The performance of soundless cracking agents for weakening rock roof under different notch angles
The performance of soundless cracking agents for weakening rock roof under different notch angles
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DOI：
10.1007/s12517-019-4522-x
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发表时间：
2019-06-01
影响因子：
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通讯作者：
Dong, Ruowei
中科院分区：
文献类型：
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作者：
Wu, Shangjian;Zhai, Cheng;Dong, Ruowei
针对煤层硬岩顶板强度大、冒落困难等问题，主要采用传统的高压注水和深孔爆破弱化顶板的方法来改变顶板岩层的力学特性和受力状况。然而，这些方法也存在操作不便、密封要求严格以及潜在的动态危害等问题。与传统的弱化模式不同，本研究采用基于无声裂纹技术的声发射（AE）和静态应变测试系统，研究了类似岩石的材料在45度、60度、90度、120度和135度五个不同缺口角度下的裂纹扩展及其相互影响。在此基础上，进一步研究了不同缺口角装药孔对煤层顶板动态裂纹扩展的影响。研究结果揭示了5个关键点：一是在无声裂缝剂水化膨胀作用下，试样经过裂纹起裂、扩展和开裂阶段的先后变化，最终形成宏观断裂面；随着预制缺口角的增大，起爆角逐渐减小，当预制缺口角为45°时起爆角最大，为82°；第三，与未加预制缺口的试件相比，预制缺口试件的分形维数更大。分形维数与裂缝密度、裂缝数量、裂缝宽度呈正相关。(4)预制缺口试件的累积衰落次数和累积能量均大于未预制缺口试件。是1-2次。缺口角越小，累积衰荡数和累积能量越大。缺口角度与断裂程度呈负相关关系，预制缺口试件整体开裂效果最好，缺口角度为45度时试件破碎程度最好。该研究可在一定程度上为弱化煤层顶板提供理论支持。
Aiming at the problems with hard rock roof of coal seams, such as their large strength and difficulty in caving, traditional high-pressure water injection, and deep-hole blasting methods for roof weakening are mainly used to change mechanical characteristics and conditions of roof strata. However, these methods are not free from problems, such as inconvenience operation, strict sealing requirement, and potential dynamic hazards. Differing from the traditional weakening modes, this study investigated the crack propagation in materials similar to rocks and mutual influences thereon at five different notch angles (45 degrees, 60 degrees, 90 degrees, 120 degrees, and 135 degrees) by using acoustic emission (AE) and static strain test system based on the soundless cracking technology. On this basis, the study further investigated the effect of the charging holes with different notch angles on dynamic crack propagation in coal seam rock roof The results revealed five key points: firstly, macroscopic fracture surfaces were finally formed in the specimens after successively undergoing crack initiation, propagation, and cracking phases under the effect of hydration swelling of soundless cracking agent (SCA). Secondly, the initiation angle reduced with increasing prefabricated notch angle and it was at a maximum (82 degrees) when the notch angle was 45 degrees. Thirdly, compared with the specimens without prefabricated notches, the specimens with prefabricated notches exhibited a larger fractal dimension. The fractal dimension was positively correlated with the density, quantity, and width of fractures. Fourthly, the cumulative ring-down counts and cumulative energies of specimens with prefabricated notches are both larger than those without prefabricated notches. It is 1-2 times. The smaller the notch angle was, the larger the accumulative ring-down counts and cumulative energy. Fifthly, the notch angle was negatively correlated with the fracture degree as evinced by specimens with prefabricated notches showing best overall cracking effect and the fragmentation of sample when the notch angle was 45 degrees. The study can provide theoretical support for weakening coal seam rock roof to some extent.