Why the risk of “collapse” of the bridge that supports the water supply was overlooked December 9, 13:08

One photo taken by an expert heading to the site after the collapse of a large-scale water pipe bridge "Aqueduct" in Wakayama City in October.

I caught the appearance that the members supporting the remaining part were broken in some places.

There was a possibility of further collapse, but no one was aware of the incident until the accident.

Why was the risk overlooked?

The facts revealed by experts in Ehime Prefecture and the subsequent interviews have revealed the "blind spot" hidden in our hearts.

(Matsuyama Broadcasting Station reporter Eihei Shimizu)

What triggered the collapse that happened without warning?

"Water pipe bridges" are "bridges" for sending water used for water supply and industrial water, and many are installed all over the country.

On October 3, a large "water pipe bridge" of about 500 meters suddenly collapsed in Wakayama City.

Fortunately, there was no human damage, but the impact was serious, with about 60,000 households and nearly 40% of the city's water outage.

What was the trigger?

Associate Professor Shinichiro Mori, who is studying disaster prevention measures for infrastructure at Ehime University, has begun an on-site investigation to find out the detailed cause.

In the video of the surveillance camera released by the Ministry of Land, Infrastructure, Transport and Tourism, it has collapsed into two without any sign.

What I paid attention to was the shape of the rhombus when it collapsed.

Associate Professor Mori

"The top and bottom of the arch are separated. This means that the" hanging material "in the middle is cut off."

The collapsed aqueduct has a structure in which the "pipe" through which water passes is supported by "arches" and "hanging materials."

According to Associate Professor Mori's analysis, the "hanging material" in the middle was cut off, causing the pipe to collapse without being able to support it, resulting in a "rhombus" shape.

The "hanging material" is fixed with fasteners such as bolts, and rainwater and bird droppings tend to collect in those parts.

Therefore, it is quite possible that it causes rust and corrodes the hanging material.

“It's okay to fall anytime”

Associate Professor Mori, who headed to Wakayama City two days after the collapse, sees an unbelievable sight to investigate the situation in more detail.

Of the remaining parts of the hanging material that did not collapse, four were completely torn.

Associate Professor Mori

"It's completely

open

. It was shocking. You can tell at a glance, no matter who says anything. It was in a state where it could run out anytime."

If left as it is, it may lead to further accidents.

Associate Professor Mori immediately contacted the administrator, Wakayama City, and the city also confirmed the breakage in a drone investigation on the 6th of the following day.

It was a shocking sight to support the possibility that "hanging material" was involved in the collapse.

Risk continued to be overlooked

But Associate Professor Mori said something even more surprising.

"This fishing material is likely to have been out for quite some time."

The cross section of the cut fishing material was "layered" with rust on top of it.

Associate Professor Mori

"This is not the case in a month or two. I think it had been broken for another year or so."

When Associate Professor Mori used the function of the map app to investigate the situation of the aqueduct in the past, it was found that the twill material had run out 10 months before the collapse in December last year.

Wakayama City conducts regular inspections once a month, and it was inspected in September, the month before the collapse, but no abnormalities were found.

Obvious risks may have been overlooked over the long term.

Immediately after the accident, Mayor Masahiro Obana of Wakayama City admitted that he was inadequate, saying, "I couldn't confirm it by visual inspection. I have to say that the inspection was unsatisfactory."

In the "blind spot" of the heart?

"Why couldn't I find such an obvious break?"

I've been wondering since I was shown a photo in the lab.

As we proceeded with the interview, it became clear that the risk of the water pipe bridge may not be limited to Wakayama City.

Matsuyama City also manages and inspects 87 aqueducts in the city.

However, it is said that the main part of the inspection is the "piping" where water flows.

Director Ikeda

"There was a strong awareness that we had to check the main body of the water pipe because there is a risk of water leakage if the pipe is rusty or damaged. There was no"

By accompanying me, I learned the details of the inspection.

For those who manage water services, the most important thing is "whether there is a leak."

Therefore, we pay attention to "plumbing", but the other parts are relatively less important.

So to speak, it was a "blind spot".

This was also reflected in the "check sheet" used by Matsuyama City for inspections.

The staff will check for water leaks and rust while pointing and checking in pairs, and write them down on the "check sheet".

However, although there are items such as "tube" and "air valve" on the check sheet, "hanging material" and "arch" are not found.

It is said that it is summarized in the item "joint part".

The person in charge of the city felt a strong sense of crisis.

Tetsuya Ikeda, Director, Matsuyama City Waterworks Pipeline Management Center

"Once a break occurs, it causes a great deal of inconvenience to the citizens. We must urgently review the inspection frequency and check method."

We have already reviewed the "inspection table"

Not only Matsuyama City but also Ehime Prefecture is independently reviewing its inspection system.

The prefecture manages 15 water pipe bridges for industrial water, but like Matsuyama City, the check sheet did not have the word "fishing material".

However, immediately after the accident, we started to review the method, and "fishing material" was added to the item of the new check sheet under consideration.

Furthermore, the number of items for the "arch part", which used to be one, has increased to four, and it is clear that the intention is to focus on inspections for parts other than the "piping".

Mr. Noguchi

"There is still a part where the line of sight was centered around the water pipe. I think that we can improve the inspection by keeping it as a record and being aware of it."

To verify how widespread these improvements are, we surveyed all local governments in Ehime prefecture.

As a result, it was found that there are at least 300 water pipe bridges in the prefecture, including small ones.

It became clear that about 60% of the cities and towns that manage the aqueduct felt problems with the inspection, and about 70% were planning to review the inspection method of the aqueduct in the wake of the accident.

Questionnaire results

* Of the 16 municipalities that manage aqueducts in Ehime Prefecture,

▼ I feel a problem with inspection ... 62% (10 municipalities)

▼ Review the inspection method ... 69% (11 municipalities)

"Limited visual inspection"

"Diagnosis varies from staff to staff"

Some local governments said that such voices were heard one after another, and the problem was first noticed in the wake of the accident.

To eliminate the aging infrastructure "blind spot"

After starting this interview, I became aware of the existence of a "water pipe bridge" for the first time.

If you walk along the river in Matsuyama city, you will notice that there are several water pipe bridges.

Birds such as "great cormorants" and "shirasagi" are lined up on the bridge, and I remember the words of Associate Professor Mori, "I think the bird droppings caused the corrosion."

It should be in my eyes, but I can't find it unless I'm aware of it.

Everyone has a "blind spot in their hearts", and unexpected accidents always occur in that gap.

As with local governments in Ehime Prefecture, water managers nationwide must thoroughly review the maintenance system as a lesson from the accident and make efforts to prevent the same thing from happening again.

Infrastructure facilities, including water pipe bridges, were built nationwide during the period of high economic growth, and many of them have been built for 40 or 50 years, and more and more have exceeded their useful lives.

How to manage the aging infrastructure and protect people's lives and safety.

I would like to continue to ask questions so that the "blind spot of the heart" does not cause similar accidents.

Matsuyama Broadcasting Station Reporter

Eihei Shimizu Joined in

2008 Kumamoto

After that, the Social Affairs Department covered disaster reports, and the Sports News Department focused on sumo wrestling and martial arts.

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