围压作用下不同裂隙位置复合岩裂纹演化研究

Study on the fracture evolution of composite rocks with different fracture locations under the action of surrounding pressure

【目的】为了揭示围压作用下预制单裂隙位置的改变对缺陷复合岩样特征应力以及裂纹扩展规律的影响,【方法】采用PFC2D软件并结合室内相似岩样试验进行分析,通过室内试验结果标定细观参数从而建立离散元模型,并对离散元模型进行三轴压缩试验分析单裂隙缺陷复合岩的裂纹演化规律。【结果】结果显示:围压的增加会使岩样的各项特征应力均有所增长。岩样峰值应力和损伤应力随围压增加呈线性关系,起裂应力随围压增加呈现出先突增后变缓的增长趋势。裂隙位置的改变对岩样特征应力的削弱程度明显不同。当位于结构面时,对起裂应力和损伤应力的削弱程度最高;当位于大理岩中时,对峰值应力的削弱程度最高。裂隙位置也对岩样内裂纹的萌生、扩展与贯通方式产生明显差异。当位于砂岩和结构面时,裂隙尖端产生的剪切裂纹向主应力方向扩展直至贯通导致岩样破坏;当位于大理岩时,裂隙尖端向主应力方向扩展的剪切裂纹以及砂岩部分产生的剪切裂纹聚集带两条主裂纹导致岩样破坏。【结论】结果表明:采用“试错法”标定建立PFC2D离散元模型模拟岩样三轴压缩试验,所得到的岩样裂纹演化规律与实际试验一致,对实际工程具有指导意义。

[Objective]In order to reveal the influence of the change of the prefabricated single crack position under the confining pressure on the characteristic stress and crack propagation law of the composite rock sample with defects,[Methods]in this paper,PFC2D software and indoor similar rock sample tests are used to analyze,and the mesoscopic parameters are calibrated through the indoor test result to establish a discrete element model,and the discrete element model is subjected to triaxial com-pression test to analyze the crack evolution law of single crack defect composite rock.[Results]The research shows that the char-acteristic stresses of rock samples increase with the increase of confining pressure.The peak stress and damage stress of rock samples show a linear relationship with the increase of confining pressure,and the cracking stress shows a sudden increase and then a slow growth trend with the increase of confining pressure.The weakening degree of characteristic stress of rock sample is obviously different with the change of fracture position.When it is located at the structural plane,the cracking stress and damage stress are weakened the most.When it is located in marble,the weakening degree of peak stress is the highest.The crack loca-tion also has obvious differences on the initiation,propagation and penetration of cracks in rock samples.When it is located in sandstone and structural plane,the crack propagation is caused by the shear crack generated at the crack tip extending to the direction of main stress until the rock sample is damaged.When it is located in marble,the crack propagation is caused by two main cracks,the shear crack propagating from the crack tip to the direction of the main stress and the shear crack aggregation zone produced by the sandstone part.[Conclusion]The research shows that the PFC2D discrete element model calibrated by the“trial and error method”is used to simulate the triaxial compression test of rock samples,and its crack evolution law is consistent with the actual test,which can guide the actual engineering.