Abstract The tunnel instability accidents caused by surcharge loading could even lead to ground settlement or collapse, damage to the existing municipal pipelines or inclination of the surgical buildings. Series of large-scale physical model test was conducted in this paper to reveal the failure mechanism of tunnel in soft rock subjected to surcharge loading. The non-contact full-field displacement measurement (i.e. Digital Image Correlation, DIC) was employed to obtain a detailed deformation of surrounding rock after excavation. A coupled numerical method combing the continuum (Finite Difference Method, FDM) and dis-continuum (Discrete Element Method, DEM) analysis was used to deal with the failure mechanism of tunnel excavation in rock mass. Good agreements between physical model test and numerical analysis approve the accuracy of the proposed FDM-DEM numerical model. It is found that the collapse mainly occurred in tunnel roof rather than in tunnel sidewall. The collapse zone shows a step-type increase with the increase of surcharge loads. The stress loosening zone (SLZ) in tunnel roof is larger than that in tunnel sidewall. The thickness of SLZ in tunnel roof can be used to design the length of the formed pressure anchors. The proposed large-scale model test with DIC method is applicable to the tunnel engineering study. Moreover, the results in this paper give some insights to secure excavation works and optimize supporting structures.

中文翻译：

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超载作用下软岩浅埋隧道失稳机理

摘要 超载引起的隧道失稳事故甚至可能导致地面沉降或坍塌、现有市政管线破坏或手术楼倾斜。本文进行了一系列大型物理模型试验，揭示了超载荷载作用下软岩隧道的破坏机理。非接触式全场位移测量（即数字图像相关，DIC）用于获得开挖后围岩的详细变形。采用连续体（Finite Difference Method，FDM）与非连续体（Discrete Element Method，DEM）分析相结合的耦合数值方法处理岩体隧道开挖破坏机理。物理模型测试和数值分析之间的良好一致性证明了所提出的 FDM-DEM 数值模型的准确性。发现坍塌主要发生在隧道顶板，而不是隧道侧壁。随着超载荷载的增加，塌陷区呈阶梯式增加。隧道顶板应力松散带（SLZ）大于隧道侧壁应力松散带。隧道顶板SLZ的厚度可用于设计成型压力锚杆的长度。提出的大尺度模型试验 DIC 方法适用于隧道工程研究。此外，本文的结果为确保开挖工程和优化支撑结构提供了一些见解。随着超载荷载的增加，塌陷区呈阶梯式增加。隧道顶板应力松散带（SLZ）大于隧道侧壁应力松散带。隧道顶板SLZ的厚度可用于设计成型压力锚杆的长度。提出的大尺度模型试验 DIC 方法适用于隧道工程研究。此外，本文的结果为确保开挖工程和优化支撑结构提供了一些见解。随着超载荷载的增加，塌陷区呈阶梯式增加。隧道顶板应力松散带（SLZ）大于隧道侧壁应力松散带。隧道顶板SLZ的厚度可用于设计成型压力锚杆的长度。提出的大尺度模型试验 DIC 方法适用于隧道工程研究。此外，本文的结果为确保开挖工程和优化支撑结构提供了一些见解。