循环载荷作用下含钻孔煤样力学响应特征实验研究

Experimental study on mechanical response characteristics of coal specimens with boreholes under cyclic loading

  • 摘要: 为探究加载速率与循环载荷作用下含钻孔煤样力学响应特征,以选自常村煤矿工作面的含钻孔煤样为研究对象,开展不同应力路径(单调加载、循环加载−卸载)及加载速率(0.5,2.0 kN/s)下的力学实验,结合非接触式全场应变测量系统和声发射(AE)监测系统,研究含钻孔煤样的强度、变形、破坏模式及裂隙演化特征。结果表明:① 与无钻孔煤样相比,设定加载路径和速率下含钻孔煤样的单轴抗压强度降低9.50%~26.24%。② 单调加载条件下,当加载速率从0.5 kN/s提高到2.0 kN/s,含钻孔煤样的单轴抗压强度增大7.70%;钻孔周围应变集中显著,高应变区呈蝴蝶形分布并沿轴向加载方向扩展,形成典型的“X”形破坏,破坏模式以拉伸破坏为主;低加载速率下裂隙呈“分散起裂−局部贯通”特征,高加载速率下裂隙被提前激活,表现为“快速扩展—突发贯通”的爆发型特征。③ 循环加载−卸载条件下,低速率加载时应变累计增幅有限,AE累计能量增长平缓;高速率加载时AE累计能量增长速率明显增大,裂隙在早期循环中贯通。研究成果可为瓦斯抽采钻孔稳定性控制及封孔工艺优化提供理论支撑。

     

    Abstract: To investigate the mechanical response characteristics of coal specimens with boreholes under different loading rates and cyclic loading, mechanical tests were conducted on coal specimens with boreholes selected from a working face of Changcun Coal Mine under different stress paths (monotonic loading and cyclic loading–unloading) and loading rates (0.5 and 2.0 kN/s). A non-contact full-field strain measurement system and an Acoustic Emission (AE) monitoring system were used to examine the strength, deformation, failure modes, and fracture evolution characteristics of the coal specimens with boreholes. The results showed that: ① Compared with that of coal specimens without boreholes, the uniaxial compressive strength of coal specimens with boreholes decreased by 9.50%–26.24% under the specified loading paths and rates. ② Under monotonic loading, when the loading rate increased from 0.5 to 2.0 kN/s, the uniaxial compressive strength of coal specimens with boreholes increased by 7.70%. Significant strain concentration occurred around the boreholes, and the high-strain zones exhibited a butterfly-shaped distribution and extended along the axial loading direction, forming a typical X-shaped failure dominated by tensile failure. At the low loading rate, the fractures exhibited dispersed initiation and local coalescence. At the high loading rate, the fractures were activated earlier and exhibited burst-like characteristics of rapid propagation and sudden coalescence. ③ Under cyclic loading–unloading, at the low loading rate, the cumulative strain increased only slightly and the cumulative AE energy increased gradually. At the high loading rate, the AE energy growth rate increased markedly, and the fractures coalesced during the early loading cycles. These results provide theoretical support for the stability control of gas drainage boreholes and optimization of sealing processes.

     

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