Upper Bound Analysis of Stability of the Excavation Face of Shield Tunnel and Box Culvert Undercrossing Railway
In order to study the stability of excavation face during simultaneous construction of shield tunnel and box culvert and underpass railway,against the backdrop of the Xiamen Metro Line 6 shield tunnel and box culvert overlapping under the Haicang Railway Branch Line project,,FLAC3D was used to explore the excavation face model under active failure condition,and spatial discretization technology was used to construct the theoretical analysis model of excavation face active failure.Then,using the upper limit theorem of limit analysis,the limiting support force of excavation face under the failure mode is obtained by considering the supporting stress and train load.Finally,the theoretical solution is compared with the numerical solution.The results show that:①The excavation face failure mode of shield tunnel and box culvert is related to their buried depth ratio.When the buried depth ratio C/H of shield tunnel and box culvert is small,the deformation area of the two will form a connected area.With the increase of the C/H,the connected area will disappear,and the large deformation caused by instability is mainly reflected by the shield tunnel.② The theoretical model of excavation face failure under the instability of shield tunnel and box and culvert is compared with the numerical simulation,the difference is less than 10％,and the results are in good agreement,which verifies the rationality of the model.③The limiting support force when both shield tunnel and box culvert are unstable is close to that when the shield tunnel excavation face is unstable,and the limiting support force gradually decreases with the increase of the C/H,and finally tends to a constant value.
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