Research On Frost Heave Characteristics Of Pile-slab Structure Roadbed In Frozen Area

To build high-speed railways in seasonal frozen soil areas,especially in high-cold areas,due to the periodic changes in surface temperature,the free water in the soil drops below the freezing point in winter,and the water turns into ice and the Volume of soil body becomes larger,the phenomenon of frost swelling occurs in the upper part of the roadbed structure.Based on the National Natural Science Foundation of China(NSFC)project "Research on the mechanism of frost and swelling action and deformation characteristics of roadbed soil of new pile slab structure system for high speed railway in monsoon freezing area",this paper proposes a new roadbed structure applicable to alpine regions-a new pile slab structure roadbed with insulation slab.Through soil physical and mechanical tests,model tests,and numerical simulation calculations,the characteristics of temperature,moisture,and deformation of pile-slab structure roadbeds during the freezing period in winter in alpine regions,as well as the development laws and influencing factors,were analyzed,and the following main conclusions were obtained.1.Silty sand is a poorly graded soil with a permeability coefficient between sand and clay.The maximum dry density is about 1.8.The shear strength will first increase and then decrease with the increase of water content.When freezing,the confining pressure and temperature have a great influence on its strength.With the decrease of temperature and the increase of confining pressure,the strength increases linearly.2.In order to solve the three-field coupling equation of water-heat-force,the Fourier heat transfer equation and the Richard water migration model are solved simultaneously,and the mass ice content after freezing is solved,and then it is brought into the stress field equation to obtain the calculation model,Compared with the actual value measured in the experiment,the feasibility of the calculation model is verified.3.The temperature of shallow soil changes exponentially with the freezing time,and the deep soil changes linearly with the freezing time;the freezing depth changes exponentially with time,and the maximum freezing depth decreases with the negative temperature at the same time,The freezing depth changes exponentially.4.The pile-slab structure can effectively suppress the frost heave of the soil.In the pileslab structure,the bearing plate will warp during the frost heave process.The warping rate increases linearly with the decrease of temperature.Therefore,the pile-slab structure will be frozen during the freezing process.Stress concentration occurs at the junction of the pile and the slab.In the actual construction of the project,reinforcement measures should be taken here.5.The maximum freezing depth of the lower part of the load-bearing board presents an exponential function with the thickness of the insulation board.The range of ice content in the lower part of the pile-slab structure decreases with the increase of the thickness of the insulation board.As the plate thickness increases,the maximum displacement of the upper part of the load-bearing plate decreases,and the rate of decrease first increases and then decreases,showing an exponential function law.6.After reasonable calculation,the thickness of the insulation board is greater than 20 cm,in the alpine region in the winter freezing period of 5 months of extreme weather,the new pile plate structure roadbed both in strength and stiffness can meet the applicable conditions.