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采用岩石三轴试验机和声发射监测系统,研究我国高放废物地质处置库北山预选区深部花岗岩在单轴和三轴压缩条件下的破裂过程和强度特性。基于试验结果,分析岩石应力–应变曲线及其与声发射事件的时空分布关系,揭示岩石在压缩变形各个阶段的破裂演化机制,探讨3个特征应力水平(裂隙初始强度(ci)、裂隙损伤强度(cd)和峰值强度(c))对围压的依赖性。研究表明:(1)在低围压(0~2 MPa)条件下,大量分散或沿轴向应力方向分布的声发射事件与岩石宏观上的高密度竖向破裂相对应,从而导致岩石黏结力弱化,随着围压的增加,岩石逐渐从劈裂破坏向剪切破坏模式过渡,且裂隙增量最大值发生在应变软化阶段,其与岩石扩容率的变化规律一致;(2)采用提出的累计声发射撞击数方法结合应力–应变测量,可准确识别ci,与cd相比,ci对围压的依赖性较不敏感,该行为在低围压条件下更为突出;(3)单一的Hoek-Brown强度准则不足以充分描述岩石在劈裂和剪切并存条件下的峰值强度变化规律,赋予2个材料参数mi值的分段式Hoek-Brown强度曲线应更为合理。
A rock triaxial testing machine and acoustic emission monitoring system were used to study the rupture process and strength characteristics of deep granite in North Beishan Preselected Area of China’s high-level radioactive waste disposal plant under uniaxial and triaxial compression conditions. Based on the experimental results, the relationship between rock stress-strain curve and space-time distribution of acoustic emission events is analyzed. The mechanism of rock fracture evolution at various stages of compression deformation is revealed. Three characteristic stress levels (initial fracture strength (ci), fracture damage strength (cd) and peak intensity (c)) on confining pressure. The results show that: (1) Under the low confining pressure (0 ~ 2 MPa), the acoustic emission events distributed in a large amount or along the axial stress direction correspond to the macroscopic high-density vertical rupture, which leads to the rock adhesion With the increase of confining pressure, the rock gradually transitions from cleavage failure to shear failure mode, and the maximum of crevice crevice occurs in the stage of strain softening, which is consistent with the law of rock expansion rate. (2) Cumulative cumulative number of acoustic emission shocks combined with stress-strain measurements can accurately identify ci, compared with cd, ci is less sensitive to confining pressure, which is more prominent under low confining pressure conditions; (3) Single The Hoek-Brown strength criterion is not enough to fully describe the variation of peak strength under the coexistence of splitting and shearing. The Hoek-Brown strength curve of two sections is more reasonable.