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.

沿钻孔的机械超挖空腔代表了一项旨在提高松软煤层渗透性的创新技术。本研究旨在阐明影响超挖空腔力学性能和裂纹演化的复杂机制。对双超挖空腔煤样进行单轴压缩试验，利用数字图像相关技术和声发射（AE）测量研究空腔长高比和形状对力学性能和裂纹演化的影响。离散元方法模拟可以更深入地了解空腔周围的应力演变和裂纹行为。过度挖掘空腔的存在显着影响了样本的机械性能，其影响程度与长高比密切相关。随着该比率的降低，样品的峰值应力和弹性模量增加。与具有相同长度的矩形腔体的样本相比，包含椭圆形腔体的样本表现出更高的弹性模量和峰值应力。裂纹萌生和扩展表现出不同的特征，例如 AE 计数突然激增和应变集中区域的出现。试件的破坏模式以剪切破坏与拉伸破坏相结合为主，随着长高比的减小，试件出现剥落，破坏程度更强。数值模拟与实验结果非常吻合，表明拉伸和剪切裂纹是主要裂纹，裂纹合并导致失效。由于角落处的应力集中，包含矩形腔的样本比椭圆形腔的样本更容易发生故障。最大压主应力集中在左右裂纹尖端。应力集中区的释放和转移在影响裂纹的演化和行为方面发挥着关键作用，最终影响试件的整体力学响应和失效特征。研究结果为优化煤矿机械超挖空腔的参数、提高性能和安全性提供了宝贵的见解。