Watery strata and the influence of pore water pressure cannot be ignored when calculating the deformation of existing tunnels induced by the excavation of new undercrossing tunnels. Many parameters can affect the deformation of existing tunnels during the excavation of a new undercrossing tunnel. In this work, an optimized method was developed for calculating the settlement of an existing tunnel undercrossed by a newly excavated tunnel in water-rich strata. This method includes a deterministic calculation model and a probability analysis model. Based on the constitutive behavior of the soil and the poroelasticity theory, the excess pore water pressure at the axis of the existing tunnel was obtained and used in the deterministic calculation model, which computes the deformation of the existing tunnel. In addition, we established a probability model based on Kriging metamodeling, the Latin Hypercube sampling (LHS) and Monte Carlo sampling (MCS) methods, and conducted global sensitivity analysis (GSA) and failure probability analysis. The optimized parameters can be input into the deterministic model to make more accurate predictions. The optimized method was applied in and validated by a metro project in Beijing.

The artificial freezing method is commonly used in tunneling beneath overlying structures due to the significant development and utilization of underground space. However, there is a growing demand for controlling frost heave deformation in overlying structures and the interaction laws of these structures during freezing and undercutting remain unclear. Hence, a multi-physics coupling deformation calculation method is proposed. This study focuses on the shield tunneling project of Shanghai Metro Line 18 at Guoquan Road Station, which intersects with the existing upper operating station of Line 10. It investigates the construction approach for new tunnels during freezing, using the gray clay of layer ? 1 in Shanghai as the research target, particularly examining the disruptive effects on the primary structures of the upper operating station. Considering water migration, we derived the frost heave deformation formula and developed an improved thermo-hydro-mechanical coupling theory model by using pore ratio, freezing temperature, and average water pressure as coupling variables. Through frost heave tests on cohesive soil, we obtained the stress-strain relationship of frost heave specimens to describe the changes in pore structure. Subsequently, a thermo-hydro-mechanical three-field coupling numerical calculation was conducted using the weak form module (PDE) of COMSOL Multiphysics software. The simulation results closely matched the monitoring data and were below the predetermined control value, validating the accuracy of the enhanced coupling theory. These findings offer a multi-physics coupling approach for calculating deformations in similar frozen underpass tunnels, serving as a valuable reference for freezing method design and construction parameters. Additionally, we propose safety control indicators for reinforcement construction based on this scientific groundwork.