浅覆盾构隧道环向挤出破坏上限有限元分析

Blow-out Failure Analysis for Shallow Shield Tunnel with Finite Element Upper Bound Method

针对软弱地层浅覆盾构隧道未支护段地层挤出破坏问题,基于极限分析上限有限元法,结合节点可动的刚体平动运动单元,建立了隧道环向开挖面挤出破坏的非线性规划模型并编程求解。通过参数敏感性分析,研究了地层参数、隧道埋深等因素与临界加载系数间的曲线关系,并探讨了刚性块体体系破坏模式的演化特征。结果表明,临界加载系数σT/c随φ、γD/c和C/D的增加而增加;φ对地层破坏模式影响显著,φ值越大,滑动面与竖向夹角越大;刚体平动运动单元法能使单元间的速度间断线自动调整至最佳方位,利用较少的单元可获得较好的上限解,并清晰的反映出土层破坏形态。

To study blow-out failure rules of shallow shield tunnels,based on the finite element upper bound method,a nonlinear programming model is built and solved with rigid translator moving elements. Then,through the analysis for sensitivity of parameters about the model,the relations between the critical loading coefficients and influence factors,such as formation parameters and buried depth,are studied. Meanwhile,the failure modes of rigid system are also explored with the program. The results show that the critical loading coefficients σT/ c increase with increment of φ,γD / c and C / D; the φ has great influence on failure mechanism of the strata. Failure area expands when φ increases. The velocity discontinuities of elements can be adjusted automatically into the best directions by this method,to acquire a good upper bound solution and a clear failure mechanism with a few elements.