Effects of thermal insulation and anti-frost heaving in composite lining structures for a canal in colmatage frozen soil

This study aims to explore the frost heaving failure of concrete lining in a canal in the Hetao Irrigation Area. Two composite lining structures were proposed, including polyurethane and polystyrene. A coupled heat-moisture-stress model was established for the channel soil. In-situ test and numerical simulation were combined to analyze the variation in soil temperature, moisture content, frost-heave capacity, and equivalent stress in different lining structures. The results showed that: The ground temperatures were -8.5 ℃ and -2 ℃ at the normal depth of 16 cm on the shady slope and sunny slope of non-thermal insulation lining structure; those were -2.8 ℃ and -1.5 ℃ at the same positions for the polystyrene composite lining structure; those were -3.0 ℃ and -1.4 ℃ for the polyurethane composite lining structure. The maximum water contents were approximately 13% and 4% at the normal depth of 20 cm on the shady slope and the sunny slope of non-thermal insulation lining structure before and after freezing; those were 5% and 2% at the same location for the polystyrene composite lining structure; those were roughly 4% and 1.1% for the polyurethane composite lining structure. The measured maximum normal capacity of frost heave were 14 cm and 4.7 cm on the shady slope and the sunny slope in the non-thermal insulation lining structure; those were 2.8 cm and 2.1 cm for the polystyrene composite lining structure; and those were 2.6 cm and 1.5 cm for the polyurethane composite lining structure. It infers that the maximum normal capacities of frost heave for the non-thermal insulation lining structure were far greater than those of the polystyrene and the polyurethane composite lining structure. The maximum normal capacities of frost heave were reduced by 80% and 81% on the shady slopes for the polystyrene and the polyurethane composite lining structure. The equivalent stress of channel soil for the non-thermal insulation lining structure was significantly greater than those of polystyrene and the polyurethane composite lining structure. This change can be attributed to the large difference in soil temperature for the non-thermal insulation lining structure, which can result in a large strain and stress of frost heaving in the canal soil. The stress concentration occurred at the inflection points of the top and bottom of a canal. The simulated values in numerical models were basically consistent with the experimental values, indicating that the mathematical model can be suitable to describe the changes of ground temperature and frost-heave capacity during the freezing process of channel soil. Two kinds of thermal insulation lining structures demonstrated the low permeability, low heat transfer, good function of heat preservation, and small deformation of frost heave. They can be excellent choices for seepage prevention and anti-frost heave of canal in seasonal frozen soil areas. The finding can be helpful to understand the frost heaving mechanism of channel soil, and further to provide a sound reference for the design and maintenance of channels in cold regions.