Enhancing Frost Heave Resistance of Channel Sediment Hetao Irrigation District via Octadecyltrichlorosilane Modification and a Hydro-Thermo-Mechanical Coupled Model

To address frost heave in winter-lined canals and sediment accumulation in the Hetao Irrigation District of Inner Mongolia Autonomous Region, while reducing long-term maintenance costs of canal linings and relocating sediment as solid waste, this study proposes the use of low-toxicity, environmentally friendly octadecyltrichlorosilane (OTS) to modify channel sediment. This approach aims to improve the frost heave resistance of canal sediment and investigate optimal modification conditions and their impact on frost heave phenomena, aligning with sustainable development goals of low energy consumption and economic efficiency. Water Droplet Penetration Time (WDPT) tests and unidirectional freezing experiments were conducted to analyze frost heave magnitude, temperature distribution, and moisture variation in modified sediment. A coupled thermal–hydraulic–mechanical (THM) model established using COMSOL Multiphysics 6.2 software was employed for numerical simulations. Experimental results demonstrate that the hydrophobicity of channel sediment increases with higher OTS concentrations. The optimal modification effect is achieved at 50 °C with a silane-to-sediment mass ratio of 0.001, aligning with the economic efficiency of sustainable development. The unidirectional freezing test results indicate that compared to the 0% modified sediment content, the 40% modified sediment proportion reduces frost heave magnitude by 71.3% and decreases water accumulation at the freezing front by 21.1%. The comparison between numerical simulation results and experimental data demonstrates that the model can accurately simulate the frost heave behavior of modified sediment, with the error margin maintained within 15%. In conclusion, OTS-modified channel sediment demonstrates significant advantages in enhancing frost heave resistance while aligning with the economic and environmental sustainability requirements. Furthermore, the coupled thermal–hydraulic–mechanical (THM) model provides a reliable tool to guide sustainable infrastructure development for hydraulic engineering in the cold and arid regions of Inner Mongolia, effectively reducing long-term maintenance energy consumption.