Thermal-mechanical properties of polystyrene insulation board under defect condition and their influence on lining structure of conveyance channel

The seasonal frozen soil area in the north of China has a low temperature in winter, and laying an insulation board is an effective method for mitigating the frost-heaving damage to the lining structure of the conveyance channel. However, the insulation board has a certain defect rate during installation and later operation, which changes its thermodynamic and mechanical properties, thus affecting the safety of the lining structure. In this study, an expanded polystyrene insulation board was adopted and its thermal-mechanical properties were examined under the condition of defects. Then, the effect of the insulation board with defects on the lining structure was analyzed by conducting numerical simulations, taking a conveyance channel of a Jiaodong water diversion project as an example. The experimental results showed that with the increase in freeze–thaw times and decrease in defect size, the moisture content and thermal conductivity of the insulation board with defects increased. After 28 freeze–thaw cycles, compared with the complete insulation board, the moisture content and thermal conductivity of the insulation board with 20-mm defect decreased by 21.63% and 4.33%, respectively. With the increase in freeze–thaw times and defect size, the elastic modulus and compressive strength of the insulation board with defects decreased. After 45 freeze–thaw cycles, compared with the complete insulation board, the elastic modulus and compressive strength of the insulation board with 20-mm defect decreased by 17.76% and 6.67%, respectively. The numerical simulation results showed that when air media existed in the defects, the deformation and stress change of lining were not distinctive. When ice media were present in the defects, the larger the defect size, the larger the freezing depth of the channel, the larger the normal frost-heaving displacement of the lining surface, the greater the possibility of tensile damage of the lining inside, and the more significant the outward expansion trend of the canal slope lining. In the middle of a shady slope, compared with the complete insulation board, the average freezing depth of the insulation board with 20-mm ice defect increased by 2.29 times, the maximum normal frost-heaving displacement increased by 4.50 times, and the normal frost-heaving stress and tangential freezing stress increased by 16.86 and 7.47 times, respectively. These results can provide a theoretical reference for the safe and efficient operation of water diversion projects in dry and cold regions.