Optimization Analysis of Initial Support Parameters for Highway Tunnel Construction in a Faulted and Fractured Zone

To effectively ensure the construction stability in the faulted and fractured zone of a tunnel, the initial support parameters in the composite lining should be optimized. Based on a faulted and fractured zone of a highway tunnel, this paper uses FLAC3D finite difference software to establish a numerical model for tunnel excavation using the two-bench excavation method. Based on the stability criterion of displacement method, the effects of initial support parameters such as sprayed concrete thickness, extending bolt length and bolt circumferential spacing, and bolt row spacing on the stability of the surrounding rock in the faulted and fractured are analyzed. The analysis shows that increasing the sprayed concrete thickness, extending bolt length and reducing the bolt row spacing and bolt circumferential spacing can reduce the settlement of the vault of the surrounding rock and significantly improve the stability of the surrounding rock. Considering the construction safety, construction difficulties, and economic factors, it is recommended to adjust the sprayed concrete thickness, bolt length, bolt circumferential spacing, and bolt row spacing in the faulted and fractured zone to 0.3, 4.0, 0.8, and 0.8 m, respectively.