Optimal design of thermal insulation layer of a tunnel in permafrost regions based on coupled heat-water simulation

Abstract

In permafrost regions, if thermal insulation layer is thinner, seasonal freeze-thaw action can induce severe damages on a tunnel structure; otherwise, the construction cost is high and not economical. To find out a scientific balance between the safety and the economy of the tunnel in permafrost regions, an optimal design on the thermal insulation layer should be carried out according to some relevant numerical or analytical calculations. To solve this problem, a coupled heat-water model for the tunnel in cold regions is built on the basis of energy and mass conservation principles. Then a representative permafrost tunnel in the Qinghai-Tibet Plateau (QTP) is used as an example to simulate temperature and water processes of the surrounding permafrost, and thereby a key position and an unfavorable time are picked out for the optimal design. Subsequently, the optimal thickness of the thermal insulation layer for the permafrost tunnel is determined by a series of coupled heat-water simulations. Eventually, the temperature and water states of the surrounding permafrost of the tunnel at the unfavorable time are fully evaluated to make sure that the tunnel is free of freeze-thaw damages. This study is expected to better understand the coupled temperature and water processes in the surrounding permafrost of the tunnel and further design a safe and economical tunnel structure. Of course, it can serve as a reference for further investigation, too.