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Report on Causes of Water Leaks

Final update date March 5, 2019

 We report on the cause investigation of water leakage accidents.

Tarumachi 2-chome valve damage cause investigation report

 This report summarizes the contents of the examination by the "Tarumachi 2-chome Balb Damage Cause Investigation Committee" conducted in November 2017.



 Following the water leakage caused by the damage of the 800 mm diameter valve that occurred at Tarumachi 2-chome, Minato-ku on January 22, 2016, the cause of the damage and the direction of future measures to prevent recurrence were shown. . The setting of the survey items uses the FTA survey method, and based on the survey results, the cause of the damage is assumed. Finally, the direction of response is shown from two perspectives in response to the expected cause of damage.

Progress in Measures to Prevent Recurrence

 From 4,281 valves with a diameter of 400 mm or more, we extracted 100 valves installed under the same conditions as damaged valves.
 In order to prioritize and respond to the 100 units, we classified them into priority A to C.

Number of valves by priority

Number of valves by priority
Priority Classification Number of valves
A. The impact of land subsidence is significant, and the highest priority is needed. 7 units
BB Balves that require continuous monitoring are expected to progress in land subsidence. 73 units
CC valves that are not expected to be affected by the ground or piping that caused the damage 20 units
Total 100 units

 Regarding the seven units classified as "Priority A" (one of them has been removed due to the replacement of aging pipes in FY2017), we investigated cracks in protective concrete that can be quickly confirmed among the causes of damage, but immediately No cracks were found that could lead to damage.
 In the future, six valves of "Priority A" and four units that are assumed to have a large subsidence of the surrounding ground will be selected from the valve of "Priority B", and the subsidence of the ground, which is the cause of damage, In order to actually check the piping from the valve, we will conduct a trial drilling and visual inspection of the valve room.
 If any abnormalities are found in the exploration or visual inspection, we will promptly update them.

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Water Distribution Division, Water Works Bureau Water Distribution

Telephone: 045-671-3064

Telephone: 045-671-3064

Fax: 045-212-1167

Email address: [email protected]

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