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不同层理倾角下NPR加锚煤岩复合岩样破坏机制及临界慢化前兆试验研究

Failure mechanism and critical slowing down precursor of NPR anchored coal-rock composite specimens under different bedding dip angles

  • 摘要: 为揭示层理倾角与锚固类型对煤岩复合体破坏机制及失稳前兆特征的影响,针对15°、30°、45°层理倾角的煤岩组合体,开展无锚、PR锚杆、NPR锚杆加锚条件下的单轴压缩试验,采用声发射仪与CCD相机监测,分析复合岩样的破坏模式、峰值强度及声发射能率演化特征。基于临界慢化理论,创新地提出加权波动不对称度、平均绝对偏差特征指标,明确前兆指标的出现时序规律,探究层理倾角与不同锚固条件对临界慢化特征及预警时机的影响。试验结果表明:15°~45°试验范围内,层理倾角增大会使煤岩复合岩样的破坏模式由拉剪复合破坏向剪切破坏转变,且破坏程度加剧,声发射能率峰值升高,锚杆支护效果减弱;相同层理倾角,NPR锚杆加锚岩样的破坏程度最低、峰值强度最高,声发射能率峰值较无锚、PR 锚杆加锚岩样分别降低62.50%~83.34%、27.28%~46.22%。PR、NPR锚杆加锚岩样的声发射能量临界慢化前兆信息呈相同规律,先后顺序为加权波动不对称度>恢复率>平均绝对偏差>方差,在15°~45°试验范围内,多数前兆指标的前兆点与破坏点时间比值总体随人工胶结界面倾角增大而降低,其中45°试样的前兆指标整体出现较早。与PR锚杆相比,NPR锚杆约束试样的加权波动不对称度和恢复率在多数工况下较早出现前兆响应。加权波动不对称度能够弥补传统临界慢化指标难以反映系统早期失稳前兆的不足,可作为表征煤岩复合岩样初始损伤的有效早期预警参数。研究成果明确了加锚煤岩复合体系的失稳前兆演化规律,为深部煤岩互层复杂构造区域围岩失稳灾害的早期预警与防控提供了理论依据。

     

    Abstract: To reveal the influences of bedding dip angle and anchorage type on the failure mechanism and instability precursor characteristics of coal-rock composite specimens, uniaxial compression tests were carried out on coal-rock combinations with bedding dip angles of 15°, 30° and 45° under unreinforced, PR bolt-reinforced and NPR bolt-reinforced conditions. Acoustic emission (AE) instruments and CCD cameras were used to monitor the failure mode, peak strength and evolution characteristics of AE energy rate of the composite specimens. Based on the critical slowing-down theory, two characteristic indicators, i.e., weighted fluctuation asymmetry and mean absolute deviation, were innovatively proposed. The occurrence sequence of precursor indicators was clarified, and the influences of bedding dip angle and different anchorage conditions on the critical slowing-down characteristics and early-warning timing were investigated. Within the investigated range of 15°–45°, increasing the interface inclination changes the failure mode of coal-rock composite specimens from tensile-shear composite failure toward shear-dominated failure, accompanied by increased failure severity, higher peak AE energy rate, and a reduced relative restraining effect of the bolts. At the same bedding dip angle, the NPR bolt-reinforced specimens exhibit the lowest failure degree and the highest peak strength. The peak AE energy rate of NPR bolt-reinforced specimens is reduced by 62.50%–83.34% and 27.28%–46.22% compared with unreinforced and PR bolt-reinforced specimens, respectively. The AE energy critical slowing-down precursors of PR and NPR bolt-reinforced specimens present the same evolution law, with the sequence of weighted fluctuation asymmetry > recovery rate > mean absolute deviation > variance. Within the investigated range of 15°–45°, most precursor-to-failure time ratios generally decreased with increasing interface inclination, and the precursor responses of the 45° specimens appeared relatively earlier. Compared with PR bolts, the weighted fluctuation asymmetry and recovery rate of NPR bolt-reinforced specimens generally exhibited earlier precursor responses under most investigated conditions. The weighted fluctuation asymmetry makes up for the shortcoming that traditional critical slowing-down indicators are difficult to reflect the early instability precursors of the system, and can be used as an effective early-warning parameter to characterize the initial damage of coal-rock composite specimens. The research results clarify the instability precursor evolution law of anchored coal-rock composite system, which provides a theoretical basis for the early warning and prevention of surrounding rock instability disasters in deep complex structural areas with coal-rock interbeds.

     

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