硬岩裂纹起裂强度和损伤强度取值方法探讨

岩石裂纹起裂强度σci和损伤强度σcd的研究对探讨岩石渐进破坏过程和脆性破坏机制,建立岩石的起裂强度和长期强度准则具有重要意义。鉴于此,系统总结了岩石起裂强度和损伤强度的4种计算方法,包括裂纹应变模型计算法,声发射参数取值法,侧向应变、体积应变曲线观察法和移动点回归法,并以大理岩和花岗岩在单轴压缩条件下为例,详细描述了用不同方法计算σci和σcd时存在的问题。研究结果表明,裂纹应变模型法物理意义明确,可以方便和准确地确定岩石的σci和σcd;声发射撞击率可以定性或半定量了解岩石的渐进破坏和损伤过程,但无法准确定量确定σci和σcd;移动点回归法计算体积应变刚度时受取值点间隔影响较大,而且加载过程中不同阶段的特征并不明显,难以确定起裂强度值。研究结论可为加深对岩石裂纹起裂强度和损伤强度的重要意义的认识,了解两个强度值的计算方法并合理选取其计算方法提供有益的参考。

Discussion on methods for calculating crack initiation strength and crack damage strength for hard rock

Strength thresholds of crack initiation ( ) and crack damage ( ) of hard rock are of great significance not only for understanding the progressive failure process and brittle failure mechanism but also for establishing the crack initiation strength criterion and long-term strength criterion. In view of this, four methods to calculate the crack initiation and damage strength, including crack volumetric strain model, acoustic emission method, lateral strain and volumetric strain observation method, moving point regression technique, are summarized systematically; and marble and granite in uniaxial stress state are taken as examples to show problems in determining and by each method. Results show that and can be obtained conveniently and precisely through crack volumetric strain model which has a clear physical meaning; progressive failure and damage process of rock can be comprehended qualitatively or semi-quantitatively by analysis of acoustic emission hit rate; but and can not be acquired accurately. Curve of volumetric strain stiffness is strongly influenced by data intervals and characteristics of different stages during loading are not obvious when moving point regression technique is used, which makes the determination of difficult. The result could contribute to understanding the importance and calculating methods of crack initiation and damage strength thresholds and provide a useful reference to choose appropriate calculating method.