我国矿井瓦斯灾害较为严重，其防治措施之一是井下顺层钻孔抽采瓦斯，由于顺层钻孔易变形、坍塌失稳，影响瓦斯抽采效率。同时，工作面前方煤体在采动影响下经历周期性载荷作用，使得钻孔变形失稳机理更加复杂。基于煤矿现场顺层瓦斯抽采钻孔变形破坏特征，本文采用力学实验、理论分析与现场验证相结合的研究方法，运用光学散斑及声发射相关技术研究不同加载路径下钻孔变形破坏特征及损伤演化规律。

首先，采用光学散斑技术(XTDIC)监测试样表面裂纹演化特征及孔周位移演化规律，发现试样在不同加载速率、不同加载路径影响下，其破坏模式均为拉剪复合破坏，破坏形状呈“X”状，不同加载路径下各测点位移值均与加载速率呈负线性关系。

其次，通过声发射监测并结合试样强度特征对含孔试样内部损伤演化进行分析，得到加载速率越大，峰值能量、峰值计数及抗压强度越大。循环加卸载路径下，Felicity比随着加载速率增大而增大，声发射累计计数曲线呈“台阶式”增长，与应力相比有一定的滞后性。

最后，通过对循环加卸载路径下钻孔孔周的应力情况进行分析，得到加载速率越大，钻孔顶部切向应力越小，破坏范围越小。而加载速率越大，孔帮附近切向应力越大，破坏越大。基于加卸载响应比理论研究循环加卸载试样破坏前兆信息，明确试样损伤特性的加载路径效应，与单调加载试样相比，循环加卸载路径下抗压强度、峰值能量、峰值计数出现不同程度降低。

本文研究成果揭示了不同加载路径、加载速率影响下含钻孔型煤试件的失稳机理，对煤矿现场本煤层预抽钻孔布置有一定的指导意义，为煤与瓦斯高效共采提供一定的理论依据。

One of the prevention and control measures for the more serious gas disasters in China's mines is the extraction of gas from down-hole cascade boreholes, which are prone to deformation and collapse instability, affecting the efficiency of gas extraction. At the same time, the coal in front of the working face undergoes cyclic loading under the influence of mining, making the deformation and destabilisation mechanism of the borehole more complex. Based on the deformation and damage characteristics of cascade gas extraction boreholes in coal mines, this paper uses a combination of mechanical experiments, theoretical analysis and field verification to study the deformation and damage characteristics and damage evolution of boreholes under different loading paths using optical scattering and acoustic emission related techniques：

Firstly, optical scattering technique (XTDIC) was used to monitor the crack evolution characteristics on the surface of the specimen and the evolution of the perimeter displacement of the hole. It was found that under the influence of different loading rates and different loading paths, the damage mode of the specimens were all tensile-shear composite damage, the damage shape was "X", and the displacement values of each measurement point under different loading paths were all negatively linearly related to the loading rate.

Secondly, the internal damage evolution of the specimens containing holes was analysed by acoustic emission monitoring and combined with the strength characteristics of the specimens. The higher the loading rate, the higher the peak energy, peak counts and compressive strength. In the cyclic loading and unloading path, the Felicity ratio increases with increasing loading rate and the cumulative acoustic emission count curve increases in a "stepwise" manner, with a certain hysteresis compared to the stress.

Finally, by analysing the stresses around the perimeter of the borehole under the cyclic loading and unloading path, it was found that the higher the loading rate, the lower the tangential stresses at the top of the borehole and the smaller the damage. The higher the loading rate, the higher the tangential stresses around the hole gang, and the greater the damage. Based on the response ratio theory of loading and unloading, the damage precursor information of cyclic loading and unloading specimens was studied to clarify the loading path effect of the damage characteristics of the specimens. Compared with the monotonically loaded specimens, the compressive strength, peak energy and peak count were reduced to different degrees under the cyclic loading and unloading path.

The research results of this paper reveal the destabilisation mechanism of coal specimens containing boreholes under the influence of different loading paths and loading rates. It is a guide to the arrangement of pre-sumping boreholes in coal seam at the coal mine site, and provides a theoretical basis for efficient co-mining of coal and gas.

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