The Hetao irrigation area of Inner Mongolia has the characteristics of a temperate continental arid and semi-arid climate zone, where the winters tend to be long and cold, resulting in seasonal frozen soil. In regard to the freezing and thawing processes of the foundation soil, the freezing usually occurs in mid-October, and the thawing in late May of the following year, forming a freezing-thawing cycle. The channel foundation soil is considered to be strong frost heave soil, which is dominated by loam and silty loam. Due to the influences of the fluctuations in temperature, characteristics of the soil, groundwater levels, and other factors, combined with the negative temperature effects, the Hetao irrigation area has become an area with strong frost heaving. Also, due to the negative temperature effects, and under the conditions of no anti-frost heaving protective measures in the concrete board-line channels, after several alternately repeated freezing-thawing cycles, the lined channels and anti-seepage engineering measures which exist in the irrigation area have been damaged to varying degrees. Furthermore, all of the channels show serious frost heaving damages. On the concrete faces of the channel linings, major damage phenomena have occurred, such as overhead and uplift movements with local collapsing. Each year after the freezing and thawing cycle, substantial amounts of manpower and funds are required for maintenance and reconstruction processes, which not only increases the difficulties and expense rate of the engineering management maintenance, but also affects the channel’s anti-seepage effects and service life.
The use of laid EPS under-lining bodies for anti-frost heave measures has been successfully applied in countries such as Japan and Canada. Also, massive experimental research applications have been conducted in Beijing, Hebei, Shandong, Inner Mongolia, Ningxia, Heilongjiang, and other regions of China. According to the experiences of Canadian engineering departments [
1], the laying of 1 cm thick EPS has the insulation effects equivalent to soil layers with 14 cm thicknesses. Furthermore, EPS measuring 6 cm in thickness can reduce the frozen depth by 50% or more [
2]. Guo [
3] used ANSYS software to analyze the change laws of the temperature, stress, and displacement fields under different thicknesses of EPS laid in the channel of the Hetao irrigation area of Inner Mongolia. Li [
4] carried out EPS channel anti-seepage testing in Xinjiang. The results indicated that when EPS was used for heat preservation in the channels with higher underground water tables, the uplift pressures were large, which was prone to destroy the lining layers. In the channel conducted experiments performed by Liu et al. [
5], it was proposed that 1 cm thick EPS could effectively improve the shady-slope ground temperatures of channel bases by 1.2 °C, and the sunny-slope ground temperatures by 0.7 °C. Song and He et al. [
6] established a corresponding insulation board thickness calculation formula using the theory of heat conduction and a thermal resistance equivalent principle. Then, using the calculation formula, they proposed an optimal structural pattern for the insulation and anti-frost heave effects of concrete-lined channels. Li et al. [
7] concluded that a simple and practical related analogy method and equivalent thickness method could be used to analyze the calculation methods of the insulation board thicknesses in different regions. The acquired test data from the Hebei Section in the middle route of the South-North Water Transfer were used for verification and correction purposes. However, the possibility that reserved frozen soil existed was not considered, which would potentially lead to high cost expenditures. Guo and Wang et al. [
8] used ABAQUS finite element software to simulate the change rule of the anti-frost heaving force for EPS lined channels, and proposed the flexible utilization of EPS. Meanwhile, in the cases of frost heave effects in the channels, it was found that insulation boards had certain buffer and stress release effects, which tended to lead to more even stress distributions in the lined channels. Zhang [
9] discussed the advantages of C20 precast concrete slabs and the EPS lined channel for the Shuangta main channel from the three aspects of economy, technology, and anti-frost heave effects.
In the research of anti-frost heave mechanisms conducted by Everett [
10], the first frost-heave capillary theory was proposed. However, the proposed capillary theory was unable to explain how discontinuous ice lenses were formed. Also, this theory underestimated the frost heave pressure in fine-grained soil. Therefore, based on the aforementioned first frost heave theory, Miller [
11] proposed a second frost heave theory to overcome the deficiencies of the capillary theory. In this second theory, it was believed that an ice margin with a low moisture content, low moisture conductivity, and no frost heave effects existed at the freezing front and the warmest ice lens bottom, which provided the basis for the establishment of a numerical model. Harlan [
12] proposed a water-thermal coupled hydrodynamic model, and utilized a finite difference method for simulating the water flow and temperatures in the soil. This was found to be only suitable for one-dimensional moisture migration, and no calculation method for the soil water potential had yet been presented. Wang et al. [
13] proposed the change rules of water, heat, and displacement during the process of channel frost heave through the establishment of a channel model. Liu et al. [
5] theoretically analyzed the insulation mechanism of benzene boards and calculated their economic application benefits in channel anti-frost heave situations. From the perspective of mechanics, Jiang and Tian [
14] proposed that the overall upward lifting movements of firm-to-soft hybrid channel lined structures were mainly due to the interactions between the upward frost heave deformations of the bottom linings of the channels, and the radial deformations of the slope plates. Wu and Wang et al. [
15] discussed the application effects of EPS in the concrete-lined channel of the Ningxia Yellow River irrigation area. Li [
16] performed mechanical testing on the concrete channels of active mold bags in large irrigation areas in order to analyze the change characteristics of the stress and strain in those areas. Zhang [
17] used a finite element method for the numerical simulation of the trapezoidal channel of the Xinjiang Corps, with consideration given to the fact that the channel failure characteristics were dominated by a crack formed at the 1/4 to 1/3 part of the channel bottom along the channel line, and that the channel base presented an uplift phenomenon under uneven frost heave conditions. Liu and Wang et al. [
18] applied Automatic Dynamic Incremental Nonlinear Analysis (ADINA) software to create a model of a lined channel with an “adaptive variable cross-section”. The study results showed that the channel with an “adaptive variable cross-section” reduced the maximum normal frost heave quantity by 55.11%; the maximum normal frost heaving force by 51.65%; and the maximum tangential freezing force by 56.85%. Li and Fei et al. [
19] analyzed the U-shaped channel anti-frost heave mechanism by using a thin shell structure theory. It was considered that the main reasons for the U-shaped channel damage were the negative influences of soil moisture in the channel base and the adverse weather conditions, which resulted in destructive uneven frost heave conditions in the channel. Hao et al. [
20] proposed that the optimal insulation board thickness for the Hamatong irrigation area in Heilongjiang was 10 cm, and that 12 cm was the ideal thickness for the channel bottom. It was determined that when the optimal slope coefficient of the trapezoid channel was 2, the project costs were relatively low. Liao and Liu et al. [
21] presented a new type of integrated anti-seepage insulation composite structure with a strong anti-seepage and anti-scouring ability, along with remarkable insulation and anti-frost heaving effects, a reasonable structure, good stability, and reliable operation. However, the construction of the proposed structure was more complicated. Zhu [
22] believed that the plastic flow could only occur when the stress was greater than the long-term strength, and the total strain rate was decomposed into attenuation creep strain and non-attenuation creep strain rates. Then, by considering this theory, a constitutive model could be established which was suitable for the static load reaction temperature effects. Shen Mu et al. [
23] proposed three field-coupling problems of water, temperature, and stress fields, and presented a simple coupling model. Shen et al. [
24] considered that the uneven frost heaving of lining boards due to shear and foundation soil was the main factor related to frost heaving damages in trapezoidal channels with concrete precast slab linings. The restrictions on the sizes of the lining boards have led to very small internal stresses on the boards. Therefore, fracture damages generally do not occur. Song and Yu et al. [
25] presented applications of SBS modified asphalt waterproof coiled material, along with APP modified asphalt waterproof coiled material, in channel lining projects in order to improve the stability and strength of the channels. However, the construction costs were found to be higher than those of other methods. Wang [
26] conducted prototype observational experiments during the frost heaving processes of trapezoidal cast-in-site concrete channels with arc slope angles. Then, using the statistics of the test field temperatures, foundation-based soil moisture content, and channel observation point displacements, the frozen depths, rigid lining layer deformations, and stress change factors of the channel bed were analyzed. Zhang and He et al. [
27] established a standardized structure for channel anti-seepage, insulation, and anti-frost heaving, and determined their application conditions and scopes. Also, they summarized an empirical method for the insulation board thicknesses, and a calculation method based on a thermal resistance equivalent principle, in order to propose the technical requirements for laying the insulation boards, and the control standards for the quality inspections. An, Xing et al. [
28] used theoretical calculation methods to analyze the change rules of the tangential frost heave forces and normal frost heave forces. The results of their experimental testing indicated that the tangential frost heave forces were relatively axisymmetric to the center of the channel bottom, of which the numerical sizes showed approximate symmetrical distributions along the cross-sections. Due to the buffering actions of the benzene boards, the tangential frost heave forces became greatly decreased, in which the shady-slope forces were observed to have been cut by 92.7%. In regard to the normal frost heave forces with the laid EPS, it was found that at other parts of the channel, the forces were cut by more than 80%, and those at the bottom of the channel were reduced by 94%. Zhang and Wang et al. [
29] established a channel frost heave mechanics model which they combined with a finite element model. They then used an isotropic calculation to show that local normal frost heave forces existed in the upper shady-slope with a maximum value of 0.063 MPa. Meanwhile, the forces in the sunny-slope were very small, and mainly distributed in the upper part with a maximum value of 0.04 MPa. Liu and Ning et al. [
30] believed that there was a relationship between the soil-ice elastic constants and those of the entire frozen soil mass at a certain temperature. On this basis, a damage mechanics method was applied in the research studies of the frozen soil mechanics in order to establish a frozen soil constitutive model which considered the soil mass damages.
At the present time, there have been numerous research studies completed regarding the frost heave mechanism of EPS lined channels. However, testing results regarding insulation effects and mechanisms, as well as suitable laying thicknesses, are still lacking. Meanwhile, there is no relevant research on the suitable EPS thickness, frost expansion mechanism, and water transport law under certain conditions in the Hetao area. At present, no heat preservation scheme for channels exists that is applicable to the Hetao area, and the problem of channel frost heaving has not been solved. Thus, in this study, the frost heaving amounts, frozen depths, ground temperatures, and ground water levels of EPS with different thicknesses were monitored. The anti-frost heave mechanisms of insulation boards laid under the conditions of precast slabs were also analyzed. Meanwhile, the suitable laying thicknesses of the EPS boards under precast concrete linings were discussed for the Hetao irrigation area, so as to put forward the heat preservation scheme of the channel under certain conditions in the Hetao area, analyze the main causes of frost heaving, and solve the regional frost heaving problem under certain conditions. The results of this study provided a scientific basis, demonstrations, and technical support for the future applications of EPS insulation boards with anti-seepage linings in the main channels of the Hetao irrigation area.