Test for frost heaving damage mechanism of rigid-soften composite trapezoidal canal in seasonally frozen ground region

In the area of seasonal frozen soil in North China and Northwest, there exists massive and serious frost-heave damage of concrete lining canal. Frost-heave damage is the main reason for the channels. In this paper, the prototype experiments were conducted in order to explore the frost-heave mechanism of rigid-soften composite canal in the irrigation area of high-cold region. The frost deformation the soil moisture variation of the trapezoidal canal lined with concrete and composite geo-membrane, and especially the rules of frost-heave deformation and the deformation features of composite geo-membrane were further systematically studied. The experiment followed the leading thought of suiting and reducing the frost-heave destruction, chose the trapezoidal canal lined with infiltrating structure and integrated rigidity materials as typical experiment segment, and collected the freeze index of various canal lining frameworks; the experiment referred to the advanced method, and adopted the new material. The experiment section of observation prototype was 50 meters long. The measuring section for ground temperature was 3 meters long, and the temperature was measured by the digital thermometer. The measuring section for freeze depth was 3 meters long, measured by the DTM-2 frozen soil apparatus. The section for frost-heave stress was 4 meters long, measured by the strain sensor. The section for frost deformation was 5 meters long, measured by the electronic level and the electronic theodolite. The section for foundation moisture was 20 meters long, and the foundation moisture was measured by the drying method. Prototype test data were obtained through the observation every day. The observation objects in the test included air temperature, ground temperature, foundation moisture, freeze depth, frost deformation and frost-heave stress. The frost-heave mechanism of trapezoidal canal lined with concrete and composite geo-membrane was studied in the prototype experiment, as well as the soil moisture movement on canal base during seasonal freezing-thawing stage. The variation law of frozen depth and frost-heave deformation was derived from soil moisture movement, freezing temperature and frost depth. Based on the observed data in the prototype experiment of the trapezoidal canal lined with concrete and composite geo-membrane under the condition of freezing-thawing cycle, the ground temperature change, the rules of frost-heave deformation and the distribution of normal and tangential frost-heave force were analyzed. The results showed that, the frost-heave amount had a maximum value of 13.1 and 11.2 cm respectively at the site of one third from the bottom on shady slope and at the bottom of trapezoidal canal, which caused lining structure of the canal to rise. During the freezing period, the soil moisture content in the depth of 0-60 cm increased with the increasing of the depth, while that in 60-120 cm decreased with increasing of the depth. The maximum value of water migration and variation was 13.2%, which occurred in the bottom of the canal. After one freeze-thaw cycle, the strength and deformation quantity of composite geo-membrane were still maintained above 90%, so it could fully utilize the features of frost-heave resistance and adaptive deformation of composite geo-membrane. The study shows that the prototype experiment of the canal can provide the reference and the scientific basis for the engineering design of the lining canal with concrete and composite geo-membrane and the mechanics computation in seasonal frost region.