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变上限循环加卸载裂隙砂岩宏细观损伤特征研究

Study on macro-and mesoscopic damage characteristics of fractured sandstoneunder cyclic loading and unloading with variable upper limit

  • 摘要: 为研究裂隙岩体在循环荷载作用下的宏细观损伤特征,以不同长度预制裂隙砂岩为研究对象,开展变上限循环加卸载试验,分析岩样的力学特性和宏观破坏特征;基于XRD分析结果构建裂隙砂岩UDEC数值模型,分析模型的细观损伤规律并揭示其机制。结果表明:加卸载作用能够强化裂隙较小岩样的抗变形能力,相反会增加裂隙较大岩样的破坏速度;随预制裂隙长度增大,岩样宏观破坏特征由拉剪复合破坏转化为以剪切破坏为主,且损伤的不可逆性逐渐提高;加卸载作用下岩样的损伤演化过程可划分为“弹性−强化−疲劳−破坏”4个阶段,弹性阶段模型未产生损伤,强化阶段模型形成有效抗力结构,疲劳阶段累积损伤大幅提高,卸载时张拉裂纹扩展;疲劳阶段加载过程裂纹相互扩展连结,相邻剪切微裂纹之间块体的接触点被破坏,块体间的连结失效,卸载过程应力下降模型松弛,块体间失效的连结在此时张开进而导致张拉裂纹在剪切微裂纹间萌生,加快模型的失稳破坏。研究结果揭示了变上限循环加卸载下裂隙砂岩的宏细观损伤特征,为科学评价工程稳定性提供参考。

     

    Abstract: Abstract: In order to study the macro and micro damage characteristics of fractured rock mass under cyclic load, cyclic loading and unloading tests with variable upper limit were carried out to analyze the mechanical properties and macro failure characteristics of the samples. Based on the results of XRD analysis, a UDEC numerical model of fractured sandstone is constructed to analyze the microscopic damage law of the model and reveal its mechanism. The results show that: loading and unloading can strengthen the deformation resistance of the samples with small cracks, and on the contrary increase the failure velocity of the samples with large cracks; With the increase of the prefabricated fracture length, the macroscopic failure characteristics of the sample changed from tensile shear failure to shear failure, and the irreversibility of the damage gradually increased. The damage evolution process of the sample under loading and unloading can be divided into four stages: “elasticity-strengthening-fatigue-failure”. No damage occurs in the elastic stage model, while an effective resistance structure is formed in the strengthening stage model. Cumulative damage increases significantly in the fatigue stage, and tensile cracks expand during unloading. During the loading stage, cracks expand and connect with each other, the contact point pole of the block between adjacent shear microcracks is destroyed, and the connection between the blocks fails. During the unloading process, the stress drop model is relaxed, and the failed connection between the blocks opens up at this time, leading to the initiation of tension cracks between the shear microcracks, and accelerating the instability and failure of the model. The research results reveal the macro and micro damage characteristics of fractured sandstone under variable upper limit cyclic loading and unloading, and provide a reference for scientific evaluation of engineering stability.

     

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