In this paper, numerical simulations of face stability of shallow tunnels are carried out by using the particle discrete element codes PFC^2D from the microscopic view. Progressive instability of the tunnel face is achieved through the withdrawal of the baffle used to simulate the tunnel face. Under different retreating displacement of the tunnel face, the evolution laws of support pressure on the tunnel face, the ground deformation, ground surface settlement and contact force chain in front of the tunnel face are studied. The results show that with the withdrawal of the tunnel face, the support pressure on the tunnel face can be divided into four stages, namely, the rapid decline stage, the minimum stage, the slow rising stage, and the horizontal stability stage. Moreover, based on the simulation results of the particle contact force chain, discriminated methods of failure zones are proposed. The research results obtained from this paper will provide theoretical support for the reasonable value of support pressure of a tunnel face in practical engineering.

中文翻译：

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基于粒子流代码的二维隧道掘进面稳定性数值模型

本文利用粒子离散元代码PFC ^2D对浅埋隧道的工作面稳定性进行了数值模拟。从微观上看。通过撤出用于模拟隧道面的挡板，可以实现隧道面的渐进式不稳定性。研究了不同回采位移下巷道支护压力的演化规律，地表变形，地表沉降以及巷道前部的接触力链。结果表明，随着巷道面的撤出，巷道面的支护压力可分为快速下降阶段，最小阶段，缓慢上升阶段和水平稳定阶段四个阶段。此外，基于粒子接触力链的仿真结果，提出了失效区域的判别方法。