开放型岩桥裂纹贯通机理及脆性破坏特征研究

Crack coalescence and brittle failure characteristics of open rock bridges

端部开裂的裂隙岩体内部岩桥贯通是导致岩体突发失稳破坏的主要原因,脆性破坏特征明显。利用声发射仪和岩石力学刚性试验机,对不同长度开放岩桥开展单轴压缩试验,结合高速摄像机记录信息,分析了开放岩桥裂纹起裂、扩展、贯通规律及脆性破坏过程力学特性和声发射特征,并通过三维断裂力学理论揭示了开放岩桥裂纹起裂扩展贯通机理。研究结果表明:与闭合裂纹相比,开放裂纹岩桥主裂纹从下部预制裂纹内尖端起裂,往上部拐折扩展贯通岩桥和上端面,贯通过程岩桥发生逐次多级破坏,次裂纹主要沿主裂纹拐折处起裂扩展贯通岩桥及下端面;应力曲线表现出峰前"波动上升"和峰后"滞留–突降"特征,声发射参数"多峰值"现象明显,阶段性和突发性特征突出;同时,三维理论分析表明裂纹起始扩展方向与岩桥长度无关,沿最大压应力方向扩展。研究所得开放岩桥裂纹扩展贯通特征可为裂隙岩体突发失稳破坏过程提供理论依据。

The coalescence of rock bridge of fractured rock mass with end cracking is the main cause of the sudden damage of the rock mass, and the brittle failure is obvious. The uniaxial compression tests are conducted on the open rock bridges with different lengths by using the acoustic emission tester and the rock mechanics rigidity tester. By use of the information recorded by high-speed camera, the crack coalescence laws and acoustic emission characteristics of open rock bridges are analyzed. The mechanism of crack initiation of open rock bridges is revealed by the theory of three-dimensional fracture mechanics. The results show that compared with the closed crack, the main crack of an open rock bridge starts from the tip of the crack at the lower part, and the main crack turns to the upper part expanding through the rock bridge and the top end. During the coalescence of the main crack, the rock bridge presents successive multi-stage failure. The secondary crack propagates along the inflection of the main crack and extends through the rock bridge and the lower end. The stress curve shows the "fluctuation rise" before the peak and "stagnation-sudden" after the peak, and the "multi-peak" phenomenon of the acoustic emission is obvious, with obvious stage and sudden features. Simultaneously, the three-dimensional theoretical analysis shows that the crack initiation direction is independent of the length of the rock bridge and extends along the direction of the maximum compressive stress. The obtained crack propagation characteristics of the open rock bridge may provide a theoretical basis for the sudden failure of the fractured rock mass.