Research On Frost Heave Characteristics Of High-speed Railway Subgrade In Seasonally Frozen Soil Area

In recent years,the construction of China’s high-speed railway has developed rapidly.The Lanzhou-Xin Jiang high-speed railway which is the longest high-speed railway in the world was completed in 2014,has connected Lanzhou and Xin Jiang.It’s also the important part of AsiaEurope railway.The opening and operation of Lanzhou-Xin Jiang high-speed railway has formed a railway transport network in the western of China with wider coverage,greatly facilitating the movement of the population and promoting the economic development in northwest of China.Although the construction technology of high-speed railway in China has been matured,there are still some technical difficulties in the operation process,especially in the permafrost region of the Qinghai-Tibet Plateau,where the environment is harsh and the geographical conditions are complex.Therefore,further research is needed in combination with the actual situation of the roadbed frost heave.This paper based on the high fill embankment section from Menyuan to Haomen section of Lanzhou-Xin Jiang high-speed railway.Through field investigation,theoretical analysis,experimental study and numerical simulation,etc.,the characteristics and laws of the frost heaving of subgrade were studied.The contents included frost heave observation for two years,frost heave characteristic test of roadbed filler,temperature field,seepage field and deformation field of subgrade.The main research contents are as follows:(1)Combined with the climatic and environmental conditions in Menyuan,the frost heaving mechanism and the factors affecting the development of the Lanzhou-Xinjiang Highspeed railway was analyzed.Based on the long-term field observation of subgrade frost heaving deformation of(K1934 + 969 ～ K1935 + 969)the section of Lanzhou-Xinjiang high-speed railway from Menyuan to Haomen in winter,the monitoring results were systematically analyzed.And the development law of subgrade frost heaving deformation with the change of temperature was summarized and analyzed in combination.(2)Selected the typical subgrade filling to carry out the conventional soil test.from where the frost heave is more serious.The non-uniformity coefficient and coefficient of curvature of subgrade filling were measured by sieving analysis method.The water content of subgrade soil was measured by drying method.The optimum moisture content and the maximum dry density were determined by moisture-density test.(3)Combined with the results of subgrade soil conventional soil test,the corresponding frost heave test was carried out.Firstly,the change of the temperature field inside the subgrade filling specimen and the change of the frost heave amount of the sample during freezing process which was under the action of temperature gradient have been studied.Secondly,the water migration of soil column samples with different water content after freezing was analyzed.Finally,analysed the specimen’s variation law of frost heave deformation after several freezethaw cycles which compaction degree was 90%.(4)First of all,analysed the theory of frozen soil temperature field,moisture field and strain field coupling mode.And then using the finite element analysis software Comsol to simulate the frozen soil roadbeds’ water-hot-force three coupling numerical simulation.Analyzed the changing rule of temperature field over time and the subgrade moisture migration along with the degree of freezing and the changing regulation of the frost heave of frozen process.(5)Summarized the current use of the frost heave treatment measures and effects.Combined with the settlement observation of the study,through the frost heave test and numerical simulation analysis of research results,the research and development of subgrade slope waterproof equipment,discharge of heat insulation and roadbed subgrade humidity.Using the new measures can effectively prevent the subgrade frost heave.