渗流-应力耦合作用下岩石三维充填裂隙的扩展机理研究

It is a common phenomenon that the fractures of natural rock mass are filled with medium and water. The filled medium has an important effect on the fracture propagation and seepage flow, and the fracture propagation will be dramatically accelerated by the fracture water, furthermore, the propagation and seepage of fractures promote each other. At present, the research of fracture propagation influenced by the filled medium pays more attention to the friction effect of crack faces, and the test, theory and simulation of fracture propagation under coupled seepage-stress fields need to be improved. Through the combination of laboratory experiment, theory analysis and numerical calculation, the project studies the propagation mechanism of the 3-D filled fractures in real rock under coupled seepage-stress fields. The specimens that are used in the experiment of complete stress-strain process seepage are made by cutting and bonding technology from real rock. From the tests, the initiation condition, propagation mode, coalescence of rock bridge and relevant mechanical mechanism of 3-D surface and internal fractures are studied with the help of CT real-time scanning technology. Considering a variety of damage mechanism, 3-D fractures interaction, and reflecting filled medium effectively, the fracture-damage model and the damage evolution equations of fracture rock mass are established under coupled seepage-stress fields. Then numerical method is used to simulate the dynamic propagation process of 3-D fracture propagation, coalescence of rock bridge etc al. Based on the above, the potential mechanism of different cracks propagation phenomenon is revealed.

天然岩体中的裂隙被介质充填和含水是一种较为普遍的现象，充填物对裂隙的扩展和渗流有重要的影响，裂隙水的存在会大大加速裂隙的扩展，而且裂隙的扩展和渗流相互促进。目前，充填物对裂隙扩展的影响研究多关注裂隙面之间的摩擦效应，渗流-应力耦合作用下裂隙扩展的试验、理论、模拟有待进一步完善。本项目采用室内试验、理论分析和数值计算相结合的方法，系统研究岩石三维充填裂隙在渗流-应力耦合作用下的扩展机理。利用真实岩石通过切割、粘结技术制作含三维裂隙的试件，借助CT实时扫描技术，进行全应力-应变过程渗流试验，研究岩石三维表面和内置充填裂隙在渗流-应力耦合作用下的起裂条件、扩展模式、岩桥贯通及其相应的力学机制；考虑多种损伤机制，建立渗流-应力耦合作用下可考虑三维裂隙相互作用及有效反映充填介质的裂隙岩体断裂损伤模型和损伤演化方程；通过数值计算模拟三维裂隙扩展、岩桥贯通等动态演化过程，揭示裂隙不同扩展现象的潜在机制。

本项目采用室内试验、理论分析和数值计算相结合的方法，系统研究了渗流-应力耦合作用下岩石三维表面、内置、通透裂隙的起裂、扩展以及岩桥贯通过程，得到了不同裂隙的不同扩展模式，获得了渗流、充填作用对裂隙扩展与岩桥贯通模式的影响规律，取得了裂隙的起裂强度、扩展角度、最终长度和含不同裂隙试件的破坏强度等一系列重要参数。渗透水压影响方面，恒定围压10MPa、渗透水压由2↗8MPa时，不同裂隙均以翼裂纹率先扩展，相较于无水压状态，起裂强度的削弱幅度由8.2%～16.3%，起裂角度由17°～28°，翼裂纹最终扩展长度为预制裂隙长度的0.8～1.4倍，试件破坏强度的削弱幅度由8.6%～19.3%；而反翼裂纹扩展与岩桥贯通模式受渗透水压影响不明显。充填物影响方面，恒定围压与渗透水压时，相较于无充填情况，充填裂隙的翼裂纹起裂强度提升了9.6%～12.9%，起裂角变化不明显，但扩展长度增长了近一倍；充填物对反翼裂纹长度的影响不大，对起裂角的提升范围为4°～11°，对试件破坏强度的提升范围为3.3%～7.1%。此外，除翼裂纹和反翼裂纹的扩展之外，充填裂隙的扩展还出现了与预制裂隙面交叉的剪切裂纹；充填物对岩桥贯通模式的影响主要体现在，非充填裂隙岩桥部位的扩展以翼裂纹与反裂纹的连通为主，而充填裂隙在岩桥部位则出现了明显的压剪破裂区。以双重介质理论和流固耦合理论为基础，充分考虑裂隙岩体的初始损伤、裂隙扩展等损伤机制，结合渗透系数演化方程，推导了渗流-应力耦合作用下裂隙岩体的损伤演化柔度张量，并建立了渗流-损伤耦合模型。将本构模型程序化后嵌入FLAC3D软件，模拟了裂隙在渗流-应力耦合作用下的扩展机理。数值模拟结果显示，渗流-应力耦合状态下裂隙的起裂以翼裂纹开始且时间较早，起裂处位于明显的拉剪应力集中区；而反翼裂纹的扩展则由压剪应力导致，扩展期约为抗压强度的80%，扩展长度也明显超过翼裂纹，随着试件的破坏而结束扩展。数值模拟再现了裂隙扩展的过程，裂隙扩展形态与试验结果取得了较高的吻合度。