Study On The Durability Evaluation Of Lining Structure In Sea Area During Subway Operation Period

With the continuous advancement of urbanization in China,the city's demand for subways is increasing.The eastern coastal cities of China have to build subsea tunnels because of their special geographical environment.The seawater contains a large amount of chlorine salts.During the service of the submarine tunnel structure,the structure will inevitably be eroded by chloride ions in the seawater,which will lead to a decrease in the durability of the tunnel lining structure.In addition,the eastern coastal areas of China are located in the circum-Pacific seismic belt.The earthquake will cause serious damage to the tunnel structure.What's more,in recent years,global earthquakes have occurred frequently.Therefore,higher requirements have been placed on the seismic performance of tunnel structures.The subsea tunnel is in a very complex geological environment and will be affected by sudden changes in seawater erosion,high water and soil loads,and earthquakes.In this paper,based on the shield tunneling project of Xiamen metro area,the bearing performance of the tunnel lining structure after degradation of chloride ion and its response under seismic load are analyzed.The research's results are as follows:(1)The factors affecting the durability of the submarine tunnel structure are introduced.The influence of chloride ions on the properties of the concrete and the mechanism of chloride ion penetration in the concrete are summarized.(2)Through the experiment of accelerating the erosion of concrete with chloride ions,the change of physical and mechanical properties of concrete after degradation of chloride ions was studied.It was found through experiments that the elastic modulus and compressive strength of concrete eroded by chloride ions were higher than those of un-eroded concrete.Obvious drop,after testing the shear wave velocity before and after the chloride ion erosion of the concrete test block,it was found that the shear wave speed of the concrete soaked with the chloride salt solution increased to some extent.(3)According to the actual situation of the project,the penetration depth of chloride ion in concrete with time is obtained through simulation calculation.It is found that as the etching time increases,the penetration depth of chloride ions in the concrete increases continuously,and in 10 to 100 years During the year,the depth of erosion of chloride ions has a linear relationship with time.(4)Using the parameters of concrete determined experimentally and the penetration depth of chloride ions simulated and calculated,the load-bearing performance of the shield tunnel after the chloride ion erosion is degraded is further simulated and analyzed.It is found that as the depth of chloride ion erosion deepens,the displacement deformation of the tunnel lining structure increases continuously,among which the maximum settlement displacement of the dome is;with the increase of chloride ion erosion,the maximum stress inside the tunnel lining structure increases continuously,while the safety factor decreases constantly.(5)Artificial seismic waves are generated based on the actual working conditions of the project and the local seismic fortification intensity,and the artificial seismic waves are introduced into the calculation model.The tunnel structure's service which is 50 years,100 years of erosion and without chloride ions are subjected to earthquake loads.The following response laws were analyzed and found:with the deepening of the chloride ion erosion of the tunnel structure,the internal stress of the tunnel structure showed an increasing trend,and the maximum internal stress of the tunnel structure from the uneroded state to the chloride ion erosion for 100 years increased about 13.2%.