季冻区边坡裂隙岩体破裂机理试验及数值流形方法研究

The failure of fractured rock slope triggered by freezing-thawing process in western seasonal frozen area is one of the fundamental subjects of rock mechanics, which possesses essential theoretical and practical value to develop the failure mechanism study of fractured rocks under freeze-thaw cycles. The combination of laboratory test, theoretical analysis and numerical simulation methods are synthesized adopted. In the project, the failure mechanism of fractured rock under freeze-thaw cycles through experimental and numerical manifold methods are implemented respectively. According to the triaxial compression acoustic emission tests, the whole failure characteristics of rock-like materials are achieved, which assist in building the quantitative relationships between initial cracks and mechanical parameters. Easily measured and calculated multi-parameter joint control variables are proposed. Strength degradation constitutive models are explored. Ultimately, the strength degradation mechanism is revealed. Based on three-dimensional acoustic emission tests, the intersecting criterions between initial and subsequent cracks are analyzed. A new crack propagation algorithm and corresponding numerical manifold element program are presented. Based on the program, the primitive simulation calculation models in terms of sample size are conducted, which simulate the size effect of the failure mechanism of fractured rocks. On account of the mechanical significance of the representative element volume of fractured rocks, the manifold element program of fractured rock slope is obtained, which may provide relevant basis for further engineering application in seasonal frozen area.

西部季节性冻土地区基于冻融作用诱发的裂隙岩体边坡破裂规律研究是寒区岩体力学的基础性课题之一。开展冻融作用下裂隙岩体扩展断裂机理研究具有重要的理论价值和工程实践意义。课题采用试验、理论和数值模拟相结合的手段开展冻融作用下裂隙岩体扩展断裂机理试验及裂隙岩体断裂过程数值流形方法研究。基于三轴压缩裂隙岩样破坏全过程声发射试验，构建裂隙岩体初始缺陷与宏观力学参数间的定量关系，提出易测量和计算的多参数联合控制变量，建立强度劣化本构模型，揭示岩体次生裂隙扩展的差异性强度劣化规律；基于裂隙岩样破坏全过程三维声发射定位信息研究冻荷次生裂隙与初始裂隙相交准则，给出裂隙分叉扩展算法并开发数值流形元程序。基于编制的流形元程序以试验试样尺寸为基元模拟裂隙岩体破裂机理计算模型的尺寸效应，确定单元表征体特性，提出可用于模拟裂隙岩体边坡破坏规律分析及破裂全过程的数值流形方法，可为季冻区裂隙岩体边坡工程灾害防治提供支撑。

岩体在季节性冻融循环作用下的损伤劣化会引发严重的工程地质问题。岩体的冻融循环损伤主要表现为水冰相变和载荷驱动下原生裂隙的扩展。由于在季节性冻融山区裂隙周期冻结为其常态，加之裂隙的扩展发育具有时间依赖性，因此有必要研究周期冻融循环条件下含水和含冰裂隙的扩展机制。本项目采用理论分析和室内测试相结合的方法和思路，首先分析裂隙中水和冰的变化过程；之后探讨不同阶段裂隙的扩展和演化及其作用下裂隙的力学响应；结合对不同阶段不同饱和度砂岩的损伤演化规律的测定；最终结合三维可视化软件及分形理论，对冻融过程中宏观力学指标的演化过程进行定量分析，建立考虑饱和度和裂纹几何特征的裂隙发育判据，并通过冻融周期条件下裂隙扩展的实验对理论分析进行检验。研究发现：①裂隙在温度的变化过程中稍滞后于环境温度的变化，在冻结和融化阶段有显著的物理变化，即裂纹体积、裂纹表面积和裂纹比表面积，在冻融循环过程中，裂纹体积、裂纹表面积表现出上升的趋势。②冻融循环过程中饱和完整试样连通孔隙比率曲线波动幅度相对稳定，对于预制裂纹试样，端部破碎程度远远高于内部区域，预制裂隙是从预制裂隙附近增长，并逐渐扩展到岩桥区域。③随着饱和度增大，压密和塑性变形阶段突出，弹性阶段持续时间减小；峰值强度和弹性模量随饱和度增大呈“下凸式”指数降低，而随冻融循环次数增加呈“下凹式”指数减小。④将不同饱和度岩样冻融后的损伤状态作为第1种损伤状态，荷载作用下引起的损伤作为第2种损伤状态，可得到不同饱和度岩样在两种损伤状态下的一维本构关系。⑤冻融循环作用下完整饱和试样的总体孔喉结构基本一致，大孔主要在试样外围分布，针对预制裂纹试样则主要集中在裂纹处，饱冰试样的孔喉结构发育更密集。项目实施对于指导应对寒区工程活动所面临的岩体冻融损伤灾害具有重要意义。