The overburden of shield tunneling in the shallow ground can lead to the passive destruction of soil in front of the excavation surface

resulting in surface uplifts.Based on the silo theory

and by optimizing the traditional three-dimensional wedge model

a three-dimensional（3D）soil failure calculation model（Modified 3D wedge model）was established for wedge-shaped block and chamfering platform

and the formula of passive limit supporting force was deduced.The fracture-rupture angleβwas analyzed at different depths.The finite element analysis software Midas-GTS was used to simulate the passive failure of the excavation face of shield tunnel to reveal the variation and failure mode of the passive supporting force.The results indicate that the proposed calculation model agrees well with the passive failure mode of soil at the excavation surface.By analyzing the fracture angleβ

the optimal solution is about 30° when the soil fails passively.Furthermore

S/（γD）increases nonlinearly with the increase of internal friction angleφ.The larger the depth K

the more obvious the amplitude will be.In the failure mode analysis

under a small Kvalue

soil deformation is more sensitive to S/（γD）

and the excavation surface is more prone to passive failure.When passive failure occurs

the longitudinal displacement of soil is greater than that of the lateral displacement.