粉砂地层盾构隧道开挖面稳定性离心试验及数值模拟

通过开展离心模型试验，对干粉砂及饱和粉砂中盾构隧道开挖面的失稳破坏特性和极限支护压力进行了研究。通过远程控制开挖面土体位移，获得了支护压力与开挖面位移间的关系曲线及开挖面达到主动极限平衡状态时的破坏模式。2组干砂离心模型试验结果表明，当隧道埋深与隧道直径比从0.5增大到1时，开挖面破坏模式从整体坍塌破坏转变为烟囱状，但极限支护压力变化较小。饱和砂土中的试验表明，开挖面水平方向破坏范围相比在相同埋深干砂中的范围扩大，极限支护压力显著增加。对开挖面破坏过程进行三维弹塑性有限元数值模拟，获得了开挖面极限支护压力和破坏机制，所得结果与试验吻合较好。进一步通过数值模拟，分析了土体强度参数、隧道埋深及渗流对极限支护压力的影响规律。结果表明，渗流条件下开挖面破坏区域及极限支护压力均大于无渗流情况，极限支护压力随内摩擦角增大而减小，随隧道埋深增大而减小。

Centrifuge model test and numerical simulation of stability of excavation face of shield tunnel in silty sand

Through centrifugal model tests, the failure characteristics of the shield tunnel excavation face and the limit support pressure in dry and saturated silty sands are studied. By means of remote control of soil displacement, the relationships between the support pressure and the displacement of the excavation face are obtained, and the failure mode of the excavation face to the active limit equilibrium state is revealed. Two sets of dry silty sand centrifuge model test results show that when the ratio of tunnel depth to the tunnel diameter is from 0.5 to 1, the failure mode of the excavation face is changed from the whole collapse to funnel shape, but the change of of the limit support pressure is small. The test in saturated silty sand shows that the destruction extent in the horizontal direction of the excavation face is more than that at the same buried depth in dry sand, and the limit of the support pressure increases significantly. Three-dimensional elastoplastic finite element method is used to simulate the failure process of excavation face, and then the limit support pressure and failure mechanism of the excavation face are obtained. The numerical simulations are in good agreement with the experimental results. Additionally, the influence of the soil strength parameters, tunnel depth and seepage on the limit support pressure is further analyzed through the numerical simulation, it is shown that the damage area and the limit support pressure of the excavation face are larger than that of the nonseepage condition; the limit support pressure decreases with the increase of the internal frictional angle, and decreases with the increase of the tunnel depth.