浅埋隧道盾构掘进地层挤出破坏形态与临界压力上限有限元分析

采用上限有限元方法分析地层参数(土体重度,内摩擦角,黏聚力)、隧道埋深与直径、土体剪胀效应等因素综合影响下浅埋隧道盾构掘进地层挤出破坏模式与临界压力。研究表明:临界压力系数随内摩擦角增大而增大,且重度比越大临界压力系数增大得越明显;临界压力系数随重度比和埋深比的变化基本呈线性增长;内摩擦角较大时,耗散能密度呈斜向条带状分布,地层向上隆起破坏范围较大;重度比较大时,耗散能密度呈更窄更集中的斜向条带状分布,至地表有所发散;埋深比越大,剪切带起始位置越靠下,并在隧道斜上方弯曲程度越大;地层挤出破坏区域主要出现在隧道正上方,地表鼔出近似呈倒置锅底状,隧道正上方至地表一定范围内地层整体向上运动,斜向上方向变形最大。

Upper Bound Finite Element Analysis on Stratum Squeeze Failure Form and Critical Pressure in Shield Tunneling of Shallow Tunnel

The upper bound finite element method was used to analyze the stratum squeeze failure form and critical pressure in shield tunneling of shallow tunnel under the comprehensive influence of formation parameters(soil weight,internal friction angle,cohesion),tunnel buried depth and diameter,soil dilatancy effect and other factors.The results show that the critical pressure coefficient increases with the increase of internal friction angle,and the larger the gravity ratio is,the more obvious the critical pressure coefficient increasement is.The critical pressure coefficient increases linearly with the change of gravity ratio and buried depth ratio.When the internal friction angle is large,the dissipative energy density is distributed in inclined strip and the upwelling failure range is large.When the gravity ratio is large,the dissipative energy density presents a narrower and more concentrated inclined strip distribution,and diverges to the surface.The larger the buried depth ratio is,the lower the starting position of the shear zone is,and the greater the bending degree above the tunnel slope is.The stratum squeeze failure area is mainly above the tunnel,the surface swelling appears as an inverted pot bottom,and the whole stratum moves upward in some range from the top of the tunnel to the surface,with the largest deformation in the oblique upward direction.