Research On Thermal Insulation And Cooling Technology Of Deep-Buried Super-Long Highway Tunnel With High Ground Temperature

China is rich in geothermal resources,especially in Tibet,Yunnan,Sichuan and other places.When carrying out tunnel construction in these areas,it is inevitable to encounter the problem of high temperature heat damage.For high ground temperature tunnels,high temperature will have a great impact on tunnel environment,supporting structure,construction machinery and personnel,and will bring many problems to the design and construction.Based on the Nige tunnel of Jianshui(Gejiu)to Yuanyang Expressway in Honghe Prefecture,Yunnan Province,this paper studies the heat insulation and cooling technology of deep-buried super-long highway tunnel with high ground temperature by means of literature research,field monitoring,numerical simulation and theoretical calculation.The main research contents and conclusions are as follows:(1)A numerical model is established by finite element software for calculation,and the influence of the hydration heat of the lining concrete during the construction period of the high ground temperature tunnel on the thermal insulation layer and the temperature field of the lining is analyzed.During the first and mid-term maintenance of the secondary lining,the insulation effect of the insulation layer is reduced by high temperature and double-sided heating.The existence of the insulation layer hinders the transfer of heat from the surrounding rock to the secondary lining and the cave,but it also makes it difficult for the heat of hydration generated by the secondary lining to transfer heat to the surrounding rock through the insulation layer,resulting in heat accumulation behind the secondary lining,which increases the peak temperature of the second lining by 14.9%.Comprehensive analysis of the influence of convective heat transfer coefficient and insulation thickness on temperature,combined with the on-site ventilation equipment configuration,the thickness of the insulation layer should be 9cm and the air volume of 2274.3424m~3/min should be provided,and the laying method is recommended to be sandwich type,It can achieve a better cooling effect while ensuring economy.(2)Cooling measures such as ventilation,ice,spraying,water sprinkling,and artificial cooling are used in the Nige tunnel.The fluid calculation software Fluent is used to calculate and analyze the cooling effect of four groups of working conditions:single ventilation duct,double ventilation duct,double ventilation duct with spray,double ventilation duct with ice.The results show that the temperature within 30 meters behind the tunnel face can be reduced within a few minutes under all working conditions,and basically maintained at a stable value.And with the increase of the distance from the tunnel face,the decrease of temperature has hysteresis.Furthermore,as the temperature of the surrounding rock increases,there is no significant change in the time required for the temperature to stabilize within 30 meters behind the tunnel face.The increase is only the temperature value and temperature drop value at the time of stability.Finally,the applicable range of each measure under different rock temperatures was determined,and a comprehensive cooling system was constructed.(3)The comfort level of tunnel personnel is mainly affected by geological conditions,construction conditions,geographical environment and thermal insulation and cooling measures,and a total of 19 influencing indexes such as rock temperature,burial depth,excavation method,insulation layer,ice cube and ventilation are proposed.Then the AHP-Extenics evaluation model was established to evaluate the comfort level of personnel.The results show that the personnel comfort level of Nige tunnel isⅠ,and the construction personnel can carry out the construction comfortably on the whole.Finally,a personnel protection design process is constructed based on the AHP-Extenics evaluation model to ensure that the comfort of the personnel in the tunnel meets the requirements.