Abstract
This paper presents a simple practical equation for estimating the thickness of heat insulator between the inner and outer linings which is most widely used in road tunnels. To this end, using a one-dimensional tunnel-ground model, a non-steady periodic state under the condition of sinusoidal variation of air temperature in tunnel is analyzed on the basis of the thermal analysis. By using the equation presented, we can reasonably determine the optimum material of heat insulator and its optimum thickness. In addition, the equation is useful for a better understanding of the thermal characteristics of the tunnel-ground system.
