深部椭圆形洞室围岩冲击岩爆实验研究

Experimental study on impact rockburst of surrounding rock in deep elliptical caverns

利用自主研发的冲击岩爆设备,室内再现真三轴条件下含椭圆形洞室的冲击岩爆现象,实验结合应力采集、录像及声发射等实时测试系统分析椭圆形洞室冲击岩爆的演化过程、破坏应力特征值、碎屑特征、爆坑特征、速度场特征以及声发射特征。结果表明:椭圆形洞室冲击岩爆过程可以分为4个阶段:平静期,小颗粒弹射,块体剥落以及岩爆;扰动荷载的作用使围岩切向应力值迅速增加超越单轴抗压强度,促使围岩体产生剧烈岩爆现象;岩爆实验碎屑主要以大于5 mm的碎屑为主,碎屑形态主要为薄板状分布,与现场岩爆碎屑分布特征类似;爆坑对称的分布于洞室的左右两侧壁,位置与扰动方向垂直,爆坑形态表现出V字型;速度场在块体剥落和岩爆阶段呈现出先增加再降低的特征,在岩爆发生时刻达到峰值;声发射计数率与加载方向个数密切相关,计数率和累计计数在岩爆时刻迅速增加。随着加载方向个数的减少,声发射主频带逐渐变窄,主频带主要分布在100~200 kHz范围,岩爆时刻出现了40~70 kHz低频带的信号,同时也存在高频和超高频信号,证实岩爆破坏的复杂性。

Using a self-developed impact rockburst equipment,the rockburst phenomena of surrounding sandstone of elliptical caverns under true triaxial loading were reproduced.The stress acquisition system,real-time video recording system and acoustic emission(AE)system were used to investigate the sandstone rockburst failure.Specifically,the failure characteristics such as stresses,fragments,rockburst pits,velocity field and AE were discussed in detail.The results show that the process of impact rockburst of surrounding sandstone of elliptical caverns can be divided into four stages,i.e.,quiet period,small particle ejection,spalling and rockburst.Additionally,the disturbance loading makes the tangential stress of the surrounding rock increase rapidly(beyond the uniaxial compression strength),which promotes the violent rockburst phenomenon.Furthermore,the lengths of most rockburst fragments are larger than 5 mm,and the dominant shape of the fragments is flake,which is similar to the distribution characteristics of rockburst fragments in field.Moreover,the V-shape pits are symmetrically distributed on the left and right side walls of the cavern,and their positions are perpendicular to the disturbance direction.The velocity field shows a trend of increasing and then decreasing during the both stages of spalling and rockburst,and the velocity reaches the peak at rockburst.Finally,the AE count rate is closely related to the number of loading directions,and the AE count rate and the cumulative count both increase rapidly at the rockburst stage.The main frequency band of AE gradually becomes narrow with decreasing the number of load directions,and the main frequency is mainly distributed between 100 to 200 kHz.The low-frequency(40–70 kHz),high-frequency and ultra-high-frequency AE signals all appear at the rockburst stage,confirming the complexity of rockburst.