Study On Reasons And Treatments Of Subgrade Frost Damage In The High Latitude Section In Lanzhou-Xinjiang High-speed Railway

Lanzhou-Xinjiang High-speed Railway is the first large-scale high-speed railway in China to cross the northwest loess plateau(Lanzhou-Xining),alpine areas(Xining to Zhangye),gobi sand storm area(Hexi Corridor,Gobi area of Xinjiang);Haomen to Daliang interval in high altitude,cold and damp areas,the winter climate is cold and lasts for a long period of time,since the end of October to the end of April in the following year,up to six months in the winter period,it is easy to cause roadbed frost damage,resulting in a large amount of maintenance work,affecting the normal operation of the train.This article takes the section of the Haomen-Daliang section of the Lanzhou-Xinjiang High Speed Railway as an example.The frost damage of the subgrade of high speed railway in the cold region of the western China is studied.Through the investigation and analysis of the subgrade in the cold-damaged section,the cause of the frost damage was analyzed,and the cold-damage prevention and control measures are implemented to ensure the normal operation of the line and provide reference for similar railway construction in the area.Through the investigation and analysis of the frost damage situation of the subgrade of the Lanzhou-Xinjiang high-speed railway,indoor and field tests,numerical simulations and on-site monitoring,the following conclusions have been drawn::(1)Haomen-Daliang interval of Lanzhou-Xinjiang high-speed railway in high altitude area in which the temperature is relatively low and the amount of rainfall(snow)is large;the freezing time is long and the maximum depth of soil freezing is above 183 cm in the winter.The subgrade is in an extremely cold and humid environment all year round.Most of subgrade frost damage happens in embankment section,the frost damage section is mainly the low embankment and replacement subgrade with zero section,and the chilling damage in the culvert transition is more prominent..(2)The bottom of roadbed was compacted with B class filler,in which the content of particle size less than 0.075 mm is 3.76% ~ 21.46%.These filler will produce frost heave resulting in subgrade frost damage under appropriate moisture and temperature.(3)As the subgrad where frost damage occurs is mostly low embankment,zero-cross section burying roadbed,shallow road boring and culvert transition,most of the difficulties in the prevention and drainage of water,it is affected by rainfall and melting snow.Water infiltrates the roadbed,culverts and the transitions on both sides of the road,from the roadbed surface,slopes,culverts,and foundations,etc.,resulting in the high moisture content in the subgrade,which causes the subgrade to freeze and swell under the effect of negative temperature in winter.(4)In open and closed conditions,the frost-swelling test of coarse particles containing fine particles is carried out.Under the condition of closed system,the frost heave ratioincreases with the increase of moisture content and fine particle content,and the fine particle content is 3.76% ~ 21.46%,and the frost heave ratio of the filler is up to 1.1% ~ 2.2% in saturated state.The frost heave ratio under open system is much higher than that under closed system,and the frost heave ratio is 3.65% ~ 4.72% when the compacting factor is 0.93.(5)Numerical simulation analysis of subgrade temperature field of a typical cross section of the road from the area of Haomen to Daliang.In mid-April,the subgrade reached the maximum depth of freezing.The natural ground surface,slope foot,5.2m from the centerline of the line,and the centerline of the track were 2.3m,2.89 m,3.09 m,and 3.3m,respectively.The frozen depth at the track centerline is the largest;the numerical calculation results are basically consistent with the measured results.(6)Due to the subgrade using traffic,driving without too much impact,in order to adopted in treatment of subgrade frost damage to establish water seepage blind ditch,adding high wall insulation duct,repair all kinds of cracks and other measures.6 section of subgrade frost heaving measured data analysis in Haomen to Daliang interval shows that the number of subgrade frost damage,line limitation are greatly reduced,and the uneven frost heave amount is reduced,the subgrade frost heave quantity control in the following 4 mm,more high speed railway line maintenance workload is greatly reduced.