Research Of Environmental Division Of Metro Concrete Durability Based On Monte Carlo Method

At present,there are more than 5800 kilometers of the total subway operating mileage in China and the subway system has been built and operated in over 30 cities.Meanwhile,a large number of concrete structures are used in subway facilities.With the subway service life increasing,the durability of concrete structures has become a key issue.The cities in which subway system have been built and opened to traffic are widely distributed throughout the country,and the concrete service environment has obvious differences,and different service environments have different impacts on the durability of concrete.In order to improve the durability of subway concrete and maintain the operating capacity of urban subways,it is necessary to evaluate the durability of subway concrete reasonably,clarify the characteristics of subway concrete service environment in different regions,and scientifically divide it into a primary task.This article is based on the national key research plan,which is “Technology for Disaster Prevention and Capacity Maintenance of Rail Transit Civil Construction Facilities in Complex Environments”(2017YFB1201204).Centering on the durability of subway concrete,environmental analysis and zoning studies were conducted.The main research contents and results are as follows:(1)Through the analysis of the service environment characteristics of subway concrete,and drawing on the existing research results of the durability of the superstructure concrete,it is determined that the main factors of the subway concrete durability are carbonization,chloride ion erosion,freeze-thaw damage,and stray current erosion.This study is centered on carbonization and chloride ion erosion,which are also the main factors affecting the subway concrete durability in southern regions and coastal cities.(2)The mechanism of carbonization and chloride ion erosion and the main environmental impact factors are analyzed.The underground water environment of subways in Nanjing and Qingdao is investigated.Regarding environment as indicators of environmental zoning,the material parameters of the subway concrete life prediction model were unified.And the prediction models of concrete carbonation life and chloride ion erosion life are established respectively.(3)The environmental parameters(e.g.,the temperature and humidity of the environment,the concentration of carbon dioxide)are directly related to the carbonation degree of the subway concrete.In order to explore the change and distribution of the environmental parameters of the subway concrete and establish the correlation to the aboveground environmental parameters in the same area,the climate environment of the Nanjing subway station had been monitoring for four months.And then the change law with time between aboveground and underground temperatures,relative humidity,and carbon dioxide concentration are obtained.And the relationship between the aboveground temperature and station temperature is established.The regression analysis results show that the fitting results are good,which lays a foundation for the prediction of the life of subway concrete carbonization and chloride ion erosion.(4)On the basis of determining the material parameters of the subway concrete,respectively for carbonization and chloride ion erosion,the subway concrete life prediction model is established based on the Monte Carlo method.And based on the service life,the results of nationwide subway concrete carbonization and chloride ions erosion environmental regionalization are abtained.The recommended values for the thickness of the carbonized erosion protection layer,as well as measures to resist carbonization and chloride ion erosion are given.(5)Comprehensively considering the effects of carbonization erosion and chloride ion erosion,a comprehensive evaluation model of subway concrete life is established based on the variable fuzzy set theory.The practical engineering data of two cities,Nanjing and Qingdao,are used for example analysis.The analysis results show that the durability evaluation result of Nanjing Metro Line 1 is grade II(Great),and that of Qingdao Metro Line 2 durability is grade IV(Poor).The two results above are in line with actual engineering test results and fully verify the reliability of the model.