With the development of urban construction, uplift pile has been widely used in underground structure bearing buoyancy. The pile is buried deep underground, and the foundation pit is excavated on the pile foundation, the stress redistribution of the soil after the foundation pit excavation will reduce the lateral stress of the pile at the bottom of the pit, resulting in the reduction of friction resistance, but this effect is limited to a certain depth at the bottom of the foundation pit. Referring to the unloading influence depth corresponding to the vertical unloading coefficient in the spring back calculation of foundation pit and introducing the unloading influence depth corresponding to the horizontal unloading coefficient, it is deduced that the relationship between the horizontal unloading coefficient and the vertical unloading coefficient is based on the friction angle. Based on the bearing capacity control and numerical simulation, it is determined that the corresponding depth when the horizontal unloading coefficient is 0.95 is the unloading influence depth. The depth to width ratio of excavation has a great influence on unloading influence depth, and the internal friction angle of soil has little influence on unloading influence depth, while the influences of pile diameter and pile-soil friction coefficient can be ignored. The formula of unloading influence depth is derived in this paper. Comparing the unloading influence depth of sand and soft soil, the unloading influence depth of sand is greater than that of soft soil.

The open-cut tunnels in Aixi Lake, Nanchang, are constructed in a condominium form of highway tunnel and subway tunnel, which are the first superimposed double-level tunnels in China. The scientific problems faced by this new structure form have attracted the attention of engineers and researchers. If this structure form can be reasonably used, it can reduce the repeated excavation of the ground and reduce the impact of highway tunnel construction on subway tunnels. It is of great guiding significance to study the influence of the spacing between lower double-track subway tunnels on the stress and deformation characteristics of the upper highway tunnel. Based on the model test, the deformation, axial force, bending moment, and earth pressure of the upper highway tunnel are studied. The results show that the maximum displacement of upper tunnel floor can be reduced by 30% when the spacing of the lower tunnel makes the center line of the lower single tunnel coincide with the quadripartite line of the upper tunnel. Horizontal spacing between lower double-track tunnels significantly influences the bending moment of upper tunnel floor but hardly influences the axial force of the upper tunnel floor. Considering the influence of lower tunnel spacing on the earth pressure of the upper tunnel floor, the spacing of the lower tunnel should not exceed 50% of the section width of the upper tunnel.

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