Study on hydrothermal coupling and frost heave characteristics of trapezoidal concrete-lined canals with gradient sand-gravel replacement in cold regions

This research focuses on the problem of frost heave damage in trapezoidal concrete-lined canals in cold regions. Using the main canal of the Jingdian Irrigation District, China, as the engineering prototype, the control effect of the thickness of the sand-gravel replacement layer on the temperature field, moisture field, and frost heave deformation of the canal foundation was systematically analyzed through a combination of prototype monitoring experiments and numerical simulation. The optimal sand-gravel replacement thickness suitable for trapezoidal concrete-lined canals in cold regions is proposed. The results indicate that the sand-gravel cushion layer significantly inhibits water migration and frost heave development during the freezing process of the foundation soil by blocking the capillary water migration path and regulating the heat conduction characteristics. Increasing the replacement thickness can effectively delay the advancement rate of the freezing front, significantly reducing the frost heave deformation, normal frost heave force, and tangential freezing force of the canal, resulting in a more uniform distribution. With a gradient replacement scheme ranging from 30 cm at the top to 70 cm at the bottom of the canal, the peak normal frost heave force and tangential freezing force were reduced by 40.3% and 38.7%, respectively, and the maximum normal displacement decreased from 4.26 cm of the original foundation soil to 0.95 cm, meeting the specification requirements of 0.5 to 1.0 cm, thereby achieving the frost-heave mitigation goal in a cost-effective manner. The results provide a theoretical basis for the design and application of sand-gravel replacement canal foundations in cold regions.