不同卸围压速率下煤样卸荷破坏能量演化特征

岩体破坏实际上是在能量驱动下的一种状态失稳现象,其变形破坏过程中的能量演化规律能够反映岩体变形破坏的本质特征。为探求煤样破坏过程中能量的演化规律,对其进行了常规三轴及不同卸围压速率的三轴卸围压试验。试验结果表明:不同试验路径下,煤样在峰值应力前以能量的存储及耗散为主,在峰值应力后以能量的释放及耗散为主;煤样在较高的卸围压速率下,卸荷段经历时间较短,内部裂纹扩展及环向变形不充分,耗散能和克服围压做功耗能都较小,大量的能量在破裂时释放出来,破裂更加剧烈;同时,卸围压速率越快,煤样在破裂前后损伤量增加速率越快,损伤曲线急剧增高,因此,高应力煤岩体在开挖卸荷时,在岩体开挖施工速度较快时,极易引起大量积聚能量的突然释放,造成严重的灾害。

Energy evolution characteristics of coal failure in triaxial tests under different unloading confining pressure rates

Rock damage is considered as a state of instability phenomenon under the driving of energy, the law of energy evolution in the process of deformation and failure can reflect the essential characteristics of rock mass deformation and failure. The loading and unloading tests were carried out on coal samples to explore the laws of energy evolution under different unloading confining pressure rates. The experimental results show that before the peak stress, the coal sample mainly experiences the energy storage and dissipation, whereas it mainly experiences the energy release and dissipation after the peak stress. It is found that when the unloading confining pressure rate is high, the duration of unloading confining pressure is short, the internal cracks of coal sample extend and circumferentially deform insufficiently, and the powers for energy dissipation and overcoming confining pressures are small. Moreover, most of the energy release when the coal sample ruptures, which make the coal sample damage seriously. Meanwhile, when the unloading confining pressure rate is larger, the damage rate of the coal sample increases faster before and after the rupture, which results in the sharp increase of the damage curve. Therefore, when the high-stress coal is excavated with a high construction speed, it is easy to cause a sudden release of a large amount of accumulated energy, causing serious disasters.