Semi-analytical solution for mechanical analysis of tunnels crossing strike-slip fault zone considering nonuniform fault displacement and uncertain fault plane position

The tunnel subjected to strike-slip fault dislocation exhibits severe and catastrophic damage. The existing analysis models frequently assume uniform fault displacement and fixed fault plane position. In contrast, post-earthquake observations indicate that the displacement near the fault zone is typically nonuniform, and the fault plane position is uncertain. In this study, we first established a series of improved governing equations to analyze the mechanical response of tunnels under strike-slip fault dislocation. The proposed methodology incorporated key factors such as nonuniform fault displacement and uncertain fault plane position into the governing equations, thereby significantly enhancing the applicability range and accuracy of the model. In contrast to previous analytical models, the maximum computational error has decreased from 57.1% to 1.1%. Subsequently, we conducted a rigorous validation of the proposed methodology by undertaking a comparative analysis with a 3D finite element numerical model, and the results from both approaches exhibited a high degree of qualitative and quantitative agreement with a maximum error of 9.9%. Finally, the proposed methodology was utilized to perform a parametric analysis to explore the effects of various parameters, such as fault displacement, fault zone width, fault zone strength, the ratio of maximum fault displacement of the hanging wall to the footwall, and fault plane position, on the response of tunnels subjected to strike-slip fault dislocation. The findings indicate a progressive increase in the peak internal forces of the tunnel with the rise in fault displacement and fault zone strength. Conversely, an augmentation in fault zone width is found to contribute to a decrease in the peak internal forces. For example, for a fault zone width of 10 m, the peak values of bending moment, shear force, and axial force are approximately 46.9%, 102.4%, and 28.7% higher, respectively, compared to those observed for a fault zone width of 50 m. Furthermore, the position of the peak internal forces is influenced by variations in the ratio of maximum fault displacement of the hanging wall to footwall and the fault plane location, while the peak values of shear force and axial force always align with the fault plane. The maximum peak internal forces are observed when the footwall exclusively bears the entirety of the fault displacement, corresponding to a ratio of 0: 1. The peak values of bending moment, shear force, and axial force for the ratio of 0:1 amount to approximately 123.8%, 148.6%, and 111.1% of those for the ratio of 0.5:0.5, respectively.