【摘要】 通过开展灰岩巴西劈裂和单轴压缩声发射试验,探讨两种加载方式下岩石破裂声发射b值特性及b值计算影响因素。结果表明,累积计算b值拟合度高,误差较小;步距为5 dB时不同门槛值下b值随时间变化的总体规律基本一致,选择5 dB的步距和40 dB的门槛值计算b值比较合理,能够降低非岩石破裂信号对b值变化的影响。由动态b值的波动程度可以看出,在劈裂荷载下灰岩损伤演化过程可分为3个阶段,即(0～40%)δ_c(δ_c为峰值强度)、(40%～90%)δ_c和(90%～100%)δ_c,而在单轴加载下可分为:(0～80%)δ_c和(80%～100%)δ_c两个阶段,且不同阶段岩石内部损伤的程度不同。在裂纹扩展阶段,相比单轴加载,劈裂荷载下动态b值增加较为稳定,但在整个破坏过程中劈裂荷载下动态b值波动更大,在单轴压缩和劈裂加载方式下b值的大小取决于灰岩破裂面上的结构性质及破裂模式。更多还原

【Abstract】 Through the acoustic emission monitoring on two loading modes i.e. Brazilian splitting and uniaxial compression of limestone, the b-value characteristics of rock rupture and the impact factors are discussed. The results show that cumulative calculation of b-value has a high fitting degree and small error. When the step length is 5 dB, the overall change trend of b-value with time under different threshold values is similar. It shows that the calculation of b-value is more reasonable with the step length of 5 dB and threshold value of 40 dB, which can reduce the influence of non-rock fracture signals on the variation of b-value. Additionally,based on the fluctuation characteristics of the dynamic b-value, it can be seen that under the splitting load, the damage evolution of limestone can be divided into three stages:(0-40%)δ_c,(40%-90%)δ_c, and(90%-100%)δ_c. Under uniaxial compression load, the damage evolution of limestone can be divided into two stages:(0-80%)δ_c and(80%-100%)δ_c(δ_cis the peak strength). At different stages of rock damage, it presents different levels of damage in the rocks. In the crack propagation stage, compared with uniaxial compression load, the dynamic b-value increases steadily during crack growth process under Brazilian splitting load condition, and the dynamic b-value fluctuates greatly during the whole failure process. Through the experiments in this paper, it shows that the variation of b-value depends on the structural property and failure modes of the limestone fracture surface.更多还原