Law of frost heave of canal foundation and appropriate thickness of insulation board under different groundwater levels

Abstract: In order to find out the difference of canal foundation frost heave in Hetao irrigation area under different underground water levels, and to understand the influence of the changes of groundwater level on soil moisture transfer and mechanical properties of canal foundation, the test was carried out by setting up a test platform for frost heave under different underground water levels. And combined with the prototype channel, the effect of different groundwater levels on frost heave of foundation soil covered with different thickness of polystyrene board was analyzed, the distribution law of frost heave rate and section bending moment along channel slope was described, and a theoretical formula for calculating the suitable thickness of polystyrene board at different underground water levels was presented. It is found that the frost heaving of base soil decreases by 0.15 cm when the groundwater level is reduced by 1 cm. When the groundwater level is reduced by 0.5-1.0 m, the frost heave rate is reduced by 71%-83.8%. The decline of groundwater level effectively prevents or delays the increase of capillary water in soil, reduces the soil moisture of 0-30 cm soil layer, effectively prevents the migration of the water of freezing front, reduces the formation of ice interlayer in soil, and reduces the frost heaving deformation of soil. The frost heaving damage parts of the channel change with the change of the groundwater level. Through the analysis of ground temperature monitoring data, this paper puts forward the lowest temperature under the condition of laying 2-10 cm polystyrene board, fits the relation between the thickness of insulation board and the lowest temperature under the board at different underground water levels, and calculates the laying thickness of polystyrene board under different groundwater levels when the negative temperature does not exist under the board, so as to explore a relation between the suitable thickness for polystyrene board laying and groundwater depth. According to the theoretical formula, the variation rule of soil frost heave rate along the slope is proposed. When the groundwater level is lower than the bottom of the canal, the maximum frost heave of canal foundation soil is located at the foot of the slope of the canal, and the frost heave rate along the slope decreases gradually. When the groundwater level is higher than the bottom of the canal, the maximum frost heave of the slope is located at the 1/3 of the lower part of the slope, and the maximum frost heave of the slope is gradually transferred upward with the decrease of groundwater depth. When the groundwater depth is relatively shallow, the channel’s maximum frost heave is located at the middle part of the channel slope. The soil water content in 0-50 cm soil depth decreases under the 2 conditions of actual decrease of groundwater level and ground elevation. And the migration amount increases with the depth. Migration rate difference is 1.75%-4.46%. The results show that the soil water transport has the consistent change rule whether the ground is raised or the groundwater level drops. This study can provide scientific basis and technical support for the research of thermal insulation and anti-expansion technology in the northern seasonal frozen soil area.