This paper investigates the frost heave and thaw settlement characteristics of the pipe–soil system during the freeze–thaw cycle, along with the underlying mechanisms. A numerical simulation platform for the complex pipe–soil system was developed using the heat conduction equation, moisture migration equation, and stress–strain equation, all of which account for the ice–water phase change process. The simulations were performed with the coefficient-type partial differential equation (PDE) module in COMSOL Multiphysics. By employing coupled thermal–hydraulic–mechanical (THM) simulation methods, the study analyzed the changes in volumetric water content, volumetric ice content, moisture migration patterns, and temperature field distribution of a water pipeline after three years of service under real engineering conditions in the cold region of northern Xinjiang, China. The study also examined the effects of parameters such as pipeline burial depth, specific heat capacity, thermal conductivity, permeability of saturated soil, and initial saturation on the displacement field. The results show that selecting soil layers with high specific heat capacity (e.g., 1.68 kJ/kg·°C) and materials with high thermal conductivity (e.g., 2.25 W/m·°C) can reduce surface frost heave displacement by up to 40.8% compared to low-conductivity conditions. The maximum freezing depth near the pipeline is limited to 0.87 m due to the thermal buffering effect of water flow. This research provides a scientific reference and theoretical foundation for the design of frost heave resistance in water pipelines in seasonally frozen regions.

Coal mining has generated a large amount of underground space, which has traditionally been reused mostly as mine wastewater storage. Given the excellent thermal insulation properties of these mine reservoirs, their potential for seasonal energy storage is considerable. However, research on cross-seasonal thermal energy storage utilizing coal mine underground reservoirs remains limited, and the thermal storage characteristics of such systems throughout their entire operational cycle are not yet fully understood. This study employs numerical simulation methods to analyze the thermal storage performance of a cross-seasonal thermal storage system based on a coal mine underground reservoir throughout a fully operation cycle. Based on the actual geological conditions of the Daliuta Coal Mine in the Shendong Mining Area, we established a thermal-fluid coupling model for a coal mine underground reservoir. Using this model, we analyzed the entire process of the heat injection stage, heat storage stage, and heat production stage within the cross-seasonal thermal energy storage system. Based on the model, the feasibility of utilizing a coal mine underground reservoir for cross-seasonal thermal energy storage was evaluated, and the system’s thermal storage performance was assessed. Results indicate that under current geological conditions of the Daliuta Coal Mine and designed operating parameters, the effective heat storage rate of the cross-seasonal system can reach 78.16%. Through investigation of the thermal storage process, the distribution evolution of hot water and heat dissipation mechanisms were thoroughly analyzed. This study identified the heat storage phase as the primary stage controlling heat loss and discussed key influencing factors affecting the thermal storage process. These findings provide novel insights for utilizing coal mine goafs and residual underground spaces, offering a reference for developing and designing novel energy storage facilities.

The development of coal resources has created a large number of underground mined-out spaces, which can be utilized for cross-seasonal thermal storage through underground reservoirs to achieve seasonal heat storage. However, there is currently limited research on the cross-seasonal thermal storage capabilities and thermal storage performance evaluation of coal mine underground reservoirs. This study aims to evaluate the operational stability and long-term performance of a Coal Mine Underground Reservoir Energy Storage System (CMUR-ESS) under realistic geological conditions of the Shendong Coalfield. A multi-physics coupling model, integrating thermal-fluid processes, was developed based on the actual structure of the No. 5-2 coal seam goaf in the Dalinta Mine. Numerical simulations were conducted over five annual cycles, each comprising injection, storage, production, and transition stages. Results demonstrate that the system achieves progressive thermal accumulation, with the volume fraction of water above 70 °C increasing from 75.0% in the first cycle to 88.9% by the fifth cycle at the end of the storage stage. Production temperatures also improved, with peak and final temperatures rising by 6.2% and 6.8%, respectively, after five cycles. The analysis confirms enhanced heat retention and reduced thermal loss over time, indicating robust long-term stability and sustainability of the CMUR-ESS for seasonal energy storage applications. The results of this study can provide a reference for the design and evaluation of CMUR-ESS.