Mechanical Response and Stability Optimization of Shallow-Buried Tunnel Excavation Method Conversion Process Based on Numerical Investigation

Different excavation methods lead to substantial changes in the relaxation zone of the surrounding rock. The stress characteristics of the support structure become more complex during the process of excavation method conversion. It is essential to design a well-considered construction plan to minimize the disruptions caused by excavation method conversion. This work takes a tunnel in Jiangsu Province, China, as the engineering background and establishes a numerical model for the conversion from the double-side-drift method to the three-bench method. Based on a numerical investigation, this study analyzed the deformation of surrounding rock and the stress state of the support structure during the excavation method conversion. The results showed that excavation method conversion can accelerate the deformation rate of the surrounding rock, causing the support structure to bear greater pressure. This leads to a significant increase in the circumferential stress at the junction of two excavation methods. Setting up a reinforced area during the process of excavation method conversion can improve the stress state of the support structure. Finally, an analysis of the parameters of the reinforced area was conducted, and a reasonable construction plan was proposed. This study can provide guidance for subsequent construction projects.

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