A numerical simulation on the forecast of freezing-thawing processes surrounding a mountain tunnel

A numerical simulation on the forecast of freezing —thawing processes surrounding a mountain tunnel, 5. 5m in diameter,with an elevation of about 3800m,and a mean annual air temperature of near —3°C was conducted. An investigation showed that the tunnel will across an unfrozen bed rock in an alpine permafrost region. The preliminary forecast states a permafrost surrounding the tunnel concrete lining will form at first year after operating, and it would occur a frozen thickness of about 3. 0m three years later. Furthermore,an insulation layer is suggested for preventing the tunnel lining from frost damage,in which while the thickness of the insulation, 0. 022W/m. k in thermal conductivety coefficient, is nearby 10cm,the permafrost would not form after operating for more than thirty years.