Research on the Influence of Tunnel Invert Excavation on the Rheological Deformation of Different Levels of Surrounding Rock

The surrounding rock in the closed section of the inverted arch creates a bearing ring that, when combined with the upper initial support, provides stable initial support. However, excavation of the inverted arch can disrupt the original balance and significantly impact the tunnel’s stability. Using the classic Burgers creep constitutive model, we conducted numerical analyses of the construction process for tunnels with different closure and exposure distances of the inverted arch under varying levels of surrounding rock, using the three-step excavation method. We compared the maximum displacement of the arch crown to study the influence of the closure and exposure distances of the inverted arch on the stability of the initial support lining. Our results show that the displacement of the arch crown is primarily influenced by the strength of the surrounding rock; the lower the strength of the rock, the greater the displacement of the arch crown. Furthermore, the displacement of the arch crown increases as the closure distance of the inverted arch increases. Conversely, the exposure distance of the inverted arch has a minimal impact on arch displacement, and the longer the exposure distance, the greater the arch displacement. These findings can serve as a foundation for improving existing standards and adapting them to the spatial requirements of large-scale mechanized operations.