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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 tests were carried out to study the instability and ultimate supporting pressure of shield tunnel in dry and saturated silt. Through the remote control of the displacement of the excavated surface and soil, the relationship curve between the supporting pressure and the displacement of the excavation face and the failure mode when the excavation face reaches the active limit equilibrium state are obtained. The results of two groups of dry sand centrifuge model tests show that when the ratio of tunnel depth to tunnel diameter increases from 0.5 to 1, the failure mode of the excavation face changes from the overall collapse to the chimney, but the pressure of the limit support changes little. Experiments in saturated sand show that the ultimate support pressure increases significantly as the failure range in the horizontal direction of the excavation surface expands compared to that in the same depth of dry sand. The three-dimensional elasto-plastic finite element numerical simulation of the failure process of the excavation surface was carried out, and the pressure and failure mechanism of the limit support of the excavation surface was obtained. The obtained results are in good agreement with the experimental results. Through numerical simulation, the influence of soil strength parameters, tunnel depth and seepage on pressure of ultimate support is analyzed. The results show that under the condition of seepage flow, the failure area of excavation face and the limit support pressure are all larger than the case of no seepage. The limit support pressure decreases with the increase of internal friction angle and decreases with the increase of tunnel depth.