Research on mechanical response of flysch tunnel construction and plastic damage mechanism of surrounding rock

This paper presents a numerical simulation study utilizing the DFN module to investigate the mechanical response of tunnel construction in the unique geotechnical environment of flysch. The study focuses on analyzing the displacement, stress, and strain characteristics of the tunnel surrounding rock, as well as the development of the plastic zone under different excavation depths and with or without inverts. The results reveal that flysch tunnels exhibit asymmetrical and dual mechanical response characteristics, with a dominant lateral pressure from the side walls. The stress-strain analysis indicates that the surrounding rock near the side walls experiences higher stress levels and concentrated plastic strain. Therefore, ensuring the stability of the side walls is crucial in flysch tunnel construction. Additionally, the mechanical properties of the surrounding rock depend on the proportion of high-strength and low-strength rocks, introducing a duality that contributes to the complex mechanical response mode of marble surrounding rock. These findings have significant implications for flysch tunnel construction and the control of surrounding rock stability.