Abstract:Qinghai—Tibet railway crosses 550 km continuous permafrost regions and 82 km discontinuous permafrost regions,where high temperature regions(annual average ground temperature is above -1.0 ℃) occupy 275 km,ice-rich regions cover 221 km,overlapped sections of high temperature and ice-rich occupy about 134 km. As a result of the influences of both global climate warming and railway engineering on the permafrost degradation,design and construction of roadbed in permafrost regions are faced with quite great difficulties. As the natural thermal state and underground ice are the important factors influencing the roadbed stability,the choice of roadbed structure to protect permafrost is the leading principle of engineering design. Therefore,many measures are put forward and adopted including crushed rock slope protection,crushed rock embankment,embankment of heat pipe,embankment of awning,thermal-insulation treatment embankment,widened and heightened embankment and duct-ventilated embankment,etc. The crushed rock slope protection,crushed rock embankment,embankment of heat pipe,embankment of awning,and duct-ventilated embankment are all actively protective technologies. The embankment of crushed rock slope protection,crushed rock embankment and duct-ventilated embankment are chosen to study the protective effects of the three kinds of embankments on the permafrost based on the in-situ monitoring results of the roadbeds in Qinghai—Tibet railway. The basic data of actively adjusting and cooling roadbed measures in permafrost regions have been obtained and analyzed. Results show that all of the three measures have certain effects on adjusting and cooling roadbed,and are advantageous to protect permafrost under the roadbed. However,the rising of artificial permafrost table needs to consume the cold energy of soil below ground,which indicates that the temperature fields of permafrost foundation are in instable phase.