Analysis of Longitudinal Non-Uniform Settlement of Tunnel Through Soft and Hard Mutation Strata

Under the influence of external construction factors, uneven settlement is easy to occur in shield tunnel in longitudinal soft and hard mutation stratum, which leads to such diseases as cross-platform between segment and ring, bolt shearing and joint leakage. For further study of the external factors on the shield tunnel longitudinal soft mutation formation in the influence of the vertical displacement, tunnel vertical displacement formula was derived under arbitrary load based on Winkler elastic foundation beam theory, and stack size on the ground, and the size of the stack, and vertical displacement of the tunnel buried depth of shield tunnel analysis combined with Boussinesq solution. A section of Xiamen Metro Line 2 is taken as an engineering example to verify the rationality of the theoretical formula. The results show that the vertical displacement curves of most shield tunnels follow the normal curve distribution under ground overloading, and the vertical displacement of shield tunnels in soft soil area is generally greater than that in hard soil area. The effect of the loading length on the maximum vertical displacement is limited. When the loading length exceeds a certain limit, the maximum vertical displacement does not increase, but the range of vertical displacement will expand accordingly. When the load width exceeds a certain limit, the vertical displacement curve does not change. When the buried depth is relatively shallow, the vertical displacements on both sides of the shield tunnel at the interface of soft and hard soil have little difference, but there is uplift phenomenon in the soft soil area. With the increase of the buried depth, the maximum vertical displacement of the tunnel gradually shifts to the soft soil area. The research results can provide a reference for the design of metro shield tunnel longitudinal through soft and hard mutation soil layer.