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盾构法隧道施工过程中，土体密实度对开挖面极限支护力值与稳定性影响是一个非常重要的因素。基于Kirsch室内模型试验，采用颗粒流计算分析了隧道掘进过程中土体密实度对开挖面极限支护力、残余支护力以及开挖面前方土体孔隙比变化的影响，从细观角度解释了砂土中盾构隧道开挖面失稳机理，分析了砂土中盾构隧道掘进时土体破坏形态与分布范围；进而提出了计算开挖面极限支护力的改进楔形体分析模型。研究成果可为盾构隧道施工中分析开挖面的稳定提供参考。“,”The soil density is a key factor for the studies on the limit support pressure and the face stability operation during tunneling construction. Based on the Kirsch’s laboratory model tests, the PFC2D is employed to investigate the influence of soil density on the limit support pressure, residual support pressure and void ratio in the heading face. The failure mechanisms of the excavation face are investigated at the mesoscopic level. The failure behavior and arrange of the face stability of the shield tunnels in sand are analyzed. The improved wedge model is proposed as a method for calculating the limit support pressure of face. It may provide certain guidance to the stabilization of excavation face of shield tunnels.