结合南京某越江隧道工程，建立了模拟盾构隧道开挖面失稳过程的数值模型，研究了越江盾构隧道开挖面失稳过程中土体应力变化以及由土体应力重分布引发的土拱效应。研究表明： 沿埋深由下至上，土体竖向应力随开挖面位移的增大先减小后保持不变，水平应力先减小后略微增大； 土体侧压力系数沿埋深由下至上先增大后减小； 随开挖面位移增大，开挖面前方局部土体竖向应力和水平应力同时减小，形成失稳破坏区； 失稳破坏区上部土体竖向应力减小，水平应力增大，形成拱顶区； 失稳破坏区四周土体竖向应力增大，水平应力减小，形成拱脚区，土拱效应逐渐发挥。

In this paper, a numerical model simulating the process of the failure of the tunnel face in shield tunneling is established on basis of a rivercrossing tunnel in Nanjing, China, and the change of the soil stress and the soil arch effect accompanied by its redistribution is studied. It’s revealed that from the bottom up, as the excavation face’s displacement increases, the vertical stress of the soil decreases before it keeps stable later, while the horizontal stress decreases before it rises slightly. As the tunnel cover becomes smaller, the coefficient of the lateral pressure of the soil increases before it decreases later. When the displacement of the excavation face becomes serious, both the vertical stress and the horizontal stress ahead of the excavation face decrease. Thus the buckling failure zone is formed. The vertical stress of the soil on top of this zone becomes lower, and the horizontal stress of the soil on top of this zone becomes higher, thus the vault area is formed. The vertical stress of the soil around the buckling failure zone becomes higher, and the horizontal stress of the soil around the buckling failure zone becomes lower, thus the arch foot area is formed and the soil arch effect gradually comes into effect.