灌淤冻土复合衬砌渠道保温防冻胀效果分析

为解决河套灌区渠道混凝土衬砌冻胀破坏问题,该研究提出由聚氨酯和聚苯乙烯2种材料组成的复合衬砌结构,建立渠道基土水热力耦合数值模型,通过现场试验和数值模拟方法分析不同衬砌结构下基土地温、含水率、冻胀量及等效应力变化。结果表明:与无保温衬砌结构相比,阴坡聚苯乙烯复合衬砌结构和聚氨酯复合衬砌结构下基土最低地温分别提高67.1%和64.7%,最大迁移含水率分别减少8%和9%,最大冻胀量分别减少80%和81%,基土内等效应力明显减小。这2种复合衬砌结构具有保温效果好、冻胀变形小等优点,可作为寒区渠道保温防冻胀衬砌结构的选择。同时数值模型计算结果与试验值基本吻合,说明此数值模型可合理地描述渠道基土冻结过程中地温和冻胀量变化。研究可为寒区渠道防冻胀衬砌结构设计提供理论依据和参考。

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.