煤样单轴压缩时滞性变形破坏的试验研究

在深埋中等坚硬煤层采掘工作面煤壁片帮大多表现出明显时滞性，针对采掘工作面煤壁片帮发生时滞性应力特征，在RMT-150B岩石力学试验系统上进行煤样单轴压缩和分级加载对比试验，分析两种加载方式下煤样时滞性变形破坏特征，结果表明：两种加载方式在煤样峰值前应力-应变曲线宏观没有明显区别，单轴压缩峰值后出现分次应力跌落，而分级加载最后一级应力高于煤样屈服强度时没有明显峰值点，出现屈服平台，峰值后应力跌落迅速；单轴压缩得到的力学参数明显高于分级加载试验值，表现出煤样的力学参数具有时滞性；分级加载应力比低于70%时，煤样轴向和环向变形特征不明显，分级加载应力比高于70%时，尽管轴向应力保持恒定，随着时间延长煤样轴向和环向变形则不断增加，且环向应变远大于轴向应变，体积不断增加，在此期间，煤样继续吸收外界能量内部材料逐步损伤破坏，新生微裂纹不断演化、发展和汇聚，分级加载应力水平比越高，延时破坏越短，相反延时破坏则越长，分级加载时表现出明显时滞性特征；单轴压缩时煤样破坏相对简单，具有明显张剪性双重破裂面，而分级加载时煤样破碎充分，破坏形式复杂，环向膨胀特征明显，与采掘工作面煤壁延时片帮破坏特征极为相似。其研究结果对采掘工作面煤壁延时片帮治理具有一定的参考意义。

Experimental study of time-lag deformation and failure properties of coal under uniaxial compression

The spalling of deep-buried medium hard coal wall often presents obvious time-lag characteristics. In order to analyze deformation and failure features of coal, uniaxial compressive and step loading tests are carried out on coal samples using a testing system RMT-150B. Experimental results indicate that the pre-peak stress-strain curves of two loading modes are similar, but the post-peak stress drops gradually under uniaxial compression. There is no obvious peak when final level stress is higher than yield strength of coal samples, then a yielded platform appears and the post-peak stress-strain curve has a rapid drop. Mechanical parameters obtained by uniaxial compression tests are significantly higher than that obtained by step loading tests. It is shown there are time-lag characteristics, but the axial and circumferential deformations of coal samples have no obvious characteristics when the loading stress ratio is lower than 70%. Although the axial stress force is a constant value, the axial and circumferential deformations increase gradually when the loading stress ratio is higher than 70%. The circumferential strain is far greater than the axial strain, and the volume also increases. Coal samples absorb energy, and then new microcracks are evolved, developed and assembled, which thus results in gradually damaged internal structure. The higher the step loading stress level is, the shorter the time of delayed damage is and vice versa. Therefore, the stress-strain relationships of coal samples present obvious time-lag characteristics. The failure of coal is relatively simple under uniaxial compression, which has obvious tensile-shear fracture plane. However, the coal is broken completely under step loading, the failure is complex and circumferential expansion feature is obvious. It is similar to the time-lag characteristic of coal wall spalling in the working face. The research results provide some references for the control of coal wall time delay in the mining face.