为探究砂土地层盾构隧道垂直下穿既有管道过程中掌子面前方土体的被动失效区及极限支护压力的影响因素，首先，基于数值模拟方法，分析隧道掌子面与既有管道之间水平间距对前方土体被动失稳区及其极限支护压力的影响规律。在此基础上，将所得数值模拟最不利工况下的掌子面前方土体被动失效区域特征与极限平衡理论框架相结合，提出一种适用于隧道垂直下穿既有管道的三维极限平衡理论模型，该模型由上部倒棱台、既有管道和下部对数螺旋楔形体3部分组成，并系统推导相应工况下掌子面被动极限支护压力的计算公式。最后，通过理论解与数值模拟结果的对比，验证所提理论模型的准确性与适用性。研究结果表明： 1）当既有管线位于掌子面前方约隧道直径的水平距离处时，其对掌子面极限支护压力及前方土体破坏模式的影响程度最大； 2）土体内摩擦角、管道埋深及管隧间距对掌子面被动极限支护压力影响显著； 3）当内摩擦角较大时，支护压力随管隧间距呈正相关增长； 4）在小内摩擦角条件下，管隧间距变化对支护压力的敏感性显著降低。
The authors investigate the
influencing factors of the passive failure zone and the ultimate face support
pressure ahead of the tunnel face during shield tunneling beneath existing
pipelines in sandy soil layers. Numerical simulations are first conducted to
evaluate the effect of the horizontal distance between the tunnel face and the
existing pipeline on the development of the passive failure zone and the
corresponding ultimate support pressure. Based on the critical conditions
identified through simulation, a three-dimensional
limit equilibrium model is proposed. This model, applicable to tunnel face
behavior during vertical under-crossing of existing
pipelines, comprises three components: an upper inverted frustum, the existing
pipeline, and a lower logarithmic spiral wedge. A closed-form solution for calculating the ultimate passive support pressure
is then derived. The model′s validity is confirmed by
comparing theoretical predictions with numerical simulation results. The
findings reveal that: (1) The impact on the failure mechanism and ultimate
support pressure is most significant when the pipeline is located approximately
one tunnel diameter ahead of the face. (2) The soil internal friction angle,
pipeline burial depth, and tunnel-pipeline spacing
markedly affect the passive support pressure. (3) With higher internal friction
angles, the support pressure increases as the vertical clearance between the
tunnel and pipeline grows. (4) With lower friction angles, the support pressure
becomes much less sensitive to changes in vertical clearance.
