Study On The Roadbed Structure Of Anti-frost Heave Of High-speed Railway Subgrade In Deep Seasonally Frozen Region

Traffic infrastructure in deep season frozen soil region develops rapidly in China.Seasonal frost heaving is the main technical obstacle to the construction of high-speed railway subgrade.Research on suitable anti-frost heaving subgrade structure is Significant for the sustainable development and safe operation of high-speed railway in deep season frozen soil region.Based on the China Railway Corporation's Science and Technology Research and Development Plan(2014G003-F)?the National Natural Science Foundation projects(51178281,51208320),by means of in-situ monitoring,laboratory test and numerical simulation,combined with experience and theoretical analysis methods,the evolution law of subgrade frost heaving deformation in deep season frozen soil region and effective measures for frost heaving prevention and control are summarized.The laboratory tests on the engineering properties of the heat preservation strengthening layer material and the surface layer of the subgrade bed are carried out.The thermal insulation effect of different structures is verified by finite element method.The feasible anti-frost heaving subgrade structure is put forward,the interlaminar mechanical properties of anti-frost heaving subgrade are calculated.and on this basis,the engineering performance and quality control index of heat preservation strengthening layer material and anti-frost heave filler on the surface of subgrade are studied;The optimum structure form of antifrost heaving subgrade is put forward.The research results can provide technical reference for the selection of anti-frost heaving subgrade structure of high-speed railway in deep season frozen soil region.The main achievements are as follows:(1)Based on the analysis of the monitoring data of ground temperature and deformation during the construction period of Haqi high-speed railway subgrade section,it is considered that the frost heave of Haqi high-speed railway subgrade can be divided into five stages: initial frost heave stage,rapid frost heave stage,frost heave stability stage,maximum frost heave stage and thaw settlement retreat stage with time.(2)Based on the test data analysis of laboratory tests of foam concrete,such as physical,mechanical and engineering properties,etc.The results show that the foam concrete mixed with basalt fiber can not only meet the strength requirements of the high railway base,but also has better thermal insulation performance,which is the preferred material for the thermal insulation layer of the high-speed railway subgrade in the deep seasonal frozen soil region.(3)Based on the laboratory tests of strength,deformation and freeze-thaw durability of cement-stabilized macadam,it is suggested that cement-stabilized macadam with particle size less than 0.25 mm and 3% ?5% cement should be selected as frost heave resistance of the surface layer of high-speed railway subgrade bed filler in deep seasonal frozen soil area.Compressive resilience modulus and unconfined compressive strength can be used to rapidly and comprehensively evaluate the compaction quality of the surface layer of subgrade,the surface layer of the subgrade bed with good strength,stiffness,frost heave resistance and permeability is formed.(4)Based on the Harbin high speed railway subgrade section parameters and in-situ monitoring,a thermo mechanical coupled simulation analysis model of subgrade structure under the rail foundation is established.On the basis of verifying the reliability of the model,the insulation effect of the frost heaving subgrsde bed is calculated,and the freezing depth of the fiber foam concrete can be reduced by 39%?50%.The frost heave deformation of subgrade is reduced by 16%?42% by filling with Cement Stabilized Macadam on the surface of the subgrade.Therefore,the fiber foam concrete heat preservation strengthening layer and cement stabilized macadam bed surface has good frost heaving properties.(5)The thermal mechanical coupling model of the subgrade structure under train load is established.Based on the calculation of the stress between the structural layers,the applicability and service performance of the filler are discussed.It is concluded that fiber foam concrete and cement stabilized macadam can be used as the heat preservation strengthening layer and the surface of the subgrade respectively,and the deformation of the subgrade and the stress between the layers are coordinated.The stiffness of subgrade surface,subgrade bottom and subgrade are 220 MPa/m,160 MPa/m and 120 MPa/m respectively.Cement stabilized macadam subgrade surface is the key to determine the service life of subgrade.It is suggested that the thickness of the subgrade should be 60 cm,and with 10 cm thick heat preservation strengthening layer,2/3 of the freezing depth can be ensured to occur in the surface area of subgrade.At the same time,it meets the requirements of the design and service life of the main subgrade engineering.