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含不同角度预制孔类岩石试样单轴压缩渐进破坏规律

Progressive failure law of rock with prefabricated holes of different angles under uniaxial compression

  • 摘要: 钻孔失稳、孔壁垮落及裂隙错位是导致瓦斯抽采钻孔失效的主要原因。为研究瓦斯抽采钻孔倾角对围岩承载特性及稳定性的影响, 对不同角度钻孔围岩力学特性及破坏特征进行系统研究。采用类岩石材料制备含0°、30°、60°、75°、90°预制孔试样开展单轴压缩试验, 运用岩石刚性试验机、声发射监测系统、应变测量系统(DIC)及超高清钻孔窥视仪同步观测围岩变形破裂特征。结果表明: ①预制孔导致试样峰值强度与弹性模量降低, 其中60°倾角试样峰值强度降幅最大(较完整试样降低30.48%); ②加载过程中试样能量突增模式与预制孔角度存在相关性, 90°试样二次能量释放量达75.8 V·ms; ③张拉破坏为主要破坏形式, 其占比由0°时的70.6%降至90°时的51.4%, 但随着倾角增大剪切破坏占比逐步提升; ④孔壁围岩承载能力随倾角增大呈递增趋势, 孔内裂隙萌生较试样外表面显著滞后, 其破坏时刻与声发射能量突增时点具有一致性; ⑤预制孔角度的增大, 使得试样内力及裂纹分布由孔壁两侧集中转为四周均匀分布, 体现了钻孔围岩承载能力的提高。研究成果可为揭示瓦斯抽采钻孔围岩变形破坏规律及优化钻孔布置方式提供理论参考。

     

    Abstract: Borehole instability, wall collapse and fracture misalignment are the primary causes of borehole failure in gas drainage. To investigate the influence of borehole inclination angle on the load-bearing characteristics and stability of surrounding rock, experiemental study was conducted on the mechanical properties and failure characteristics of surrounding rock with boreholes at different angles. Uniaxial compression tests were conduced on rock-like specimens with prefabricated holes at 0°, 30°, 60°, 75°, and 90° to the horizon. A rock rigidity testing machine, acoustic emission (AE) monitoring system, digital image correlation (DIC) strain measurement system and ultra-high-definition borehole inspection camera were used to study the deformation and fracture behavior of the surrounding rock. The results show that the prefabricated holes reduce the peak strength and elastic modulus of the specimens, with the 60° inclined specimen exhibiting the greatest strength reduction (30.48% lower than the intact specimen). The energy surge pattern during loading correlates with the borehole inclination angle, with the 90° specimen showing a secondary energy release of 75.8 V·ms. Tensile failure dominates, accounting for 70.6% at 0° but decreasing to 51.4% at 90°, while shear failure gradually increases with inclination angle. The load-bearing capacity of the borehole wall increases with the inclination angle, and crack initiation inside the hole lags significantly behind the specimen surface, with failure timing coinciding with AE energy surges. As the borehole angle increases, internal stress and crack distribution shift from concentration at both sides of the hole to a more uniform circumferential distribution, reflecting enhanced load-bearing capacity. The findings help understanding the deformation and failure mechanism of surrounding rock of gas drainage borehole and optimizing borehole layout design.

     

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