Abstract:
Insulation board is a widely used canal insulation material in the northern part of China. Its thickness is usually determined by experience or by thermal calculations based on the total-insulation method. A canal, as a long line project, normally requires a huge amount of insulation boards. Subtle differences in laying thickness have a great influence on the project budget. Three main considerations include: 1) the thawing settlement reduction ability of the canal lining structure allows certain frost heave displacement; 2) frost heaving is bidirectional, which will cause compression deformation of soil under the freezing front; 3) insulation board may postpone the frost period of the canal foundation soil and weaken the freezing strength through delaying the freezing front and affecting moisture migration. Therefore, a partial-insulation method is reasonable and feasible. A saturated layer underlying the insulation board may develop using the partial-insulation method during the freeze-thaw season, which may cause canal stability problems. So the applicable conditions of the partial insulation method are presented, including the safe slope ratio, setting toothed walls, or a rigid bottom under the canal slope. A concrete trapezoidal canal is not suitable for the partial insulation method. Insulation board, using both the total insulation method and the partial insulation method, was designed and compared with the actual laying thickness in the west main canal of Chepaizi in Xinjiang of China. The results indicate that the project cost associated with the partial insulation method is reduced by 19%. The general-purposes finite element software ANSYS was applied to simulate the thermal-mechanical coupling process before and after the insulation board was laid. When actual mechanical parameters were not available for the concrete lining structure and frozen soil under different temperatures, this paper adopted general parameters that are widely used in other articles. After the thermal-mechanical coupling simulations were conducted, the equivalent linear expansion rates of frozen soil were obtained by inverse computation of measured frost heaving. Finally, the equivalent linear expansion rates were used to simulate the canal thermal-mechanical coupling process before and after insulation board was placed, and the frost heaving, frost-heave forces, and uneven frost heaving coefficient were extracted. The uneven frost heaving coefficient was defined as the quantity difference of frost heaving between two points dividing the distance. Numerical analysis indicates that the maximum amount of frost heaving of laid insulation board canal is 1.35 cm less than the allowable value (2 cm), which proves that the partial insulation method is safe and feasible. Meanwhile, the frost heaving quantities and frost-heave forces of the lining structure are not only apparently reduced, but also more uniform. Moreover, the reduction in the shady slope is 80%, and the uneven frost-heaving index of the canal base dropped 94%.