Study On Stability Of Railway Subgrade In Permafrost Regions Of Qinghai-Tibet Plateau

The construction of Railway Subgrade in permafrost regions destroys the heat balance between the original surface and the atmosphere,which changs the depth of permafrost melting layer beneath the railway subgrade.Field observations show that thermal absorption of the zero section and low embankment in the warm season increases significantly due to the shape change of subgrade surface.The artificial upper limit depth of permafrost is more than the sum of subgrade height and the upper limit of natural permafrost.Eventually,the upper limit of permafrost subgrade is gradually decreased.For the subgrade of height slightly higher and completion of the construction in summer,the freezing depth in permafrost area in winter is often greater than the melting depth in summer,which may make the roadbed in the winter period of freezing depth is more than the height of roadbed and natural permafrost table and the formation of cohesive frozen soil layer.But in the next year,the thaw depth of roadbed in the warm season is less than the sum of subgrade height and the upper limit of the natural permafrost.The upper limit of frozen soil below the subgrade began to rise,resulting in the formation of frozen soil cores.In view of the above problems,the main contents of this paper are as follows:1)Based on the numerical permafrost subgrade phase transition of two-dimensional unsteady temperature field analysis,and using the theory of grey correlation the influence factors on temperature field of roadbed in permafrost regions(the height of roadbed,slope and pavement width)were analyzed,and the critical height of embankment are studied;2)By establishing a two-dimensional phase change plate insulation subgrade non steady state temperature field model,the influence of laying position and the thickness of insulation board in the railway subgrade in permafrost regions to the temperature field are analyzed;3)Based on the analysis of the working mechanism of the thermal bar,the heat transfer model of the thermal bar is established.The temperature field of the two-dimensional unsteady subgrade is analyzed by using the finite difference method;4)By considering roadbed filling,engineering conditions,water,heat,salt,the relationship between engineering topography and other factors and mutual,AHP and fuzzy comprehensive evaluation method were applyed to establish a quantitative evaluation model,and the stability of railway roadbed in permafrost regions of Qinghai Tibet Plateau was evaluated.