裂隙砂岩渐进破坏特征及损伤本构模型

Progressive Failure Characteristics and Damage Constitutive Model of Fractured Sandstone

摘要

为全面探讨裂隙特征对岩体强度及变形破坏的影响,本文利用离散元软件PFC^3D对裂隙砂岩展开不同围压、不同预裂隙倾角的变形破坏试验.结合变形破坏全过程的宏观力学特性,基于细观裂纹数目演化规律,分析裂隙砂岩的渐进破坏特征;进而根据细观裂纹数目定义损伤变量D,构建能够反映裂隙岩体渐近破坏的损伤本构关系.结果表明:裂隙砂岩具有明显的围压效应,围压越大,抗压强度越大;相同围压下,裂隙砂岩抗压强度随预裂隙倾角增大呈现先减小后增大的趋势.裂隙砂岩变形破坏过程对应细观裂纹数目演化曲线具有阶段性,依据裂纹数曲线进行了平滑段、线性增长段、上凹增长段及最后趋于平缓段的阶段划分,确定了相应的特征应力点.渐进破坏过程中,0°、90°裂隙岩样细观裂纹几乎遍布在整个试样中,30°、45°及60°裂隙岩样细观裂纹趋于沿预裂隙与上下加载面贯通面产生.各特征应力点处,总裂纹数随围压增大而增大,且围压越大剪切裂纹比例越大,总裂纹数随预裂隙倾角增大先减小后增大.根据细观裂纹数构建的本构关系具有合理性,能够较好地反映裂隙砂岩的基本力学特征.

Abstract

To comprehensively investigate the influence of fracture characteristics on rock mass strength and deformation failure, this study employs the discrete element method software PFC ^3D to conduct deformation and failure tests on fractured sandstone under varying confining pressures and fracture inclinations. By integrating the macroscopic mechanical properties throughout the entire deformation and failure process and analyzing the progressive failure characteristics based on the evolution of the number of microcracks, a damage variable D is defined according to the number of microcracks, and a damage constitutive relationship is established that can reflect the asymptotic failure of fractured rock masses. The results indicate that: The fractured sandstone has obvious confining pressure effect, the larger the confining pressure, the larger the compressive strength; Under the same confining pressure, the compressive strength of fractured sandstone shows the trend of decreasing and then increasing with the increase of fracture inclination angle. The deformation and damage process of fractured sandstone corresponds to the evolution curve of the number of microscopic cracks with a stage, based on the curve of the number of cracks, a smooth section, a linear growth section, an upward concave growth section and the last tends to be flat section of the stage division, to determine the corresponding characteristics of the stress point. During the progressive damage process, the microcracks of 0° and 90° fractured rock samples were almost spread throughout the whole sample, and the microcracks of 30°, 45° and 60° fractured rock samples tended to be generated along the pre-fractured and the upper and lower loading surfaces. At each characteristic stress point, the total number of cracks increases with the increase of confining pressure, and the larger the confining pressure, the larger the proportion of shear cracks, and the total number of cracks decreases and then increases with the increase of the inclination angle of the pre-fracture. The constitutive relationship established based on the number of microcracks is reasonable and can well reflect the basic mechanical characteristics of fractured sandstone.

关键词

裂隙砂岩 / 裂纹数目 / 渐进破坏 / 损伤本构模型 / PFC ^3D / 围压 / 预裂隙倾角

Key words

fractured sandstone / crack number / progressive failure / damage constitutive model / PFC ^3D / confining pressures / fracture inclinations

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基金资助

四川省自然科学基金项目(2022NSFSC0279)

四川省自然科学基金项目(2022NSFSC1009)