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  Chloride attack countermeasure construction of subway caisson tunnel under the river

  Tokyo Metro Co., Ltd. operates 9 lines, 195.1km of total length, in Tokyo. 7.24 million passenger use our lines every day in last year. It is the traffic artery in the capital city of Japan. About 85% of the total length, 166.7km, is composed of tunnel. In these tunnel, there is a place which is particularly caused deterioration due to chloride attack under tidal rivers. In order to examine medium-and-long term prevention maintenance measures for tunnels, We arranged occurrence condition of chloride attack. As a result of a detailed investigation by , the caisson tunnel near the tidal river of the Tokyo metro Co.,Ltd. chloride attack due to water leakage that contains the seawater and the equivalent of salt in the joints between the box-body has occurred. Was also carried out the measures of Engineering in the past with respect to this chloride attack point, it was confirmed that the subsequent re-degradation is happening. In recent years, this chloride attack for the occurrence conditions, research and analysis of the occurrence range, performs a comprehensive examination such as examination of the development and drastic repair method of a simple survey methods required range of repair, to ensure against chloride attack was to repair can be like. In this paper, we report on the chloride attack countermeasure work a combination of sacrificial anode material engineering and a cross-sectional repair factory using a sacrificial anode material that details and the current implementation of the results of these studies. This paper report the followings. 1) Previous study and countermeasure for chloride attack, 2) Countermeasure policy for chloride attack, 3) Overview of Countermeasure construction. Finally, Countermeasure construction has several task. In particular, for long-term tunnel management, we have to decide the replacement cycle of sacrificial anode material. In order to do that, it is important to grasp the change on standings of sacrificial anode material based on monitoring survey.

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