Abstract
In this study, a field temperature test was performed to reveal the insulation effect of the thermal insulation layer installed at lining surface. The thermal insulation layer is made of polyphenolic, and the thickness is 7 cm. According to the test results, the temperature of the thermal insulation layer and lining continuously changes with the air temperature in the tunnel in an approximately trigonometric function. The temperature of tunnel lining without thermal insulation layer is close to the air temperature, which results in the lining frost in winter. The maximum temperature difference between the two sides of the thermal insulation layer can be 27°C. In the section whose buried depth is more than 11.4 m, the temperature of lining with thermal insulation layer in winter is mainly influenced by the cold air in the tunnel. When the monthly mean and lowest daily mean air temperature are lower than −10°C and −14.3°C in the coldest month, the temperature at the inner side of the thermal insulation layer is below 0°C. When the buried depth is less than 11.4 m, the temperature of lining is also influenced by the low temperature at ground surface. The temperature of lining is lower. The thicker thermal insulation layer and even active heat measure are needed. Therefore, the design of thermal insulation layer thickness should consider the air temperature distribution and tunnel buried depth along the tunnel length.
Highlights
To date, numerous cold region tunnels have been built in North Europe, North America, Japan, and China
Under the e ect of the air ow outside the tunnel, the air temperature in di erent monitoring sections along the length of the tunnel changes with the ambient air temperature outside the tunnel, whose overall change rules are similar and in an approximately trigonometric function. e air temperature in January is lowest in the whole year. e temperature values of the air, reproof layer surface, and outer surface of the thermal insulation layer are close in the sections with the thermal insulation layer, and the temperature change rules are coincident
The heat transfer occurs in the thermal insulation layer, which makes the temperature at the inner side of the thermal insulation layer continuously change with the air temperature
Summary
Numerous cold region tunnels have been built in North Europe, North America, Japan, and China. E lowest ambient air temperature outside the tunnel could be − 28°C. e calculation results show that the 6 cm-thick polyphenolic insulation layer whose thermal conductivity is 0.025 W/(m·k) can prevent the tunnel lining and surrounding rock from freezing-thawing damage. E air temperature load in the tunnel in winter was selected as − 20°C. e results show that the temperature of tunnel lining is close to 0°C in winter, when the thermal insulation layer whose thickness and thermal conductivity are 5 cm and 0.02 W/(m·k), respectively, is installed at the lining surface. According to the field temperature measurement results in the Tianhengshan tunnel in China, Luo found that the temperature at the waterproof board between the secondary and primary linings was still below 0°C in winter, a 5 cm-thick thermal insulation layer made of polyurethane was installed at the lining surface [27]. A comprehensive temperature measurement was conducted along the length of the Zuomutai tunnel in the Hegang-Dalian highway (G11) in China. e temperature change rules of air, thermal insulation layer, and lining in the tunnel were investigated. e actual insulation effect of the thermal insulation layer was analyzed on the basis of the temperature changes of the thermal insulation layer and lining under different air temperature loads in different monitoring sections. e results can provide references for thermal insulation layer thickness design in seasonally frozen region tunnels
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