Experimental Study On Transitional Section Of New Type Of Road And Bridge In Permafrost Regions

Since the construction of the Qinghai-Tibet Railway,there have been a lot of disease problems in the transitional section of the permafrost zone,and the most serious of which is the difference settlement between the abutment and the transitional section.At present,for the problem of subgrade disease in permafrost region,there are permafrost roadbeds such as block stone roadbed and ventilation pipe subgrade and so on.The main cooling mechanism is to change the roadbed temperature and lift the upper limit of permafrost.heat.However,there is no unified transitional structure for the disease of road and bridge transition in permafrost region.The usual treatment measures are: backfilling with ballast or gravel in the sag caused by differential settlement.This approach has the advantages of high speed of repair,low repair cost and no effect on normal train operation.,But in the long run,this treatment to repair the high frequency,repair and maintain a short time,and easily lead to new disease problems.Therefore,it is necessary to propose a new type of transition structure between road and bridge in order to reduce the temperature of the disease and improve the quality of railway operation.Therefore,in this paper,through the combination of the roadbed disease prevention and control measures in the frozen soil area and the disease control measures in the transitional section of the general non-frozen soil,the structure of the transition zone of the new permafrost region is proposed,the results show that the water field,temperature field,settlement law and the effect of the transition section of the road and bridge are compared with those of the traditional crushed stone roadbed.The following conclusions are drawn:(1)The average temperature under the structural foundation of the new road and bridge transition section is lower than that under the traditional block gravel roadbed structure,which indicates that the new type of road and bridge transition section has better cooling effect on the foundation,and the block gravel layer temperature of the new road and bridge transition section Which is lower than that of the traditional block gravel roadbed.It shows that the gravel layer in the new transition zone has a strong natural convective heat transfer process.(2)The temperature,freezing-thawing cycle and loading of the subgrade have a great influence on the content of unfrozen water in the frozen soil layer.With the decrease of the temperature,the content of the unfrozen water decreases with the loading,Content increased,with the freeze-thaw cycle to increase the non-frozen water content reduction.(3)In the new type of road and bridge transition section,the settlement difference between road and bridge is much smaller than that of traditional block gravel roadbed structure,which shows that the structure of road and bridge transition zone in new permafrost region has a good effect on alleviating the differential settlement of road and bridge transition section.(4)Through the numerical simulation,the temperature field of the three types transition section is analyzed and it is found that it has better cooling effect.In its 50-year long-term thermal stability analysis,it is found that the long-term thermal stability of the new transition section is good.