非均质岩石劈裂条件下临界能量分布及其断裂特征

Critical energy distribution and fracture characteristics of heterogeneous rock under splitting condition

  • 摘要: 为探明非均质岩石受载拉伸破裂的宏观物理力学特征,设计并开展了岩石单轴劈裂试验,通过采集岩石变形特征、声发射参数和表面温度场特征,分析、揭示非均质岩石劈裂过程中变形协调性与临界能量分布、断裂特征以及局部应力阶段下的临界特征。研究中通过定量计算获得了花岗岩的变形空间变异性特征,并针对不同变形协调性花岗岩在加载过程中的声发射bi值、临界能量分布以及RA(上升时间/幅值)−AF(平均频率)特征参数、破裂断面形貌进行了相关分析。试验结果表明:① 可采用岩石90%峰值应力水平的变形空间变异系数评价区分岩石变形协调的差异性,其与试样抗拉强度近似呈负相关关系;② 声发射bi值随加载过程呈现“波动—上升—跌落”变化趋势,不同变形协调性的试样在不同应力水平下的声发射事件占比规律不同,变形协调性越好,声发射事件增长规律越稳定;③ 不同变形协调性花岗岩劈裂破坏过程具有自组织临界特征,全过程和局部应力阶段下的花岗岩能量概率密度函数服从幂律分布,且随着变形协调性变差,加载后期局部应力阶段下的幂律分布曲线逐渐向全过程幂律曲线逼近;④ 不同变形协调性试样的RA − AF的变化规律相似,但变形协调性越差的试样在破裂时抗拉强度低、变形空间变异系数大,多发生小尺度张拉破裂,断面粗糙导致JRC大,所释放的能量也较小,更容易进入临界状态,而岩石变形协调性越好的试样的相应特征恰好相反。基于上述研究,可实时监测深部巷道围岩多点应变规律,将变形空间变异系数突增的点作为巷道张拉破裂的预警信息。

     

    Abstract: To explore the macroscopic physical and mechanical characteristics of the tensile fracturing of heterogeneous rocks under loading, uniaxial splitting tests were designed and carried out on rock samples. By collecting rock deformation characteristics, acoustic emission parameters, and surface temperature field characteristics, the study analyzed and revealed the deformation coordination, critical energy distribution, fracture characteristics, and critical characteristics under local stress stages in the rock splitting process. Through quantitative calculation, the study obtained the spatial variability characteristics of the deformation of granite. It also conducted relevant analyses on the acoustic emission bi value, critical energy distribution, RA (rise time/amplitude) - AF (average frequency) characteristic parameters, and fracture surface morphology of granites with different deformation coordination during the loading process. The experimental results show: ① The deformation space variability coefficient at the 90% peak stress level of the rock can be used to evaluate the differences in rock deformation coordination, and it is approximately negatively correlated with the tensile strength of the specimen; ② The acoustic emission bi value shows a “fluctuating-rising-falling” trend during the loading process. Samples with different deformation coordination have different proportions of acoustic emission events at different stress levels, and the more coordinated the deformation, the more stable the growth pattern of acoustic emission events; ③ The splitting and fracturing process of granites with different deformation coordination exhibits self-organized critical characteristics. The energy probability density functions of the entire process and the local stress stages follow power-law distributions, and as the deformation coordination deteriorates, the power-law distribution curve in the local stress stage at the later stage of loading gradually approaches the power-law curve of the entire process; ④ The change patterns of RA - AF values are similar for samples with different deformation coordination, but the samples with poorer deformation coordination have lower tensile strength, larger deformation space variability, more small-scale tensile fractures, rougher fracture surfaces with larger JRC, smaller released energy, and are more likely to enter a critical state, while the opposite is true for rocks with better deformation coordination. Based on the above research, it is shown that the multi-point strain pattern of the surrounding rock of the deep tunnel can be monitored in real time, and the points with a sudden increase in the coefficient of variation of the deformation space can be used as the early warning information for the tensioning and rupture of the tunnel.

     

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