To enhance the economic and safety aspects of tunnel structural design, this study optimizes the mix proportion of steel fiber-reinforced concrete (SFRC). It investigates the stress characteristics and support parameters of SFRC secondary lining structures via small-scale model tests and finite element analysis. The research focuses on the cracking process, deformation, and stress characteristics of SFRC linings under various loads. Compared with conventional reinforced concrete tunnels, SFRC tunnels show a significant increase in lining stiffness and load capacity, with a 20% reduction in reinforcement yielding load. When the damage factor is 0.43, the addition of steel fibers increases compressive stress by 22.18%. Using ABAQUS, simulations of SFRC linings with thicknesses ranging from 400 mm to 600 mm and reinforcement ratios of 0% to 0.28% were conducted. The results indicate that a 450 mm thick SFRC lining matches the mechanical performance of a 600 mm thick conventional reinforced concrete lining. Notably, an SFRC lining with a 0.20% circumferential reinforcement ratio equals a conventional lining with a 0.28% reinforcement ratio in overall mechanical performance.

This study investigates the influence of freeze–thaw (F–T) cycles on the seismic fragility of double-column bridge piers. Mechanical tests were conducted on standard concrete specimens subjected to 0, 25, 50, 75, and 100 F–T cycles using an HC-HDK9/F rapid freeze–thaw testing machine. The experimental results were used to calibrate and validate the applicability of the selected concrete constitutive model. A nonlinear finite element model of a double-column bridge pier was developed in the OpenSees platform, incorporating material degradation parameters corresponding to varying F–T cycles. Incremental dynamic analysis (IDA) was performed to derive seismic demand curves and quantify fragility corresponding to multiple damage states. The results indicate that the failure probability of the piers increases significantly with the number of F–T cycles, particularly for slight and moderate damage levels. In the low to moderate peak ground acceleration (PGA) range, the exceedance probabilities for slight and moderate damage states show a sharp rise, highlighting the sensitivity of early-stage damage to F–T degradation. It is worth noting that under the extreme condition of PGA = 1.0 g and 100 freeze–thaw cycles, the piers still exhibit a certain degree of redundancy against severe and complete damage, which to some extent reflects the certain rationality of the current seismic design in freeze–thaw environments. These findings underscore the robustness of current seismic design provisions in cold regions and provide theoretical and data-driven support for performance assessment, service life prediction, and maintenance planning of bridges exposed to freeze–thaw environments.

Excavations in urban cores, in close proximity to existing structures, can significantly influence the structural loading. This study, based on a specific section of the foundation pit for the Yaoziqiu area road network project, constructs a mechanical analysis model to assess the impact of foundation pit construction on adjacent buildings. The research examines how various factors, including the distance between the building and the pit, pile length, retaining wall thickness, and the depth of the retaining wall’s embedment, affect the deformation response of the structures. The results indicate that when the building is 5 m away from the foundation pit, the maximum pile foundation settlement is 13.45 mm. When the distance is 30 m, the settlement value is 6.91 mm, with a decrease of 6.54 mm. The effect of foundation pit excavation on pile foundation settlement is significantly reduced when the pile length exceeds 15 m. When the thickness of the retaining wall increases from 0.5 m to 0.7 m, the maximum settlement of the building foundation is reduced by 1.34 mm, a decrease of 8.38%. When the thickness increases from 0.9 m to 1.1 m, the maximum settlement of the building foundation is reduced by 0.6 mm, a decrease of 4.17%. When the embedded depth of the retaining structure increases from 10 m to 15 m, the maximum settlement is reduced by only 1.05 mm. When the embedded depth is increased to 25 m, the change in the settlement value of the building foundation is within 0.2 mm. This study offers a detailed quantitative analysis of the factors influencing structural deformation, providing specific guidance for developing risk minimization strategies in planning excavations near existing structures.