海底盾构隧道管片接头氯离子侵蚀运移规律研究

Research on Chloride Ion Erosion and Migration in Segment Joints of Undersea Shield Tunnels

随着海底隧道服役时间的延长,氯离子侵蚀对衬砌结构的危害会不断递增,需对此进行深入研究。文章从多孔介质中腐蚀离子运移机理出发,采用渗流与离子运移耦合分析的方法,建立了管片接头氯离子侵蚀运移数值模型,重点分析管片接头位置在海底氯盐环境长期侵蚀作用下的氯离子侵蚀运移规律,得到的主要结论有:孔隙水是氯离子在管片混凝土中侵蚀运移的载体,氯离子在管片中侵蚀运移作用主要包括对流、分子扩散、机械弥散等;随着隧道服役时间的延长,氯离子从管片接头外表面向隧道内部渗透的深度越大;隧道外部水压对管片渗透速度与深度影响显著,外部水压越大海水渗透深度越深;接头局部区域的氯离子侵蚀体现出不均匀分布现象,氯离子浓度较远离接缝处较高,到达临界浓度的时间也较短;近接缝面位置处由于边界条件不同及不连续的影响,存在氯离子运移曲线轨迹。

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 po- rous medium, we have set up a numerical model of chloride ion erosion and migration for segment joints by analyz- ing 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 diffu- sion and mechanical dispersion. With a long in-service time, the chloride penetration depth increases from the out- side surface of the segment joint to the interior, and external water pressure has a significant effect on the penetra- tion 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.