Study On Mechanical Properties Of Ballartless Track Ac-reinforced Subgarde Bed Of High-speed Railway In Seasonal Frozen Areas

With the massive construction of ballastless track high speed railway in the world,higher requirements have been put forward for the structural safety,stability and durability of its high-speed operation.Especially for the seasonal frozen soil area,the durability and stability of the subgrade structure under extremely low temperature is highlighted in many high-speed railway.The frost heaving and shrinkage cracking of the subgrade in the seasonal frozen soil region,including Harbin to Dalian high-speed railway,has seriously affected the comfort and safety of the high speed railway operation.With the continuous development of China's high-speed railway construction to the international market,combining with the environmental background of Moscow to Kazan high-speed railway construction project in Russia,this paper puts forward a new base bed structure of the full section asphalt concrete strengthening surface.According to the plan,the Moscow to Kazan high speed railway will be 770 km long,across the Eurasian continent and through the 7 federal bodies in Russia,covering more than 25 million people.The minimum temperature in the region is below-45 C,and the highest temperature in summer is above 20degrees C.The whole course is planned to set up 15 stations,and the maximum design speed is400 km.The cold weather for half a year and the serious permafrost problems are all obstacles in the implementation of the high speed rail project.The conventional foundation bed structure of high speed railway subgrade can not meet the requirements of waterproofing,anti freeze and durability in seasonal frozen soil areas.Therefore,it is necessary to study the actual situation of the seasonal frozen soil area in Russia's high speed railway,and put forward a suitable form of subgrade foundation bed structure for high speed railway.Asphalt concrete has excellent performance in waterproofing,frost prevention and durability.As road surface and airport pavement material,asphalt concrete's structural behavior and damage model are relatively thorough,and the methods of calculation and test are relatively rich.However,for the construction of a new type of high speed railway subgrade structure with asphalt concrete,on the one hand,the impact of the load form,the structure layer and the environmental factors are obviously different from the traditional asphalt pavement and the asphalt airport pavement.On the other hand,the service life of the asphalt pavement is generally within 15 years,and the structure of the railway subgrade requires more than 100 years of service life.It is not conclusive about whether the construction of the asphalt concrete foundation bed structure can reach the service life,and there is no theoretical model and engineering experience for various diseases and damage modes that may occur in the AC reinforced subgrade.It is not clear how the anti freeze crack,bearing capacity and long term service durability in practical application are not clear,so it also restricts the popularization and application of the new structure of asphalt concrete in the construction of high speed railway in some degree.The purpose of this study is to focus on the load mode,frost resistance and durability related properties under load.The large dynamic model test is carried out in the laboratory to verify the deformation characteristics and long-term stability of the asphalt concrete full section reinforced base bed under cyclic loading,and to discuss a series of problems applied to the foundation bed structure of the high speed railway subgrade.In the overall structure of the Ballastless Track Subgrade of high speed railway,the mechanical characteristics and service performance of the substructure(the surface of the base bed,the bottom of the base bed,etc.)have been greatly changed after introducing the reinforced surface of the asphalt concrete,and the methods and the standard methods used in the traditional structural form in the stress analysis and the design of the structural thickness will have an effect.Therefore,based on the cumulative plastic deformation state of the base bed packing,the asphalt concrete bed structure is optimized,the stress analysis of the whole subgrade structure and the design method of the thickness of the structure layer will be put forward.The main achievements of this paper are as follows:(1)The temperature field of the base bed is simulated by the finite element model.The temperature stress of the base bed is simulated based on the temperature temperature field.The factors that affect the temperature stress of the asphalt concrete layer are analyzed,and the design requirements and the frost resistance limit are put forward.(2)The research on the fatigue limit of asphalt concrete at home and abroad is analyzed.The maximum local control strain of the bottom layer of the long life design of the high speed railway asphalt concrete is 50??.In the seasonal frozen soil area,considering the influence of freeze-thaw cycles,the cumulative fatigue damage M_A<0.5 must be satisfied.(3)The asphalt concrete strengthening layer can effectively improve the distribution of dynamic stress in the base bed.Based on the cumulative deformation time effect state control method,the parameters of the foundation bed structure are optimized.The thickness of the ballastless track bed layer is reduced and the cost of the engineering is reduced.(4)Based on the principle of"vertical foot scale,load matching,temperature simulation",a large dynamic model test of asphalt concrete reinforced foundation bed is carried out.The results show that the concrete strengthening layer can effectively reduce the impact of cyclic loading on the base bed structure,reduce the cyclic deformation of the base bed and greatly enhance the deformation of the base bed.Stability.The accumulated plastic deformation stability values did not exceed the elastic deformation under the corresponding temperature environment,showing good temperature adaptability and resistance to permanent deformation.