Study On Frost Damage Analysis And Treatment Measures Of Subgrade And Culvert In Alpine And Cold Region Of High-speed Railway

Lanzhou –Xinjiang high-speed railway is the first high-speed railway located in the cold area of northwest China.Because of the special engineering geology,meteorological conditions and hydrological conditions,the subgrade and culvert of the line in Haomen-Daliang section are prone to frost heaving deformation,which affect the safe operation of the train and the passenger’s requirements for train comfort.Through field investigation,laboratory test and numerical simulation,the freezing damage situation and characteristics of subgrade and culvert in Haomen-Daliang section of Lanzhou –Xinjiang high-speed railway are analyzed in this paper.The causes of freezing damage and freezing damage treatment measures are studied,and the following conclusions are drawn:(1)Haomen-Daliang section of Lanzhou –Xinjiang high-speed railway is located in the south of Qilian Mountain,with high altitude alone the line,low temperature all the year round,abundant surface water,Subgrade in an alpine cold and humid environment.This section is extremely cold and long in winter,with a freezing period of nearly 6 months,and the soil freezing depth is more than 180 cm,which belongs to the deep seasonal frozen soil area.(2)The frost damage mainly concentrat in low embankment and replacement subgrade with zero height,followed by culverts and transition section,with the least cutting.The amount of frost heaving at the embankment is controlled at less than 5mm,and the amount of frost heave in the transition section is 5~10mm,and the freezing and expansion of the individual transition section is greater than 10 mm.The maximum frost heave occurs at culvert-roadbed transition section every year.The frost damage of culvert-roadbed transition section is serious.The number of frost damage during the three freezing periods from 2015 to 2018 in Haomen-Daliang section of Lanzhou –Xinjiang high-speed railway decreased year by year.The area in which the section is located is extremely cold and long in winter,and the fine particles of the bottom filler of subgrade is more,the water content and the frost heave rate are larger,which belongs to weak sensitivity ~ more sensitive heaving soil.The culvert-roadbed transition section is a multidirectional freezing state,which is easy to be introduced into the base bed soil in winter.Subgrade and culvert are prone to frost damage under the action of low temperature and water in winter.(3)The numerical simulation of the temperature field of a typical subgrade section shows that for subgrades with a subgrade height of 1 m,the maximum freezing depths at the center of the track,the center of the line,the shoulders and the foot of the slope are 2.7 m,2.61 m,3.08 m and 2.97 m,respectively.Due to the difference in thermophysical properties of the materials,the maximum freezing depth throughout the subgrade is greater than the freezing depth of the natural soil.The freezing depth at the center of the line and at the center of the track is less than the freezing depth at other locations on the roadbed,and the freezing and melting time is late.(4)According to the numerical simulation of temperature field of culvert,in cold season,the lowest temperature of culvert top filling is lower than that of culvert bottom filling.In warm season,the highest temperature of culvert top filling is higher than that of culvert bottom filling,the maximum frozen depth of culvert bottom is 2.71m;Compared with culvert bottom filling,the culvert top filling freezes early and melts early.The existence of culverts aggravates the freezing depth of the culvert transition section,in the cold season,the soil at the same depth below the subgrade,the closer the culvert is,the lower the temperature;the greater the freezing depth of roadbed-culvert transition section.The temperature field of the roadbed-culvert transition section of the connotation road 0-4m away from the culvert center is most affected by the culvert,followed by the range of 4-8m,and the least affected beyond 8m;And the maximum frozen depth of culvert transition section is 5.5m(1.7-2.5 times that of ordinary subgrade).(5)The anti-freeze measures of Lanzhou –Xinjiang High-speed Railway during the construction period are mainly carried out in terms of water prevention and drainage,filling control and heat preservation.In the later operation period,aimed at the causes of frost damage of subgrade and culvert in Haomen-Daliang section,measures such as sealing cracks,setting up seepage blind ditches on both sides of the line and adding a frost-resistant berm were adopted.According to the investigation,it is known that the subgrade of the seepage blind ditch section is added,and the effect of freezing damage is better except for individual sections.Suggestions on insulation measures for low embankments and culverts are put forward,from the numerical simulation number,it is known that the insulation layer is set at 40 cm,60cm and 80 cm under the subgrade surface,the insulation effect is obvious,and the second kind of heat preservation effect is the best.The thermal insulation material is laid on the inner wall of the culvert,and the freezing depth of the transition section of the culvert and the culvert is much smaller than that of the non-insulated culvert bottom and the freezing depth of the transition section,the freezing rate is decreased,and the heat preservation effect is remarkable.