Preliminary study on cooling effect mechanisms of Qinghai-Tibet railway embankment with open crushed-stone side slope in permafrost regions

The embankment with open crushed-stone side slope (EOCSSS) in permafrost regions is an effective measure to cool subgrade and protect permafrost along the Qinghai-Tibet railway. According to the air temperature condition and geological condition at Beiluhe Test Base on the Qinghai-Tibet Plateau, the numerical analyses for the temperature field, velocity field and heat flow of the EOCSSS at Beiluhe Test Base along Qinghai-Tibet railway were conducted both during daily period and annual period to study the mechanisms of the cooling effect of the EOCSSS in the present paper. The results show: (1) The EOCSSS has cooling effect during summer nighttime, which is different from the traditional views; (2) The open crushed-stone side slope has “heat shield” effect due to the solar shading during warm months and the EOCSSS releases more heat during cold months than that absorbed during warm months according to the results of the heat flow computed, which is beneficial for protecting permafrost beneath railway embankment and keeping thermal stability of the railway embankment; (3) The major type of heat transfer of crushed-stone side slope is the forced convection according to the velocity characteristics showed; (4) The main mechanisms of the cooling effect of the EOCSSS are the “heat shield” effect due to the solar shading of the crushed-stone side slope and the heat flow difference, which results from the velocity difference of the pore air in the open crushed-stone side slope during daily period and annual period.