盾构隧道环向开挖面破坏机制及剪胀效应研究

Failure mechanism of shield tunnel circumferential excavation face and the influence of the dilatancy effect on the tunnel stability

采用刚性滑块构建两种圆形隧道失稳环向开挖面破坏模式,利用编制的非线性规划程序求解隧道失稳环向开挖面支护力系数σT/c(σT为均布支护荷载,c为有效黏聚力)最优上限解及地层破坏模式,揭示地层参数对隧道稳定性的影响,提出简单实用的极限支护力简化公式。研究结果表明:不排水条件下,当隧道埋深比H/D(H为埋深,D为隧道直径)和重度系数γD/c(γ为重度)较小时,破坏区域主要集中在隧道中上部,随着H/D和γD/c增大,滑移线起始位置沿着隧道轮廓逐渐向隧道底部扩展,破坏区域向水平方向扩展。排水条件下,地层破坏模式主要有3种。当内摩擦角φ和γD/c较大时,随着剪胀系数的减小,极限支护力和地层破坏范围变化较大,甚至可能引起破坏模式的改变。针对不同深度提出的极限支护力简化公式可快速获得隧道环向开挖面极限支护力。

Rigid sliding blocks are used to construct two failure modes of the tunnel’s circumferential excavation surface of circular tunnel. The compiled nonlinear programming program is used to solve the optimal upper bound solution of the support force coefficient σT/c(σT is uniformly distributed support load and c is the effective cohesion) and the stratum failure mode so as to reveal the influences of stratum parameters on tunnel stability. A simple and practical simplified formula for the ultimate support force of the tunnel’s circumferential excavation surface is proposed. For undrained condition, the failure region is mainly concentrated in the upper part of the tunnel when the tunnel depth ratio H/D(H is the buried depth and D is the tunnel diameter) and the gravity coefficient γD/c(γ is unit weight) are small. With the increase of H/D and γD/c, the starting position of the slip line gradually expands to the bottom of the tunnel along the tunnel contour, and the failure region expands to the horizontal direction. For drainage conditions, there are three main stratum failure modes. When the internal friction angle φ and γD/c are large, with the decrease of the dilatancy coefficient, the ultimate supporting force increases significantly, and the range of failure region varies greatly, which may even cause a change in the failure mode. The ultimate supporting force of the tunnel circumferential excavation surface can be quickly obtained through the proposed simplified formulas.