In order to study the changes in the mechanical properties of road subgrade in cold areas after the freezing and thawing of highways in cold areas, indoor mechanical tests were carried out to investigate the effects of the number of freeze–thaw cycles, freezing temperature, water content, and circumferential pressure on the mechanical properties of road subgrade soil in cold areas after thawing. The mechanical properties of road subgrade soil in cold areas after thawing were measured under different conditions. The test results show that, within the study range: (1) After 7 freeze–thaw cycles, the destructive stress of the subgrade soil decreased from 321.7 kPa to 289.9 kPa, a decrease of 9.9%, and the elastic modulus decayed by 19.9%. (2) When the freezing temperature was reduced from −5 °C to −15 °C, the destructive stress of the subgrade soil decreased from 303.9 kPa to 290.1 kPa, a decrease of 13.8 kPa, approximately 4.5%, and the decrease in modulus of elasticity was about 1.6%. (3) The water content increased from 6% to 12%, and the destructive stress decreased from 405.43 kPa to 288.4 kPa, a decrease of 29.1%, and the modulus of elasticity decreased approximately linearly, with an attenuation of 50.4%. (4) The peripheral pressure increased from 50 kPa to 150 kPa, and the destructive stress increased from 194.7 kPa to 367.7 kPa, a growth of 88.8%, and its modulus of elasticity increased with the increase in peripheral pressure, an increase of 154.1%. The results of this research can provide a reference for highway and engineering construction in the western silt–soil distribution area.

The uniaxial compression tests were conducted on granite samples with different joint dip angles to more favorably explore the influences of the nonconsecutive joint on mechanical properties and deformation characteristics of the rock mass. The stress‐strain curves, deformation and strength characteristics, and energy evolution process of the samples were analyzed. Numerical simulation using particle flow code (PFC) is employed to study the crack propagation process. The mode of jointed and fractured rock was investigated. The research results showed a significant reduction in both the peak strength and elastic modulus of jointed samples compared with intact ones: the peak strength and elastic modulus drop to the minimum at the joint dip angle of about 45°, especially for the peak strength, which takes up about 55% of the intact samples. The fractured samples’ total energy, elastic strain energy, and dissipated energy during the uniaxial compression drop significantly relative to intact samples. The proportion of the fracture modes varies with different joint dip angles, in which the ratio of shear cracks grows at first and then declines, with the highest balance at the dip angle of 45°. The damage stress’s sensitivity to the dip angle change is greater than that of the peak stress, with reduction amplitude more extensive than the latter.

This study aimed to enhance the slurry performance and durability of coal gangue-based geopolymers (CGGP) by incorporating four types of nanomaterials: nano-SiO₂ (NS), graphene oxide (GO) nanosheets, nano-CaCo₃ (NC), and nano-Al₂O₃ (NA). The microstructure and underlying mechanisms were thoroughly investigated using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results indicate that the type and dosage of nanomaterials significantly influence the rheological properties, strength development, setting time, porosity, and water absorption of CGGP. Specifically, the addition of GO nanosheets drastically reduced fluidity, with a 73.33% decrease in flowability compared to the control group at a 2.0 wt.% dosage. Nano-SiO₂ exhibited the most pronounced effect in improving compressive strength and shortening the setting time, with the optimal accelerating effect observed at a 1.5 wt.% dosage. Nano-CaCO₃ primarily acts as a filler. Though its reactivity is relatively low, at an appropriate dosage (1.5 wt.%), it can effectively reduce porosity and water absorption. Moreover, at a dosage of 1 wt.%, it exhibits the optimal 28-day compressive strength, which is 54.18% higher than that of the blank group. Nano-Al₂O₃ demonstrated a relatively stable accelerating effect on setting and yielded the best pore structure and strength at a 1.5 wt.% dosage. SEM analysis revealed that the incorporation of an appropriate amount of NC particles significantly improved the microstructural densification of the polymer. Concurrently, EDS results confirmed the positive influence of the nano-Al₂O₃ material on the distribution of hydration products and the interfacial structure. This research provides an important theoretical basis and technical support for the high-performance design and widespread engineering application of coal gangue-based geopolymers.

With the continuous expansion of urban rail transit networks, construction safety of connecting passages—as critical weak links in underground structural systems—has become pivotal for project success. Although artificial ground freezing technology effectively addresses adverse geological conditions (e.g., high permeability and weak self-stability), it is influenced by multi-field coupling effects (temperature, stress, and seepage fields), which may trigger chain risks such as freezing pipe fractures and frozen curtain leakage during construction. This study deconstructed the freezing method workflow (‘drilling pipe-laying → active freezing → channel excavation → structural support’) and established a hierarchical evaluation index system incorporating geological characteristics, technological parameters, and environmental impacts by considering sandy soil phase-change features and hydro-thermal coupling effects. For weight calculation, the Analytic Hierarchy Process (AHP) was innovatively applied to balance subjective-objective assignment deviations, revealing that the excavation support stage (weight: 52.94%) and thawing-grouting stage (31.48%) most significantly influenced overall risk. Subsequently, a Bayesian network-based risk assessment model was constructed, with prior probabilities updated in real-time using construction monitoring data. Results indicated an overall construction risk probability of 46.3%, with the excavation stage exhibiting the highest sensitivity index (3.97%), identifying it as the core risk control link. These findings provide a quantitative basis for dynamically identifying construction risks and optimizing mitigation measures, offering substantial practical value for enhancing safety in subway connecting passage construction within water-rich sandy strata.