Research On Technique Of Antifreeze And Preservation For Tunnel Portal In Seasonal Frozen Regions

On earth,frozen soil(including instantaneous frozen soil,seasonal frozen soil and ever-frozen soil)covers about 50% of the total area of the land;China’s seasonal frozen soil is distributed in most of the land,including the west vast area of Helan Mountain to Ailao Mountain line,and the north line of Qinling-Huaihe region.With the rapid development of China’s economic construction,the demand of Construction is increasing.The quantity of existing tunnels and new tunnels in the seasonal frozen earth area is huge and more frost damage occurred in these area,and the frost disaster of tunnel are: ice and water seepage in tunnel lining,the emitting water and ice frost of tunnel bottom,lining crack.The results of the investigation and analysis of the disease in the 55% of the cold region in the cold region of the area show that the strength of the frost is the source of the destruction of the tunnel deformation in the cold region.On the other hand,the effect of permafrost increases the weathering effect of the surrounding rocks,and the increase in the extent of the fracture of the surrounding rock provides a more favorable condition for the increase of the freezing expansion.The results show that the temperature of the tunnel that along the tunnel is roughly parabolic in the seasonal frozen soil is low in the middle section and high in the import and export section during the warm season.In the cold season,the middle is high and the inlet and outlet sections are low.Therefore,the cold region tunnel freezing injury occurred in the import and export section of the location as the tunnel frostbite prevention and control of the key parts.The anti-freezing research in seasonal frozen earth tunnel is firstly started from the entrance section of the anti-freezing.The entrance section relatives to the non-cave section is not only influenced by the tunnel entrance air temperature,but also by the external atmosphere,which is the hardest hit by the temperature inside and outside.Without anti-freezing the entrance section,the non-cave section will become the hardest hit as well,then the entire tunnel anti-freezing will have no effort.In order to do the seasonal frozen earth tunnel insulation from cold damage,we must ensure the entrance from the cold damage firstly.So the purpose of this study is about anti-freezing technology research in the seasonal frozen earth tunnel section.On the basis of summarizing current research situation and related theoretical knowledge,this paper sets the seasonally frozen earth tunnel in Qinghai as an example and firstly considers the local meteorological elements,and uses the limited volume software(FLUENT)to the whole of the Tunnel in Qinghai by numerical simulation.The convective heat transfer law of surrounding rock and tunnel is studied,and the temperature distribution function of tunnel wall is fitted.The function and structure of air fitting functions are similar,both amplitude and phase change is not obvious,the timeliness is basically the same with the actual situation of the two is almost the same time affected by wind temperature field is consistent,mainly by the outside air temperature change direction and the original ground temperature field that influence each other.As a function of the load,the temperature field of a tunnel entrance in Qinghai was simulated by APDL software ANSYS.Further,the ansys numerical simulation of the frost heave force of the surrounding rock of the tunnel is carried out:First of all,within the outer atmosphere and hole temperature,under the dual role of formed a circle around the hole the temperature effect reinforcing band,the obvious feature of strengthening belt is isothermal curve interval is larger than elsewhere,and with the increase of hole deep,isotherm spacing is smaller;Second,the lower the temperature of the tunnel opening,the higher the radial temperature.Finally,the area of the freezing circle,as the distance of the hole increases,the freezing circle decreases.Then the information is got that the size and development regularity of the frost heave force.The equivalent frost heave stress at the arch is the largest,and the frost heave force of lining is different with the maximum is 10.9 MPa which is enough to destroy the tunnel lining.The main reason for the maximum equivalent freezing stress in the elevation of the section of the cave is the maximum depth of freezing,and the boundary conditions are relatively concentrated here.The freezing circle has a large equivalent freezing stress in the direction of the temperature wave.Finally aimed at the characteristics of seasonal frozen soil tunnel portal section of frost heaving stress field,puts forward the technology of grouting waterproof antifreeze question and concern,advocate loose boundary of surrounding rock of tunnel entrance section of advice.According to the entrance section of the temperature field and frost heave stress field,the traditional anti-freezing and heat preservation technology is analyzed as well as the comprehensive measures of anti-freezing and heat preservation technology in this paper.The comprehensive measures are mainly focus on the thermal insulation door and assisted by heating technology,drainage antifreeze technology,loose surrounding rock boundary,strengthening the technical measures of tunnel lining.What is more,using numerical simulation verifys the reliability of insulation measures combined with the cold insulation doors and heating technology.Among them,FLUENT is related to the temperature field coupling of the air flow and the solid.The ANSYS is related to the thermal stress coupling,and the seepage field is considered in the whole process.Seasonal frozen soil tunnel portal section of freeze protection is a key step of the whole tunnel freeze protection,leading step,only the mouth of the cave for freeze protection first,to do the whole tunnel freeze protection well.