针对砂土地层浅埋盾构隧道开挖面稳定性问题,利用编制的极限分析三维下限数值计算程序获取维持开挖面稳定的最小极限支护压力,并与极限分析上限法、极限平衡法及模型实验结果进行对比分析,验证了所得支护压力为极限分析理论框架内的较优解答。结果表明:本文所提极限分析三维下限数值分析方法可直接获取开挖面极限支护压力和失稳形态,摆脱了破坏模式的限制,且具有较高的计算精度;内摩擦角显著影响开挖面前方地层破坏模式以及极限支护压力的变化规律;内摩擦角较小时,开挖面前方地层整体失稳,极限支护压力随着埋深比增大而增大;内摩擦角较大时,开挖面前方地层仅局部失稳,支护压力几乎不受埋深比影响;极限支护压力在不同埋深比时均会随着内摩擦角的增加而降低。研究成果丰富了浅埋盾构隧道开挖面稳定性的理论成果,可为开挖面支护压力设计提供借鉴。
Aiming at the face stability analysis of shallow shield tunnel in sand, the minimum limit support pressure to maintain the face stability obtained by the rigorous three-dimensional lower bound numerical limit analysis calculation codes. The comparison among the calculated results, the upper bound method, the limit equilibrium method and the model test results verifies that the support pressure obtained by the proposed method is the better solution within the theoretical framework of limit analysis. The results show that: The proposed three-dimensional lower bound numerical limit analysis method in this article can directly obtain the ultimate support pressure and failure mechanism of tunnel face. The proposed method can also overcome the limitations from the preset failure mechanism and has high calculation accuracy. The results also show that the internal friction angle affects the failure mechanism of the stratum in front of the excavation face, and then affects the variation law of the ultimate support pressure of the excavation face. When the internal friction angle is small, the whole stratum in front of the excavation face will be unstable and the ultimate support pressure will gradually increase with the increase of the buried depth ratio; When the internal friction angle is large, the stratum in front of the excavation face only produces local instability, and the support pressure is hardly affected by the buried depth ratio. The ultimate support pressure will decrease with increased internal friction angle at different buried depth ratios. The research results further enrich the theoretical results of shield tunnel face stability, and can provide reference for the design of face support pressure in shallow shield tunnel construction.
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