Mechanical characteristics and crack evolution in specimens with double over-excavated cavities: experimental and numerical investigations
Springer Science and Business Media LLC - Trang 1-20 - 2024
Tóm tắt
The mechanically over-excavated cavity along the borehole represents an innovative technology designed to enhance permeability in soft coal seams. This study aims to elucidate the complex mechanisms that influence the mechanical properties and crack evolution of over-excavated cavities. Uniaxial compression tests were performed on coal specimens with double over-excavated cavities, and the impact of cavity length–height ratio and shape on mechanical properties and crack evolution was investigated using digital image correlation techniques and acoustic emission (AE) measurements. Discrete element method simulations provided deeper insights into stress evolution and crack behavior around the cavities. The presence of an over-excavated cavity significantly affected the specimen’s mechanical properties, with the effect’s magnitude closely linked to the length–height ratio. As this ratio decreased, the peak stress and elastic modulus of the specimen increased. Specimens containing elliptical cavities demonstrated higher elastic modulus and peak stress compared to those with rectangular cavities of the same length. Crack initiation and propagation displayed distinct features, such as a sudden surge in AE counts and the appearance of strain concentration regions. The failure mode of the specimen was dominated by shear failure combined with tensile failure, and spalling of the specimen appeared as the length–height ratio decreased, indicating stronger damage. Numerical simulations aligned well with experimental findings, revealing tensile and shear cracks as predominant, with failure resulting from crack coalescence. Specimens containing rectangular cavities were more prone to failure than those with elliptical cavities due to stress concentration in corners. The maximum compressive principal stress was concentrated at the tips of the left and right flaws. The release and transfer of stress concentration zones played a pivotal role in influencing the evolution and behavior of cracks, ultimately impacting the overall mechanical response and failure characteristics of the specimen. The research findings provide valuable insights for optimizing the parameters of mechanically over-excavated cavities in coal mines, enhancing performance and safety.
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