Theoretical Study on Soil Deformation during the Construction of Composite Strata Overlapping Shield Tunnels

Theoretical research is conducted on the soil deformation caused by the construction of overlapping tunnels under composite geological conditions. Based on the theoretical method of combining analogous considering the shielding effect of the stochastic medium theory and the three-dimensional unified solution, a computational model was established considering the shielding effect of the underground tunnel on the deformation of the upper tunnel is taken into account. The calculation formula for soil deformation was derived. The theoretical method in this article was applied to multiple sets of measured cases for verification. Research indicates that: The calculation results have a good degree of fit, proving the feasibility of this method. Through single factor analysis, it is found that the soil conditions near the upper tunnel in overlapping tunnels have a significant impact on the deformation of surface soil. Compared to single line construction, the soil deformation caused by the upper tunnel in the overlapping tunnel from bottom to top is shallower and narrower due to the influence of the lower line shielding effect. The shielding effect coefficient proposed in this article can better reflect the influence of the lower line tunnel on the soil deformation of the upper tunnel. The magnitude of the shielding effect coefficient is inversely proportional to the distance between the tunnel axes, and the smaller the tunnel spacing, the greater the shielding effect coefficient.