This paper establishes a novel full-process numerical simulation framework for analyzing the 3D seismic response of mountain tunnels induced by active faults. The framework employs a two-step approach to achieve wavefield transmission through equivalent seismic load: first, a highly efficient and accurate FMIBEM (Fast multipole indirect boundary element method) is used for large-scale 3D numerical simulations at the regional scale to generate broadband ground motions (1-5 Hz) for specific sites; subsequently, using the FEM (Finite element method), a refined simulation of the plastic deformation of surrounding rock and the elastoplastic behavior of the tunnel structure was conducted at the engineering scale. The accuracy of the framework has been validated. To further demonstrate its effectiveness, the framework is applied to analyze the impact of different fault movement mechanisms on the damage to mountain tunnels based on a scenario earthquake (Mw 6.7). By introducing tunnel structure damage classification and corresponding damage indicators, the structural damage levels of tunnels subjected to active fault movements are quantitatively evaluated. The findings demonstrate that the framework successfully simulates the entire process, from fault rupture and terrain amplification to the seismic response of tunnel structures. Furthermore, the severity of tunnel damage caused by different fault types is ranked as follows: reverse fault > normal fault > strike-slip fault.

This study proposes a rapid seismic resilience assessment framework of tunnels in mountain regions considering the topography amplification effect and tunnel-soil dynamic interaction based on the indirect boundary element method (IBEM) coupled with the finite element method (FEM). The high efficiency is achieved by using a surrogate model to determine the tunnel fragility curves. This model reflects the relationship between the geometric and material variables of mountains and tunnels, as well as the tunnel damage index. To obtain the surrogate model, the identification of model variables is first explored quantitatively based on the random forest algorithm due to the high variable quantity. The dataset for training and testing the random forest is constructed from 600 numerical simulations. The IBEM-FEM coupling scheme is employed to describe the large-scale site response for tunnel damage analysis and significantly reduce the number of finite element grids for each sample. This scheme solves the nonlinear dynamic response of mountain tunnels under near-fault earthquakes. The surrogate model is then used to obtain the tunnel functionality and resilience. Based on the proposed framework, the influence of the mountain material, mountain height-span ratio, and tunnel position on the seismic fragility, functionality, and resilience are investigated. The results reveal that a surrogate model can be employed to replace a series of nonlinear time-history analyses of tunnels, with a high accuracy and efficiency. The shear modulus of the surrounding rock, the height-to-span ratio of the mountain, and tunnel position have a significant impact on tunnel fragility and resilience. This impact is correlated with the tunnel height. The mountain topography can cause a difference of approximately 20 % in the tunnel resilience.

A profound understanding of the interaction between loess slopes and tunnels, along with the mastery of protective measures for tunnels crossing loess slopes, is crucial for ensuring the excavation and operation safety of tunnels in loess slope areas. This article summarizes research findings on the loess slope-tunnel system, concentrating on sources triggering failures, the acting mechanism of failures, and strategies for failure mitigation. Loess slopes, serving as the tunnel's bearing medium, may suffer from engineering disturbances during construction and operation, significantly affecting their stability. This is reflected in the intensification of crack formation, water infiltration, and vibration propagation in the slope. The degree of slope-tunnel interaction depends on relative spatial positioning, slope characteristics, and construction parameters. Although extensive research has focused on tunnel deformation in orthogonal systems, oblique systems require additional investigation. At different stages, preventing failure involves three levels: proactive avoidance, proactive mitigation, and passive reinforcement. Traditional approaches involve divide and conquer, but considering tunnels and slopes as an integrated whole is an emerging research area. Innovative technologies, like Negative Poisson's ratio anchor cables and Steel-Concrete Composite Support for challenging loess terrains, are introduced. Applying these technologies in practical engineering is recommended to accumulate experience and support their mature application. This review can offer valuable support for designing, operating, and managing tunnels crossing areas prone to loess landslides.