Limit support pressure of shield excavation face under-crossing the existing metro station

With the progression of urban development, the occurrence of shield tunnels intersecting existing transportation hubs has become increasingly prevalent. When a tunnel is constructed beneath an existing station, the stress distribution within the surrounding soil is altered, leading to variations in the support pressure at the excavation face of the shield tunnel. However, the current literature lacks a calculation method for determining the support pressure at the excavation face in such scenarios. This research utilizes three-dimensional finite element numerical simulations to examine the soil responses associated with a shield tunnel that under-crossing an existing metro station situated within a typical clay-gravel stratum. The study specifically addresses the failure of the excavation face at varying distances from the existing station. The analysis encompasses the support pressure at the excavation face, soil displacement and stress, as well as the three-dimensional failure model. Based on the findings from the numerical simulations, a modified formula for calculating overburden earth pressure is proposed, which incorporates the influence of the overlying station. Following this modification, the relative error in the calculation of overburden earth pressure is reduced from 67.4% to 3.9%. Furthermore, when the modified formula is applied to assess the overburden earth pressure within a three-dimensional wedge-prism model of the clay-gravel strata, the relative error in the calculation of limit support pressure is decreased from 8.7% to 0.5%. The proposed modified formula for overburden earth pressure serves as a significant reference for determining the limit support pressure of the excavation face when a tunnel under-crossing the existing station.