深部岩石蠕变-疲劳交互作用下的时滞性破坏机制与损伤模型

A large number of disasters in deep rock mass induced by engineering disturbances show that, the influence of creep-fatigue interaction on the time-lag failure mechanical behavior of deep rock is significant. In classical rock mechanics theory, this influence cannot be evaluated quatitatively, which is the major problem restricting the prediction and prevention of time-lag failure disaster in deep rock engineering. In this project, triaxial test and AE test under the creep, fatigue, and creep-fatigue interaction conditions will be carried out under the help of a self-developed creep-fatigue linkage triaxial testing system. The deformation, the precursor of time-lag failure, and the lagged time of rock under the three kinds of loading will be studied. The mesocopic damage structure evolution characteristics will be studied using mesoscopic numerical simulation, NMR test, and fracture fluorescence observation, and a general damage evaluation method based AE signal will be established. The sensitivity of stress level and holding time of creep loading, upper and lower stress, frequency of fatigue loading, and the order of loadings to the damage variable will be clearly defined. Then, the mesoscopic damage mechanism of time-lag failure under creep-fatigue interaction condition will be revealed. At last, based on establishing the coupling control equations of damage control factors with damage variables, and the determination method of interaction coefficients in the two kinds of damage nonlinear superposition hypothesis, a nonlinear damage constitutive model and life prediction model of rock under creep-fatigue interaction condition will be established. This study is closer to the real working condition of deep rock mass, which can provide a new theory for the control of surround rock of deep engineering construction and the prevention of time-lag failure disaster.

大量的工程扰动诱发深部岩体重大灾害案例表明，蠕变—疲劳交互作用对围岩时滞性破坏行为影响巨大，经典岩石力学无法对此进行量化评价，是制约深部岩石工程时滞性灾害预报和防控水平的瓶颈之一。项目拟借助自行研制的蠕变—疲劳联动三轴试验机，开展岩石蠕变、疲劳及蠕变—疲劳交互三轴试验和AE监测，研究三类荷载作用下岩石变形、时滞性破裂前兆和滞后时间的表观规律。综合离散元数值仿真、NMR测试和裂隙荧光观测等手段，建立通用损伤变量的AE表征方法，明确蠕变应力水平、持时，疲劳上下限应力、频率，及次序等因素对损伤变量的敏感性，阐释蠕变—疲劳交互作用下岩石时滞性破裂的细观力学机制。通过建立致损主控因素与损伤变量的耦合关系式，及损伤非线性叠加假说中的叠加模式和交互系数求参方法，最终构建蠕变—疲劳作用下岩石非线性损伤本构和寿命预测模型。本研究更加贴合深部岩体的实际工况，可为深部工程围岩变形控制和时滞性灾害防治提供新理论。

深部岩石工程在施工与运营期间，除了受到开挖应力调整，还会间断性的受到诸如地震波、交通荷载甚至爆破冲击波等循环荷载作用，影响深部岩石工程安全。为探究深部岩石在蠕变与疲劳交互作用下力学性能，开展不同围压、不同应力水平蠕变和不同疲劳幅值的蠕变与疲劳交互试验并同步进行声发射测试，进而建立蠕变与疲劳交互作用下本构模型，并验证模型适用性。结论如下：.1 单轴蠕变疲劳交互力学试验.1）蠕变与疲劳交互作用会显著降低岩石寿命，各级蠕变与疲劳引起的应变增量和蠕变速率整体呈现出“V”型变化规律；2)各级疲劳后的蠕变速率不小于疲劳前蠕变速率，表明低幅疲劳对岩石蠕变会有一定促进作用；3）声发射振铃数主要集中在疲劳加载段，全过程中呈现簇状分布，疲劳荷载幅值越大，声发射事件越剧烈。声发射破裂点与核磁扫描结果均表明裂隙演化规律为在平面上由内向外发展，在高度上由中部向两端延伸；4）岩石以剪切破坏为主，且疲劳幅值越小，破坏时岩石粉末越多。.2 三轴蠕变疲劳交互力学试验.1）各围压下偏应力-轴向应变均形成明显滞回圈，随着疲劳次数增加，滞回圈呈现由疏到密的特征，围压越大，由疏到密的现象越明显。不同围压下的偏应力-径向应变存在的差异十分明显；2）四种围压下，岩石蠕变疲劳交互次数表现出随着围压增大，交互次数增多的规律。首次疲劳轴向应变速率随着围压增大而减小，各工况轴向应变增量则整体表现为负指数的非线性衰减规律；3）声发射测试结果表明疲劳段声发射信号则密集出现且数值要显著大于蠕变段结果，声发射随时间均呈现“簇状”分布特征。声发射与核磁测试结果共同表明，破裂点在试样高度方向上由中部向两端延伸，在平面方向上则是由试样核心区域向外侧发展；4）蠕变疲劳交互过程中，随着围压增大，试样破坏由劈裂剪切共存逐步向单一剪切，最终形成“X”型的共轭破坏特征。.3 蠕变疲劳交互本构模型研究.1）考虑蠕变疲劳交互过程中荷载特征以及岩石变形特性，考虑疲劳过程的蠕变行为，针对有效疲劳部分进行傅里叶变换，随后利用积分的思想推导出疲劳塑性应变的力学表达式；2）以45-4MPa工况为基准，求出首次蠕变与疲劳段的模型参数，随后按应变增量比例对其他工况下模型参数进行调整确定；3）通过与试验数据对比，试验值与理论值匹配度较高，验证模型的准确性与适应性。