Abstract: To address the challenges of calculating soil deformation caused by the construction of a double-track horizontal shield tunnel under composite geological conditions, a model tailored for such tunneling operations is established. This model integrates a three-dimensional unified solution combined with the theory of quasi-random medium to derive calculation formulas for vertical and horizontal soil deformations. These formulas assess the impact of different geological conditions on tunneling-caused soil deformation. Soil-loss areas are divided using quasi-random medium according to geology, considering the influence of various geology on soil-loss areas and soil deformation. The prop-osed formulas are applicable to shield tunneling in composite strata, accounting for the effects of construction sequence and double-track interactions on soil deformation. The research results are summarized as follows: (1) The proposed formulas are feasible and applicable to double-track horizontal shield tunnels. (2) Horizontal soil deformation initially increases with soil depth and then decreases, with the maximum deformation occurring at the tunnel crown. The interaction between the double tracks leads to deviations in vertical and horizontal soil deformations. (3) Single-factor analysis of soil layer distribution at the excavation face, considering both upper-hard/lower-soft and upper-soft/lower-hard strata, reveals the following: As the proportion of hard soil increases, soil deformation exhibits a nonlinear change. Soil types with a larger proportion of soil-loss areas have a more significant effect on soil deformation. The settlement groove curve caused by double-track shield tunneling exhibits an extended vertical W shape that tends to flatten as the proportion of soft soil increases.

Key words: composite strata, double-track horizontal shield tunnel, soil deformation, analytical solution