Forecast analysis for the re-frozen of Feng Huoshan permafrost tunnel on Qing-Zang railway

According to the in-situ measured data of the air temperature and ground temperature inside of Feng Huoshan Tunnel on Qing-Zang railway, China, the thawed range of the permafrost surrounding the tunnel is very large, which is caused by the hydration heat of the cast-in-situ concrete lining, insulation measurement during winter construction and other artificial activities. In this paper, taking the coupled effects of moisture transfer and heat conduction into account, the finite element formulae of this problem with phase change are derived from the governing differential equations and moisture transfer equations using Galerkin's method and the software for computers is edited. Using the software, forecast analysis for the re-frozen of Feng Huoshan permafrost Tunnel is made. The analysis results indicate that the vault, left wall and right wall of Feng Huoshan Tunnel without the thermal insulation material will be refrozen on 30 September 2004, and the arch bottom will be refrozen on 30 September 2005. However, if the tunnel is fitted with the thermal insulation material whose thermal conductivity is 0.0186(W/m K), the vault of the tunnel will be refrozen on 30 September 2005, and the left wall, the right wall and the arch bottom will be refrozen on 30 September 2006. If thermal conductivity of the thermal insulation material is 0.03(W/m K), the vault of the tunnel will be refrozen on 30 September 2004, and the left wall, the right wall and the arch bottom will be refrozen on 30 September 2005. So, the thermal insulation material will prevent the thawed range of Feng Huoshan permafrost tunnel from being refrozen. The thawed range of the permafrost surrounding the cold region tunnel caused by construction must be taken into account in design and the time of the field observation should be extended, or observational results, such as their temperature and stress field, will greatly be different from results in stability.