On days when only 3-4 stones can be piled up per day… “Kumamoto Castle Restoration Work”: Why is the complete restoration delayed for 15 years & what is the current situation?

The “hard-to-attack castle” structure was a “blunder”…

Kumamoto Castle was severely damaged by the 2016 Kumamoto earthquake. The city of Kumamoto announced in November that it expects the castle to be fully restored in 2052 (30 years from now), 15 years behind schedule. Was the outlook too optimistic?

You may think so. But in the past, there was no damage such as this large-scale stone wall collapse, and we had no information to refer to.

So, we assumed 20 years, referring to castles damaged in East Japan, although the scale was different, but the damage was greater than we had expected.

So in 2022, five years later, we reviewed the plan and decided that full restoration would be in 2052, 35 years after the earthquake.

Yasuhiro Iwasa, deputy director of the Kumamoto Castle General Office, said.

There are various reasons why the restoration work has not progressed as expected, he says. One of them is that the damage to the stone walls varies widely. Some have collapsed, while others have been pushed out from inside the stone walls and have bulged out. Some stonewalls have turrets on them, others do not. The restoration method depends on the stonewalls.

The stone walls built by Kiyomasa Kato and those built by his son, Tadahiro, have undergone technical innovations such as steepening the angle of the slope. The way the stones are piled up also differs depending on the period.

Kumamoto Castle is designated as a national special historic site, so in order to protect its value as a cultural asset, we must reproduce the shape of the castle at the time it was piled using the techniques of the time. We do this carefully one by one,” said Iwasa.

The collapsed stone walls are numbered one by one and put together like a jigsaw puzzle. I thought that once all the stones were numbered, all that was left to do was to pile them up.

But that’s not the case at all,” said Iwasa.

But he was met with a laugh.

Even if the stacking locations are correct, the stones all have different shapes, and in order for them to support each other, we have to determine which of the irregularly shaped stones were the points of contact before stacking them. Sometimes we can pile more than 10 stones, but sometimes we can only pile 3 or 4 stones in a day,” said Iwasa.

Three or four a day!　This may take 35 years, but it is not unreasonable.

Issues are being revealed one after another, and even after five years, the restoration method for some stonewalls has not been decided.

Another issue that is worrying the local people is how to ensure safety.

If you pile up a collapsed stone wall as it is, it may collapse again. It is a bit of a contradiction in terms to maintain safety while not damaging the value of the cultural asset, so it is also a challenge.

Tatsuo Amida, director of the Kumamoto Castle Research Center, said, “It’s a tough job. Mr. Hiroki Tateishi, Technical Counselor of the Kumamoto Castle General Office’s Civil Engineering Group, also commented, “From a civil engineering point of view, the current technology is not robust enough.

From a civil engineering standpoint, we can make the castle more robust using current technology, but when cultural assets are added to the mix, we have to think of new ideas that go beyond what we know so far. I am learning every day.

For example, there is a method of covering stone walls with nets to stabilize them.

For example, there is a method of covering stone walls with netting to stabilize them. “From the viewpoint of preserving their value as cultural assets, we can’t reinforce them excessively. The basic principle is to use minimal reinforcement only where it is truly necessary,” says Iwasa.

In some cases, however, the structural calculations were not limited to desk calculations, but a one-eighth scale model was made of the most important areas and subjected to earthquake vibrations.