The stability of excavation face in shield tunneling plays a key role for construction safety. The ignorance of soil anisotropy in most previous studies would induce inaccurate stability assessment. This paper studies the failure of shield tunnel face in cross-anisotropic granular media by physical model tests and discrete element simulation. Model tests were carried out on the tunnel face stability in anisotropic granular media, and initial anisotropy was generated by controlling the long axis of non-spherical particles. By conducting image analysis on the picture taken by HD camera, the failure mode of tunnel face was obtained. It consists of a sliding wedge and an overlying loosen area, and the inclination angle of sliding wedge varies with the bedding plane. The variation in limit support pressure with the intersection angle of the shield tunneling direction and the soil bedding plane was obtained. Discrete element simulation was further employed to study the tunnel face stability in cross-anisotropic granular media; the microscopic parameters were calibrated by fitting against the particle drop test and repose test. Clump particle consisted of three identical ball was used in the simulations, and its long and short axes were in accordance with rice particles. The obtained varying characteristic of limit support pressure with intersection angle from simulation is consistent with the test results, and the obtained failure mode is also similar to that of physical model test. The principal stress distribution at failure state was analyzed in the discrete element simulation, and the change of major principal stress direction from vertical to nearly horizontal in the loosen area clearly shows the formation of soil arches.

中文翻译：

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各向异性粒状介质中盾构隧道面稳定性的物理模型试验和离散元模拟

盾构隧道开挖面的稳定性对施工安全起着关键作用。在大多数先前的研究中，对土壤各向异性的无知将导致不正确的稳定性评估。本文通过物理模型试验和离散元模拟研究了横观各向异性粒状介质中盾构隧道面的破坏。在各向异性粒状介质中对隧道面稳定性进行了模型测试，并通过控制非球形颗粒的长轴产生了初始各向异性。通过对高清摄像机拍摄的图像进行图像分析，得出隧道面的破坏模式。它由一个滑动楔块和一个上方的松动区域组成，并且滑动楔块的倾斜角度随垫层平面而变化。得到了极限支撑压力随盾构掘进方向与土壤层理平面相交角的变化。进一步利用离散元模拟研究了横观各向异性粒状介质中的隧道面稳定性。微观参数通过与颗粒滴落试验和静止试验拟合来校准。模拟中使用了由三个相同的球组成的团块粒子，其长轴和短轴与大米粒子一致。通过仿真得到的极限支撑压力随交角的变化特性与试验结果吻合，其失效模式也与物理模型试验相似。通过离散元模拟分析了失效状态下的主应力分布，