岩石裂纹扩展诱发的强度弱化模型研究

岩石应力应变本构关系对于判断岩石强度、变形力学特性有着重要的意义,细观裂纹对岩石力学特性又有着重要的影响。基于细观裂纹扩展模型,将裂纹角度影响引入模型,并结合宏细观损伤定义联系,建立了一个考虑裂纹角度影响的轴向应力应变本构模型,并解释了围压与轴向应变本构关系,分析了裂纹贯通与岩石失效极限应变之间的联系,然后将该本构模型,与常规压缩试验与循环加卸载试验对比分析得到的试验规律相结合,提出了一个岩石内部裂纹扩展、变形损伤作用下岩石压缩强度弱化模型。并通过将不同围压下的裂纹启裂应力试验值和理论公式相结合,预测了模型中难以试验直接获取的关键参数μ,a,β,φ。其中初始裂纹尺寸a与裂纹角度φ,是由真实岩石中随机分布裂纹尺寸、角度平均化思维获取。随着裂纹扩展或应变增加,岩石压缩强度开始保持不变,当岩石达到一定损伤后不断降低。该强度弱化模型的应用,为地下工程围岩稳定性评价提供了一个重要的理论支持。

Study on Strength Weakening Model Induced by Microcrack Growth in Rocks

The stress-strain relation has a great significance for the mechanical properties of strength and deformation of rocks. Microcrack growth plays an important role in the mechanical properties of rocks. In this study, based on the wing crack growth model introducing crack angle effect, and coupling the micro-macro definition of damage, an axial stress-strain relation considering crack angle effect was established and the relation between confining pressure and axial strain was also illustrated. The relationship between crack coalescence and failure limit strain was analyzed. And then, coupling this established stress-strain relation, and an obtained law by comparing the results from the conventional compressive test and the cyclic loading and unloading test, a strength weakening model caused by microcrack growth, deformation and damage was proposed. Combining the theoretical and experimental relations between crack initiation stress and confining pressure, the key parameters μ, a, β and φ were predicted. An average idea was used to achieve the model parameters of initial crack size a and crack angle φ. The rock compressive strength keeps constant firstly, and then decreases with wing crack growth or the increasing axial strain. This strength weakening model provides an important theoretical help for evaluating the stability of surrounding rock in underground engineering.