Study On The Law Of Freezing Damage Of Linings In The Tunnel Entrance Of Cold Area And Countermeasures

In recent years,with the rapid development of China's economy,the scale of investment in infrastructure construction has continued to expand,and China has built a large number of road tunnels and railway tunnels in cold regions.The construction of tunnel technology in cold regions is much more complicated than that in the general area.One of the key problems is that cold tunnels are generally affected by seasonal freezing and thawing and frost heaving.This periodic freezing and thawing and frost heaving will cause damage to the tunnel structure.The tunnel portal section generally has a shallow depth and is easily affected by the seepage of surface precipitation.The lining and surrounding rock near the entrance are affected by the change of external atmospheric temperature all the year round.It is easier to cause structural damage under the influence of temperature field,and the probability of freezing damage near the hole.It is much higher than the inner section of the cave.Therefore,the research focus of the cold tunnel is the cold insulation design near the tunnel entrance.Based on a tunnel in the cold area of the north of Hebei Province,the temperature field of the tunnel in winter is measured and analyzed.The influence of different factors on the temperature field of the cold tunnel is studied by numerical simulation method.The reasonable settings were studied and the stress variation law of the lining structure near the tunnel entrance in the cold area was studied.The main conclusions are as follows:(1)By analyzing and analyzing the actual measured data of a tunnel in the north of the cold area,the distribution law of the air temperature field of the tunnel in winter is obtained.The fluid analysis software FLUENT was used to establish a three-dimensional model of tunnel fluid-solid coupling transient thermal analysis under the dominant wind.The effects of three factors,namely inlet wind speed,ambient temperature and surrounding rock temperature,on the temperature field of the cold tunnel were simulated.(2)In order to study the thermal insulation effect and reasonable selection of the insulation layer,a two-dimensional model of tunnel section was established by using the finite element software ANSYS.The temperature field of the surrounding rock of the tunnel in the cold zone without insulation layer and insulation layer was calculated and analyzed.Distribution,research and analysis of the insulation effect of the insulation layer under different temperatures and different materials.Combined with the measured temperature data,the reasonable thickness and length of the insulation layer are analyzed and studied,which has certain reference significance for the design of the tunnel insulation layer in cold regions.(3)Based on the engineering background of a tunnel in the north of the cold area,a calculation model for the coupling of temperature field and stress field is established.The variation law of stress field and displacement field of the lining structure under the influence of temperature field is simulated and analyzed.Under the influence of the temperature field,the maximum tensile stress of the lining at the buried depth of 40 m is increased by 57.3% compared with the initial stress field,and the maximum tensile stress of the lining at the buried depth of 14 m is increased by 226.8% compared with the initial stress field.The tunnel section is subject to large frost heave force.Therefore,the influence of frost heave force on the lining structure should be considered in the shallow buried section of the tunnel.