Study On Frost Heaving And Control Measures Of Tunnels In Cold Regions By Thermo-hydro-mechanical Coupling Analysis

With the development of western plateau permafrost,northeast high latitude and other remote areas,the railway and highway transportation network rapidly extended to these areas,more and more tunnels in cold regions have been built one after another,and the frost heaving disasters are also increasing.Especially the Dongkou section is affected by severe cold weather such as rain,snow and storm all the year round.At present,there are few systematic studies on frost heaving damage,and the setting of cold protection measures mainly depends on engineering experience,lacking the evaluation basis of frost protection effect.Based on this,this paper uses the methods of literature research,numerical simulation and field monitoring to study the mechanism of surrounding rock frost heaving and the influence of related factors on frost heaving,and puts forward effective measures to prevent frost damage.The main achievements are as follows.(1)This paper introduces the mechanism of frost heaving of surrounding rock,the governing equation of hydro thermal coupling of tunnels in cold regions and the value method of hydro thermal coupling calculation parameters,which provides the theoretical and parameter basis for the later three field coupling numerical analysis of tunnels in cold regions.(2)Based on the existing Yuximolegai tunnel project,the "water heat force" three field coupling numerical model of tunnel frost heaving is established by using ABAQUS finite element software.The simulation process and the deformation and mechanical response of the tunnel caused by freezing and thawing of surrounding rock are analyzed in detail.It is found that during the freezing process of surrounding rock,the vertical displacement of vault,arch bottom and surface is upward,and the horizontal displacement of arch shoulder and side wall is inward,The deformation of arch foot is relatively small.The maximum principal stress on the outside of the arch foot and the inside of the invert is positive,and the lining is in tension,which are the most unfavorable positions of the lining,and the lining stress increases with the increase of the freeze-thaw cycle.In addition,the simulation results are compared with the field monitoring results of the built tunnel,so as to verify the accuracy of the model.(3)Based on the water force heat three field coupling model,the frost heaving process of Jianping tunnel is simulated and analyzed.The influence of temperature loading time,temperature extreme value,elastic modulus of surrounding rock and void ratio of surrounding rock on the frost heaving deformation and mechanical response of tunnel is studied.It is found that the influence of temperature and void ratio of surrounding rock on frost heaving is obvious.The thickness of frozen wall,lining deformation and lining stress increase with the increase of freeze-thaw period and void ratio,and increase with the decrease of minimum temperature.(4)The control measures to prevent freezing injury are studied from two aspects of drainage and heat preservation.By studying the anti freezing effect of deep buried central ditch,it is found that considering the extreme temperature load,0.3m under the inverted arch of the middle ditch can meet the anti freezing requirements.In addition,by studying the antifreeze control effect of the insulation layer,the upper and lower limits of the insulation layer length are obtained,and it is found that the 5cm insulation effect basically meets the antifreeze design principle.