Numerical Simulation of Frost Heave and Thaw Settlement Characteristics in a Complex Pipe-Soil System in the Seasonally Frozen Ground  
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[PERSON]  
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[PERSON]  
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3 School of Civil Engineering and Architecture, Northeast Electric Power University, Jilin 132000, China; 3 eic0612@com. 1  
[PERSON]  
4 Jilin Zhongcheng Municipal Engineering Co., Ltd., Jilin 132000, China; 3 [EMAIL_ADDRESS] (P.  
or rupture [11]. The axial stress in the pipeline caused by frost heave can be approximated using the bending stress analysis method for beams [12]. By combining the classical fluid dynamics model with basic thermoelastic theory and using soil-water characteristic curves and the solid-liquid ratio as basic equations, the frost heave mechanism in high-speed railway subgrades can be effectively analyzed [13]. The study results show that subgrade deformation is significantly affected by changes in air temperature and humidity distribution. Thus, controlling the thermal-water migration characteristics in the subgrade is an effective way to reduce frost heave deformation and uneven deformation. The Drucker-Prager elastoplastic model [14] can be used to simulate pipeline damage caused by frost heave at high-pressure regulating stations in river areas. By installing heaters to increase the intake temperature, frost heave in natural gas pipelines can be effectively prevented. [PERSON] et al. [15] proposed a numerical model based on isogeometric analysis (IGA) to simulate the thermo-hydro-mechanical (THM) coupling process during ground freezing. In addition, the phenomenon of thaw settlement should not be overlooked. As the temperature increases, frozen regions gradually thaw, causing significant changes in the physical properties of the soil, which leads to a decrease in its bearing capacity. During thaw settlement, the heterogeneity and anisotropy of the soil also significantly influence the mechanical behavior of the pipeline. This heterogeneity can be quantified by factors such as the soil's layered structure, particle composition, and moisture content. For example, clayey soils and sandy soils respond differently to changes in moisture content; the former may exhibit greater compressibility and settlement after thawing. Additionally, the thaw settlement process is accompanied by changes in the soil's internal friction angle and cohesion, which further affect the stability of the pipeline. [PERSON] et al. [16] investigated fault slips caused by permafrost thawing, as well as the longitudinal strain resulting from changes in fluid temperature and soil permeability during thawing. Thermal siphon pipes [17; 18] can be used to study the effects of hydrothermal coupling on the soil temperature field in frozen ground. In engineering practice, researchers often simplify coupling models based on specific conditions and apply efficient algorithms to solve them, taking into account specific boundary conditions and initial states. During the freeze-thaw cycle, the mechanical behavior of frozen ground exhibits complex nonlinear characteristics. [PERSON] et al. [19] studied two key factors affecting the overall vertical displacement of pipelines: frost heave caused by the leading frost layer and settlement due to thawing within the thawing ball and moisture migration. The low permeability of the leading frost layer can form a water flow barrier, inhibiting pore water pressure generated during thawing. In practical engineering, for silty clay and silt, appropriate measures can be taken based on moisture content, while for sandy soils and certain silts, adjustments can be made based on clay content to effectively prevent frost heave and thaw settlement [20]. Other frost-related mechanisms include slope instability, river ice scour, and pipeline buoyancy. Recent advances in pipeline integrity research highlight critical strategies for addressing frost-related challenges. Ref.