On the night of the 27th, a collapse occurred at the construction site of a tunnel on the Linear Chuo Shinkansen in Nakatsugawa City, Gifu Prefecture, killing and injuring two workers.

From the interviews by JR, we can see the details of the accident.

I've summarized in detail where and what happened.

1. Where is the accident

The accident occurred at the construction site of the "Seto Tunnel" in Seto, Nakatsugawa City, Gifu Prefecture.

According to JR Central, the "Seto Tunnel" is located between the stations planned to be constructed in Nagano and Gifu prefectures, and the total length is 4.4 kilometers in the plan.

Construction started in January 2019, but construction on the main line has not yet begun.

Currently, construction is underway to dig an "emergency exit tunnel" of about 600 meters leading to the main line, and the accident occurred about 70 meters from the entrance of this tunnel.

2. What kind of construction

According to JR Central, the construction was carried out by the same method called "NATM construction method" as general tunnel construction.

This method is mainly used for tunnel construction in mountainous areas. Explosives are installed in the places where you want to dig, explode, scrape out the earth and sand with heavy machinery, and then the walls are hardened with concrete or bolts.

In September, a photograph of the site taken by JR Central shows that a heavy machine called "drill jumbo" was used to make a hole in the wall for explosives inside a tunnel about 7 meters high and 9 meters wide. It is shown that the process is proceeding.

You can see that the inner wall of the tunnel that has been excavated is concreted.

3. What happened

According to JR Central, which held a press conference on the afternoon of the 28th, at around 7:20 last night, while digging an emergency exit tunnel, the ground collapsed inside the tunnel after exploding explosives.

Takayuki Koita (44) from Mihama Town, Fukui Prefecture, died in the accident, and a 52-year-old man in Nagakute City, Aichi Prefecture, suffered serious injuries such as a broken leg.

After the explosive explosion, five workers were inspecting for unexploded ordnance, and a small collapse occurred that caused the upper surface of the tunnel to peel off, burying Koita's feet. It means that.

When a nearby worker tried to rescue him, the rock near the ceiling collapsed over a length of 2 meters, a width of 1 meter, and a thickness of 50 cm, and two people were involved.

This is the first time that a fatal accident has occurred during the construction of the Linear Chuo Shinkansen, and the police are investigating the site in detail regarding safety management, etc., considering that there is a suspicion of accidental fatal injury in business.

4. Tunnel engineering experts

Professor Emeritus Tanimoto of Osaka University, who specializes in tunnel engineering, said, "In the emergency exit where there was an accident, various deposits overlap on the hard ground," after looking at the cross-sectional view of the ground surface published by JR Central. It is possible that the construction was done in a fragile, weak layer before reaching the hard ground. "

Furthermore, "After blasting work, it is easy for the surface to fall from cracks on the tunnel wall, which is the most dangerous condition in tunnel construction. It seems that an accident occurred during the work to eliminate the danger such as intentionally dropping the tunnel. "

On top of that, "Since this work is a common sense work for tunnel construction, it is considered that it is an accident that rarely occurs if the site is well supervised and skilled workers are performing the construction. Such an accident is linear. We must take what happened during the construction, analyze the cause, and share it with another construction site. "

5. Landslides in the past

Construction of the Linear Chuo Shinkansen is progressing in various places, but landslides have occurred around the tunnel construction site.

In Nakatsugawa City, Gifu Prefecture, the work tunnel for the construction of the "Central Alps Tunnel" and the earth and sand of the thickets above the tunnel collapsed.

It seems that the cause was that a construction method that was not suitable for the ground at the site was used, so JR Tokai reviewed the construction method to strengthen the support of the tunnel, and if necessary, ask a geologist to make a decision to prevent recurrence. Is shown.

6. Impact on construction period

The Linear Chuo Shinkansen aims to open between Shinagawa and Nagoya in 2027.

However, Shizuoka Prefecture, which is concerned about the impact on water resources such as the Oi River, has not approved the start of tunnel construction in the prefecture, and discussions have been difficult, making it difficult to open as planned.

Under these circumstances, this accident happened.

Regarding the impact of the accident on the plans for the Linear Chuo Shinkansen, JR Central's executive officer Kenichi Niimi said at a press conference on the evening of the 28th, "I don't think there will be a significant impact on the project."

However, due to safety measures, the landslide caused by the tunnel construction in Nakatsugawa City, Gifu Prefecture, has been suspended for about 7 months in the 4.7 km section connecting Gifu Prefecture and Nagano Prefecture.

This is the first fatal accident in the construction of the Linear Chuo Shinkansen, and since it is necessary to further investigate the cause and strengthen safety measures, there are concerns about the impact on the construction period.