| With the development of China’s economy,the scope of transportation infrastructure is becoming more and more extensive,followed by the construction of more and more tunnels in high and cold regions with high altitude,and the construction and operation of tunnels in cold regions are prone to encounter the problem of freezing damage,which will affect the stability of tunnel structure and threaten driving safety.Therefore,it is of great significance to study the temperature field and frost heaving force of tunnels in cold regions.Based on Yanchong high-speed chessboard girder tunnel project,by means of field monitoring,the literature research,numerical simulation and theoretical derivation,this paper studies the temperature field,the influencing factors of frost heave force and anti-freezing measures in tunnel.The influences of surrounding rock conditions and heat transfer coefficient on temperature field and frost heave force under the condition of random crack of surrounding rock are explored.At the same time,a calculation method of insulation layer thickness considering surrounding rock conditions and temperature conditions is preliminarily discussed.The main results and conclusions of this paper are as follows:(1)Through on-site monitoring of the ambient temperature in the chessboard beam tunnel,it can be found that in the import and export section of the tunnel,with the increase of the distance into the hole,the average temperature and minimum temperature of the hole environment are increased,the maximum temperature shows a trend of gradually decreasing and gradually stabilizing,the average temperature of the import and export section varies consistently,the temperature at the export is lower than at the import section.(2)The influence of the latent heat of seepage and phase change on the temperature field was studied by establishing a model considering random cracks.Analysis found that,when considering the seepage and the effect of phase transition,compared with not considering both,the surrounding rock temperature has different degrees of improvement.When considered the role of both,the effect will be more apparent.As a result of the existence of random crack and seepage,the distribution of circumferential temperature field in surrounding rock is not symmetrical.The circumferential temperature of surrounding rock shows a low and small variation in the range from the vault to the side wall,while the temperature from the side wall to the invert gradually increases.(3)To study the effect of different factors on the temperature field,it is found that the frozen depth of surrounding rock decreases with the increasing of porosity,permeability,heat capacity and initial temperature of the surrounding rock,and increases with the increasing of thermal conductivity and heat transfer coefficient.According to the calculation of sensitivity,various factors affecting the change of frozen depth sensitivity order from large to small is: Initial ground temperature,specific heat capacity,porosity,thermal conductivity,heat transfer coefficient and permeability.(4)The influence of porosity,elastic modulus of surrounding rock,thermal conductivity,specific heat capacity and heat transfer coefficient on the stress of lining structure and surrounding rock is studied.It is found that the change of porosity causes the biggest change in the stress of lining and surrounding rock,followed by the elastic modulus of surrounding rock and the smallest thermodynamic parameters.The stress distribution of the lining structure shows that the tensile stress at the side wall is the largest,the compressive stress at the arch foot is the largest,and the stress at the invert is the smallest.(5)In the aspect of insulation and antifreeze of tunnels in cold regions,the corresponding water treatment measures are put forward from the aspects of surrounding rock grouting waterproof,tunnel lining waterproof and tunnel lining drainage.In terms of the thermal insulation layer,the frozen depth is selected as the evaluation index,the porosity of surrounding rock,the thermal conductivity of the surrounding rock skeleton,specific heat,initial ground temperature environment temperature in the hole are the influencing factors,the orthogonal experiment was carried out.Multiple linear regression analysis is made on the orthogonal test results,and a prediction model of freezing depth and influencing factors is established.Based on this,the existing formulas for calculating the thickness of insulation layer are revised,and a method for calculating the thickness of insulation layer considering the conditions of surrounding rock and temperature is preliminarily discussed. |
