As an attractive dielectric material, polyimide has been widely used in the field of electronics, aerospace, and automobiles due to its useful mechanical properties and good chemical resistance. UV irradiation was considered to be the main factor related to the damage and failure of polyimide. Here the effects of UV irradiation on the surface morphology and microscale mechanical properties of polyimide films are characterized by atomic force microscopy (AFM). The surface roughness of the UV-irradiated samples developed and the mechanical properties degraded with the radiation dose increased. For comparison, uniaxial tensile test was performed to obtain the macroscale Young’s modulus of polyimide film. The UV-irradiated damaging depth was simulated with finite element method (FEM).

Reinforced soil is widely used in the reinforcement of roadbeds, slope retaining walls, and other areas due to its excellent engineering performance. The interfacial friction strength between reinforcement and soil has a significant impact on the overall integrity and stability of the retaining structures. To investigate the interface friction characteristics of different reinforced soils, pull-out tests are conducted using a self-made pull-out apparatus on four types of reinforced soils: clay-geogrid, clay-carbon fiber cloth, clay-geocell, and gravel soil-geocell. Among the tested reinforced soils, the interface friction between geocell and gravel soil demonstrates the highest strength, indicating superior resistance to deformation. Conversely, clay reinforced by carbon fiber fabric exhibits the lowest interface friction strength, however, it displays a faster interaction with the soil with allowable minimal deformations. There is a significant difference in allowable deformations of different types of reinforced soils, which should be fully considered in practical engineering applications. A theoretical model for calculating interfacial friction resistance between non-cohesive soil and geocell reinforcement zone is proposed. The research findings can provide reference for the selection of reinforcement materials in reinforced soil engineering.

During precast beam yard construction on soft ground, prestress tensioning-induced camber transforms the initially uniform load distribution into eccentric concentrated loads at the beam ends, thereby posing risks to foundation stability and geometric accuracy. This study investigates the mechanical responses of natural ground, single-pile reinforcement, and double-pile reinforcement under tension loading through field monitoring and numerical simulations based on a Hangzhou–Ningbo Expressway project. The results show that single-pile reinforcement exhibits a typical point-support behavior, characterized by significant stress concentration at the pile head, a pile–soil stress ratio ranging from 3.0 to 4.0, and a coefficient of variation in base pressure reaching 0.81. In contrast, the double-pile scheme enables load redistribution through a line-support mechanism along the beam length, improving stress uniformity and reducing the coefficient of variation to 0.62. Orthogonal test-based sensitivity analysis further identifies pile diameter and cushion thickness as the dominant factors influencing composite ground. performance. This study clarifies the differences in load-transfer mechanisms among various pile arrangements under tension loading and provides a theoretical basis for the optimized design of casting bed foundations for precast beam yards in soft soil regions.

The improvement and reuse of completely weathered granite (CWG) with poor engineering properties for backfilling embankments can help protect the environment and bring great economic benefits. The embankment of high-speed railways demands an extremely low additional subgrade settlement under long-term dynamic loads. To analyze the applicability of the improved CWG used for subgrade filling, a series of laboratory dynamic triaxial and field cyclic loading tests were carried out. On the basis of the test results, a calculation model of accumulative plastic strain considering the dynamic stress ratio and the cement content was established. Using the proposed model and the numerically calculated dynamic stress, the accumulative plastic deformation of an embankment filled with improved CWG under various driving conditions was calculated and discussed. The variation of accumulative plastic deformation of the improved CWG with loading cycles could be described by a power function. The dynamic stress level had a significant influence on the accumulative plastic strain, and the strain in the bottom layer of the subgrade bed was greatly attenuated. Accordingly, most of the accumulative plastic deformation attenuation occurred within the depth range of the subgrade bed. The final total accumulative plastic deformations of the embankment were less than 2 mm (5 mm for the limit value) after 4 million times of high-speed train loadings, proving that the improved CWG can be used for subgrade filling. The influence of the axle load on accumulative plastic deformation was more significant than that of the train speed. The proposed calculation model of the accumulative plastic strain could provide valuable reference for similar railway engineering.