road works;  permafrost;  heat shields;  roadbed temperature field;  Buried deep;  Finite elements

The enthalpy model was used to establish the temperature field of frozen soil subgrade with phase transition. The influence of subgrade height, subgrade construction season and other factors on the optimal burial depth of the insulated board was comprehensively analyzed by considering the short-term and long-term permafrost protection effects, and considering the short-term and long-term permafrost protection effects. The finite element calculation showed that when the construction season was delayed to the cold season by 3 months, the frozen soil protection effect of the insulation board was significantly enhanced, and no melt core appeared in the roadbed within 20 years of operation. When determining the best burial depth of the heat insulation board, it is necessary to comprehensively consider the influence of the construction season, the height of the roadbed and other factors, if the roadbed is low, it should be shallow burial, the height of the roadbed is high, the warm season construction should be buried in the middle, and the cold season construction should be shallowly buried.