The unreasonable setting of thermal insulation layer in high cold tunnels not only increases the maintenance cost of tunnels, but also weakens the anti-freezing and cold resistance of the tunnels. In order to optimize the setting of thermal insulation layer in an Alpine tunnel, relying on Dabanshan tunnel in Qinghai Province, three schemes of radial and longitudinal thermal insulation region of thermal insulation layer were adopted, and the temperature field of the surrounding rock was numerically analyzed. The results show that the uneven region scheme of 9 cm-8 cm-7 cm and 10 cm-9 cm-8 cm insulation layer can effectively reduce the freezing area of the lining and the surrounding rock, the freezing region at the tunnel entrance is significantly reduced, and there is no lining freezing region within the depth of 30–750 M. The research results can provide guidance for the partition wall setting of radial and longitudinal insulation layers of Alpine tunnels. In addition, it has considerable economic advantages for the reduction in engineering construction costs.

The deformation control effect of loess tunnel composite foundation plays an important role in optimization design and reinforcement effect evaluation. Systematically evaluate the adaptability of the composite foundation of jet grouting pile in shallow collapsible loess tunnel. Taking the shallow buried section of Fujiyao Tunnel with a buried depth of 20 m as an example, using MIDAS finite element numerical simulation software, the foundation deformation control during construction and settlement control after construction are systematically studied, the differential deformation control is analyzed, and the reinforcement effect of the tunnel bottom is evaluated. The results show that the uplift displacement can be controlled by changing the pile length and increasing the replacement ratio. The combination of long and short piles can significantly reduce the uneven settlement and plastic zone of the foundation. The uneven settlement of 9 mm can be used as the evaluation index of the composite foundation reinforcement effect in a shallow buried section of the loess tunnel.

Due to the complexity of the surrounding rock structure and the geological environment of tunnel excavations, traditional analytical methods are insufficient in effectively dealing with the complex nonlinear deformation problems arising from tunnel excavation. In contrast, geomechanical model tests can comprehensively simulate the excavation construction process of tunnels and the mode and time effects of loads, providing a more realistic reflection of the complete process of engineering stress and deformation. Therefore, this study conducted a model test on reinforcing the loess tunnel base, building upon the first tunnel of the Lanqing Expressway located on the north bank of the Yellow River in Lanzhou City. The study utilized similarity theory to explore the theoretical design of the model and established a specialized model test platform to design the experiments with the goal of obtaining more scientific and effective experimental schemes to ensure the safety of soil reinforcement in tunnel bases during construction. This research will contribute to improving the safety, reliability, and economy of loess tunnel base reinforcement projects, and has a certain reference value for research in this field.

Based on the G85 high-fill subgrade project in east Gansu Province, this study conducts one-dimensional compression tests in the laboratory on both disturbed and in situ-compacted loess. Through the combination of the test results of remolded soil, compaction standards for each layer of the subgrade fill are established, and quality inspections of the compacted subgrade are performed. The experimental results demonstrate that the compression deformation of remolded loess exhibits a positive correlation with compaction degree and a negative correlation with moisture content. Under constant compaction degree conditions, axial pressure and deformation follow a linear relationship, whereas under fixed conditions, the relationship adheres to a quadratic trend. Specimen void ratios show minimal variation within the 25–100 kPa stress range but undergo significant reduction between 100 and 400 kPa. Under an axial compressive load of 100–200 kPa, the compression coefficient at a height of 10 m within the subgrade ranges from 0.163 to 0.171 MPa⁻¹. At a height of 6 m, it ranges from 0.177 to 0.183 MPa⁻¹, and at 1 m, from 0.183 to 0.186 MPa⁻¹. These values indicate that the compaction quality throughout the subgrade corresponds to a low compressibility level. However, the compaction quality near the slopes on both sides is slightly lower than that along the centerline of the subgrade. Overall, the compaction quality meets the required standards.