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Research on Chloride Ion Erosion and Migration in Segment Joints of Undersea Shield Tunnels
(Key Laboratory of Transportation Tunnel Engineering, Ministry of Education, School of Civil Engineering, Southwest Jiaotong University, Chengdu 610031)
Abstract Since lining structure damage caused by chloride ion erosion increases with time for in-service subsea tunnels, an in-depth study of this process is necessary. Based on the migration mechanism of corrosive ions in a porous medium, we have set up a numerical model of chloride ion erosion and migration for segment joints by analyzing the coupling seepage and ion migration, with a focus on the erosion and migration law of chloride ions at segment joints under the long-term chloride salt erosion environment of the sea bottom. We conclude that pore water is the carrier of erosion and migration of chloride ions in concrete segments, which includes convection, molecular diffusion and mechanical dispersion. With a long in-service time, the chloride penetration depth increases from the outside surface of the segment joint to the interior, and external water pressure has a significant effect on the penetration velocity and depth of the affected segment, which means the higher the external water pressure, the deeper the penetration depth. An uneven distribution of chloride ion erosion occurs in the local area of the joints, where there is a higher chloride ion concentration with a shorter time to reach a critical concentration (than in areas farther away from the joints). Finally, a specific chloride migration curve trajectory exists near the joint surface due to different boundary conditions and the influence of discontinuities.
Abstract：
Since lining structure damage caused by chloride ion erosion increases with time for in-service subsea tunnels, an in-depth study of this process is necessary. Based on the migration mechanism of corrosive ions in a porous medium, we have set up a numerical model of chloride ion erosion and migration for segment joints by analyzing the coupling seepage and ion migration, with a focus on the erosion and migration law of chloride ions at segment joints under the long-term chloride salt erosion environment of the sea bottom. We conclude that pore water is the carrier of erosion and migration of chloride ions in concrete segments, which includes convection, molecular diffusion and mechanical dispersion. With a long in-service time, the chloride penetration depth increases from the outside surface of the segment joint to the interior, and external water pressure has a significant effect on the penetration velocity and depth of the affected segment, which means the higher the external water pressure, the deeper the penetration depth. An uneven distribution of chloride ion erosion occurs in the local area of the joints, where there is a higher chloride ion concentration with a shorter time to reach a critical concentration (than in areas farther away from the joints). Finally, a specific chloride migration curve trajectory exists near the joint surface due to different boundary conditions and the influence of discontinuities.
LIU Si-Jin- Sun- Qi- Feng- Kun- He- Chuan
.Research on Chloride Ion Erosion and Migration in Segment Joints of Undersea Shield Tunnels[J] MODERN TUNNELLING TECHNOLOGY, 2016,V53(6): 100-107
2016, Vol. 53 