Analysis Of Thermal-hydro-mechanical Coupling Effectson Railway Subgrade In Seasonally Frozen Region

Frost damage of High-speed railway(HSR)is a widespreadphenomenon in seasonally frozen regions.In order to ensure traffic safety and comfort,it is urgent to solve the problem of frost heave.Frost heave deformation is a multi-physics coupling problem.It is of great practical significance to improve and perfectdesign,construction,operation and maintenance of HSR in seasonally frozen regions by fully analyzing the change processandcoupling mechanism of the water field,temperature field and deformation field of the subgrade.In this paper,the method of field monitoring,theoretical analysis and numerical simulation is used to analyze the thermal-hydro-mechanical coupling effect on the typical section of Harbin-Dalian HSR subgrade.The main achievements include the following parts:(1)Based on the classical hydrodynamic model and thermoelasticity basic theory,the multi-physics coupling mathematical model of moisture,temperature and stress is deduced.The relation equations of this modelare composed of soil-water characteristic curve,solid-liquid ratioand linear expansion coefficient.On this basis,the hydrothermal characteristic parameters of frozen and unfrozen soil are uniformly expressed by step function.(2)Based on the secondary development of COMSOL,classic freezing test inversion is carried out and the simulation results are compared with the data of indoor test.Research shows that the simulation results are consistent with the experimental results,the correctness of mathematical model is preliminary verified.In the process of freezing,moisture shift from positive temperature region to negative temperature region,and moisture field requires more time to reach a stable than temperature field.After the redistribution of moisture,the maximum change value of mass water content is 4.5%,accounted for 24% in the original moisture content,the migration behaviour of the moisture can’t be ingored.(3)Taking the typical section of Harbin-Dalian high-speed railway subgrade as an example,considering the effect of warm and cold slope,the coupling effect of water field,temperature field and deformation field of high-speed railway subgrade in seasonal frozen soil area is studied,and the numerical simulation results are compared with the field monitoring data.Considering the influence of climate warming,the initial temperature field and boundary condition of the model are determined based on the field monitoring data.The results show that the simulation results are in good agreement with the on-site monitoring data,and the model is reasonable.It can provide reference for the design,construction and later maintenance of subgrade.Due to the warm and cold slope effect,the temperature field of the subgrade are asymmetric in the transverse direction,and the maximum freezing depth of the right shoulder is the largest(1.8 m),the left shoulder comes second(1.6 m)and the center is the smallest(1.2 m).The water change of the center of subgrade mainly occurred in the depth of 2.5 m,the maximumchange value ofmass water content is2%,compared with the original water content increased by about 20%.There is uneven settlement(up to 14 mm)on the subgrade,the maximum vertical displacement of the right shoulder is 18 mm,the left side of the shoulder is 16 mmand the center of subgrade is 12 mm.