, and time-dependent deformation of the surrounding rock of the cavern groups, and the formation mechanism of deep deformation is explained. Zhou et al [18] used friction sliding crack model to study the microcrack damage mechanism of brittle rock under rotation of the principal stress axes, and through the uniaxial compression test of preexisting cross-embedded cracks, the main difference between 2D and 3D cracking behavior of preexisting cracks is discussed, and the further propagation of extended wing crack leads to the ultimate failure of the specimen. On the basis of previous studies, the plane and nonplane propagation mechanisms of cracks are theoretically analyzed, and the evolution law of surrounding rock stress and the evolution characteristics of surrounding rock plastic zone during tunnel excavation are analyzed by numerical simulation
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