基于裂隙时效演化的软岩路堑边坡蠕变-失稳机理研究

The process of fracture propagation, modulus attenuation and strength deterioration of soft rock caused by long-term external forces is obviously time-dependent, which makes such slopes very easy to be creep-failure, causing property losses and casualties. Creep-failure mechanism and long-term stability prediction method of soft rock cutting slope based on fracture aging evolution deserve further study. Based on the study of creep properties of undisturbed soft rock, this project designs soft rock-like specimens which can reproduce creep properties and develops prefabricated fracture skill. Reveals the aging evolution law and micro-mechanism of soft rock cracks by using CT scanning, SEM and numerical image processing technology. Constructs creep damage constitutive model of soft rock considering aging evolution of cracks. Develops the constitutive model above-mentioned by using finite difference and discrete element technology. Based on the model, the creep- failure numerical calculation of the soft rock cutting slope is carried out by combining the initial crack generation algorithm, and the long-term evolution laws of the fracture, stress, strain field and plastic zone are obtained. Large-scale centrifugal model tests are carried out to obtain the typical failure modes of the prefabricated fractured soft rock cutting slope. The index, criteria and long-term stability prediction method of soft rock cutting slope creep-failure will be put forward. The research results will further improve and develop the creep-failure theory of soft rock, as well as have important theoretical and practical significance for the long-term stability prediction of soft rock cutting slope.

外力长期作用引发的软岩裂隙扩展、模量衰减以及强度劣化过程均具有非常明显的时效特征，致使此类边坡极易出现蠕变-失稳现象，造成重大财产损失与人员伤亡。基于裂隙时效演化的软岩路堑边坡蠕变-失稳机理与长期稳定性预测方法值得深入探讨。本研究以原状软岩蠕变特性为基础，设计可再现蠕变特性的类软岩试样并研发预制裂隙技术；利用CT扫描、SEM以及数值图像处理技术揭示软岩裂隙时效演化规律与细观机理；构建考虑裂隙时效演化的软岩蠕变损伤本构模型；运用有限差分和离散元技术开发上述本构模型，结合初始裂隙生成算法开展软岩路堑边坡蠕变-失稳数值计算，得到裂隙、应力、应变场以及塑性区等的长期演化规律；开展大型离心模型试验，得到预制裂隙软岩路堑边坡典型破坏模式，提出软岩边坡蠕变-失稳判定指标、标准与长期稳定性预测方法。研究成果将进一步完善和发展软岩蠕变-破坏理论，对软岩路堑边坡的长期稳定性预测具有重要的理论与实践意义。

在软岩路堑开挖过程中以及开挖完成后，原状岩体仍会保持较高强度，较少立即发生破坏。但在公路长期运营过程中，受软岩裂隙时变性的影响，岩体模量与强度逐渐降低，边坡产生蠕变变形，抵抗滑动能力减弱，最终引起边坡失稳。. 本项目已经完成软岩相似材料研究，制作出了适用于模拟粉砂质泥岩的相似材料配比与制作方法。利用多功能三轴试验设备开展了常规三轴试验、三轴卸荷试验以及三轴蠕变实验，分析了不同加载方式下粉砂质泥岩裂隙演化规律。构建了粉砂质泥岩蠕变变形本构模型，利用Fish语言编写程序，对FLAC3D6.0软件进行二次开发，得到了数值模拟结果。利用扫描电镜观察粉砂质泥岩在不同应力条件下破坏后的断面细观特点，揭示了不同应力条件下粉砂质泥岩的破坏机理。除此之外，本项目还研究了冻融循环以及酸环境下粉砂质泥岩的强度劣化机理。. 主要结论如下：可采用水、重晶石粉、石膏质量、黏土矿物在一定配比下制备粉砂质泥岩相似材料。可通过调整粘土矿物比例并增加纳米材料从而改善材料的膨胀性、单轴强度等关键指标。在同一围压下，试样的蠕变随着加载等级的提高，在不同应力水平下表现出明显的减速蠕变阶段、稳态蠕变阶段和加速蠕变阶段。通过统一流变力学模型理论确定粉砂质泥岩蠕变模型结构为H-H|N-N|V，根据叠加原理得到了新建MKNVPB模型的一维应力状态下的蠕变本构方程。冻融循环作用下粉砂质泥岩力学性能劣化机理为岩样内部孔隙中水-冰相交替作用使得岩体内部孔隙数目增加且孔径增大，部分微孔联通转化为中孔，使得中孔孔隙率迅速增加，导致岩体单轴抗压强度与弹性模量减小，破坏形式由脆性向塑性转变。. 本项目所得成果对软岩路堑边坡的设计、施工、防护以及失稳预警具有指导意义。本研究所用方法对进一步探究多因素影响下各类岩石的蠕变-破坏机理以及各类岩质边坡的长期稳定状态具有十分重要的参考价值。