Reasonable excavation step footage and lining support timing are highly important for improving tunnel construction efficiency and ensuring construction safety. Taking the Huanxian No. 1 Tunnel of the Xi-Yin railway as the basis of this study, a 3D numerical model was established using MIDAS GTS NX290 finite element software. This model was used to investigate the deformation and force characteristics of the tunnel-surrounding rock and support structures under three different excavation footages and four different lining construction timings; the numerical results were then compared with the on-site monitoring results. This research aimed to determine reasonable excavation parameters for the three-bench seven-step excavation method used in shallowly buried loess tunnels. The results revealed positive correlations between the excavation step footage and surface subsidence, crown subsidence, and clearance convergence. An excavation footage of 3 m could balance construction efficiency and safety effectively. Keeping the secondary lining construction time unchanged, the early closure of the initial support was beneficial for reducing the force on the secondary lining. Keeping the early closure time of the initial support unchanged, the early construction of the secondary lining would lead to an increase in the force on the secondary lining. The initial support of the tunnel is recommended to be closed as early as possible, and the construction of the secondary lining should be shifted by 21 m behind the upper step palm surface. By comparing the on-site monitoring data with the numerical simulation results, similar trends were observed, providing reference and guidance for the subsequent construction of large-section tunnels in shallowly buried loess formations.

Influenced by factors such as the freeze–thaw cycle and water–salt migration, road construction in Uzbekistan’s highway project areas is prone to dissolution and subsidence, salt swelling, corrosion, and other engineering diseases. To investigate how various factors impact saline soils in Uzbekistan’s monsoon freezing zone, we conducted analyses of stress–strain curves, failure strength, and shear strength parameters of these soils through freeze–thaw (F-T) cycle tests and unconsolidated and undrained (UU) triaxial shear tests. The findings indicate that with the increase of salt content, the average reduction in the failure strength of saline soil was 15.8%, 6.3%, and 5.7%; with the increase of water content, the average reduction in cohesion was 10.8%, 44.1%, and 32.6%; and the internal friction angle increased with the increase of the number of F-T cycles and decreased with the increase of freezing temperature. Ultimately, we defined the rates of failure strength deterioration and cohesion damage in saline soil due to various factors, analyzing the destructive impacts of these factors. The results demonstrate a strong correlation between the curves of failure strength deterioration and cohesion damage ratios, indicating that the significant degradation of saline soil due to salt is primarily influenced by F-T cycles, with the extent of damage closely linked to water content.

Freeze-thaw (F-T) cycle tests and triaxial shear tests are conducted under varying freezing ambient temperatures and different F-T cycles for remolded loess. The results indicate that nearly all stress–strain curves of remolded loess exhibit strain-hardening behavior under varying freezing ambient temperatures and different F-T cycles. A decrease in freezing temperature alters the yield strain of loess and diminishes its resistance to deformation. As the freezing temperature decreases and the number of F-T cycles increases, the failure deviatoric stress of loess initially decreases, then increases, and eventually stabilizes. The most detrimental freezing temperature is −12 °C, which significantly exacerbates the adverse effects of F-T cycles on failure deviatoric stress. The strength indices initially decrease and then increase with decreasing freezing temperatures, while they first decrease and then stabilize with an increasing number of F-T cycles. Notably, the deterioration of cohesion is significantly greater than that of the internal friction angle. A quantitative analysis is conducted to examine the relationship between failure deviatoric stress, shear strength index, temperature, and freeze-thaw cycles. The fitting results effectively quantify the influence of different variables on the strength characteristics of loess. The findings of this research have significant theoretical implications for practical engineering applications in the northwest loess region.

To investigate the characteristics of water and salt migration (WSM) in saline soils subjected to climate conditions characterized by large temperature differences. In this paper, salted soil highway roadbeds in Uzbekistan were selected as the background for the study, and the salted soils in the region of the site were remodeled through a field study and based on field data. Subsequently, utilizing the assembled laboratory test apparatus, a model test of the WSM on the remodeled saline soil was carried out to analyze the behavior of the WSM in response to large temperature differences, the resulting soil deformation, and the influence of varying cold-end temperatures and alternating cooling and heating times on the WSM. The findings indicated that the temperature profile with in the soil column (SC) exhibits a “wavy” pattern as a result of thermal conductivity. During the freezing phase, water migrates from the lower section to the upper section in response to the temperature gradient and soil-water potential. Conversely, during the melting phase, water diffuses and migrates from the upper section downward in the form of steam molecules due to the action of evaporation. This process culminates in a “C” shape distribution of the curve of the water content inside the SC. During the freezing process, salt migrates from the bottom to the top along with the liquid water. Conversely, during the melting process, salt accumulates at the top of the SC accumulates. This phenomenon results in an “S” distribution of the salt content inside the SC. At the end of the freeze-thaw cycle (FTC), the deformation of the saline soil increased with the decrease of the cold end temperature, and the alternating time between heat and cold did not produce significant changes in the deformation of the saline soil. The moisture content at the upper end of the SC increases with decreasing cold-end temperature. The increase in the number of FTCs exacerbates the salinization of the soil in a certain part of the interior of the SC. The findings of this research may offer a theoretical foundation and technical assistance for the design of subgrade structures in saline soils subjected to climates characterized by large temperature differences.

A series of (45 sets) true triaxial shear tests with controlled suction and under conditions of equal-b and equal-p are performed on unsaturated compacted loess. By incorporating the effects of matric suction in unsaturated loess and the influence of middle principal stress conditions, the characteristics of the stress–strain curve evolution, strength failure line and related strength parameters of the unsaturated compacted loess under complex stress paths are analyzed, and the applicability of different strength criteria is analyzed. The results indicated that both the matric suction and the middle principal stress condition have significant effects on the magnitude of shear stress. While matric suction exerts minimal effect on the configuration of the stress–strain curve, the middle principal stress condition markedly affects its shape. A function is established to approximately describe the correlation between the strength-related parameters and the middle principal stress coefficient. A comparison of the failure lines predicted with several strength criteria and the experimental data indicates that the experimental results of unsaturated compacted loess under a controlled suction state are consistent with the results of the predicted failure lines of the Lade–Duncan strength criterion. The findings can provide crucial theoretical support for engineering design and disaster prevention in loess regions.