Road collapse Tunnel construction deep underground To investigate the cause of unknown causality October 19, 19:58
On the 18th, a road was found to be depressed over a width of 5 meters in a residential area in Chofu City, Tokyo.
The East Nippon Expressway is constructing a tunnel deep underground in the vicinity, and on the evening of the 19th, the person in charge and experts of the East Nippon Expressway held a press conference and said that the causal relationship with the construction was unknown. It was revealed that it will not resume until it can be investigated.
The company will listen to experts to investigate its relationship with the depression.
On the afternoon of the 18th, the road in front of the house suddenly collapsed in a residential area at 2-chome, Tsutsujigaoka, Chofu-shi, Tokyo, and a hole with a width of 5 meters, a length of 2 meters, and a depth of 5 meters was opened.
In the vicinity of the site, the East Nippon Expressway is constructing the "Tokyo Outer Ring Road" 40 meters or more underground from the ground surface called the deep underground, and according to the company, a large machine excavating a tunnel in the middle of last month It means that it has passed.
Policy not to resume until it can be investigated without understanding the causal relationship
East Nippon Expressway staff and experts held a press conference on the evening of the 19th, and Waseda University chairman Atsushi Koizumi, an expert on the tunnel construction method study group, said, "Is there a causal relationship? I have to find out if it was there. It's too early to conclude. However, I can't say that there is no causal relationship, and I don't think it will drop suddenly. "
In addition, Kenji Kato, general manager of the East Nippon Expressway Construction Division, said, "No cracks or water leaks have been confirmed in the tunnel body deep underground, and no damage to the tunnel body has been confirmed." explained.
In the future, it is necessary to check the ground condition of the place where the depression occurred, so it is decided to proceed with boring investigation etc. to investigate the cause, and it was revealed that the construction will not be restarted until the cause can be investigated. ..
Response to East Nippon Expressway Residents
In addition, the East Nippon Expressway collapsed directly above the underground tunnel where excavation work is underway, so we called on the residents of 30 surrounding households to evacuate, noting that the causal relationship was unknown. ..
It means that no residents are currently evacuating because the emergency restoration of the road has been completed.
Regarding this, Kenji Kato, general manager of the Construction Division, said, "We are sorry for the inconvenience to the residents. We would like to take measures to investigate the cause so that we can return to our original life as soon as possible."
In addition, after clarifying that there were several reports from residents around the collapse site that there were cracks in the house from a month ago, "How many specific offers were made is being summarized and answered. I couldn't do it. I visited the house where I was offered to check the site, but it wasn't directly linked to the fact that it had a causal relationship with the construction, and I was only investigating because it was still under construction. I was talking.
In the future, we will continue to focus on monitoring the condition of the depressed area and the surrounding roads, and if there is a change in the road, we will respond promptly.
Construction proceeds deep underground between Kanetsu Expressway and Tomei Expressway
"Tokyo Outer Ring Road" = "Outer Ring Road" is one of the ring roads in the Greater Tokyo Area, and is a high-standard trunk line with 6 lanes and a total length of 85 km that connects Tokyo, Saitama, and Chiba in a ring for the purpose of alleviating traffic congestion in the city center. It's a road.
Of these, the section between the Kan-Etsu Expressway and the Tomei Expressway, which is about 16 kilometers north and south of Tokyo, is under construction at a depth of 40 meters or more from the ground surface called "deep underground."
Construction began in February
2017 from the Tomei Junction on the Tomei Expressway in Setagaya Ward, Tokyo
on the south side,
and is proceeding underground in Komae City and Chofu City.
The construction method is to dig a hole with the largest large machine in Japan with a diameter of about 16 meters, which excavates the ground called a shield machine, scrape out the soil, and attach the tunnel wall.
From
2019, construction has begun at Oizumi Junction on the Kan-Etsu Expressway in Nerima Ward, Tokyo
on the north side
.
Mid-last month Excavation in the basement of a residential area with a collapsed road
This time, construction of the "Tokyo Outer Ring Road" is currently underway in the surrounding area, including under the residential area where the road has collapsed.
From Nerima Ward to Setagaya Ward in Tokyo, a road is being constructed underground at a depth of 40 meters or more from the ground surface called "Deep Depth", and north of the Tomei Junction on the Tomei Expressway in Setagaya Ward. It was mid-last month that we started heading towards, passing through Komae City, and reaching the basement of the depressed residential area of Chofu City's roads.
After that, we continued excavation, and after going about 100 meters further, a depression occurred in a residential area on the surface of the earth on the 18th.
What is "deep underground"?
"Deep underground" means underground at a depth of 40 meters or more from the surface of the earth *, and is stipulated by law so that the underground can be used efficiently.
Due to the depth that is not normally considered to be used, the law stipulates that basically no land acquisition or consent from the land owner is required for development.
By using the "deep underground", the Ministry of Land, Infrastructure, Transport and Tourism
can expect to shorten the construction period by an efficient route,
and is safer against earthquakes than shallow underground, which also has the effect of reducing noise and vibration. Is expected.
In addition to the Tokyo Outer Ring Road, the Linear Chuo Shinkansen is also planned to have a tunnel in the "deep underground" section of about 55 km in total in Tokyo, Kanagawa and Aichi prefectures.
* If there is a pile that supports the building, it points to the basement that is 10 meters or more deeper than that.
Expert "I've never heard of a road collapse due to deep excavation"
Regarding this collapse accident, Professor Noriyuki Daiyoshi of Kanto Gakuin University, who specializes in geotechnical engineering, said, "I have never heard of a case where excavation at a depth of 40 meters or more leads to a collapse." Since deep excavation does not affect the ground surface, safety is guaranteed, and there is a history of digging directly under the residential area. We investigated whether this depression is related to the construction, and if it is related If so, it is a new case that has never existed before, and it is necessary to properly verify it. "
He also said, "I don't know the details without verification, but considering that the accident site was excavated about a month ago and it collapsed after a while, it was on the ground surface after excavation. In a near shallow place, it is possible that changes such as movement of groundwater and earth and sand have occurred for some reason, and a cavity has been created over time. In that case, it is possible to consider countermeasures by conducting a new form of underground monitoring. It is necessary to do it. "
In the construction of shallow underground, there was a depression in the past
Underground, which is not deeper than 40 meters from the surface of the earth, which is called the deep underground, has suffered collapse accidents due to tunnel construction.
Of these, in November 2016, the road collapsed on a large scale in front of JR Hakata Station in Fukuoka City, extending approximately 30 meters in length and width and approximately 15 meters in depth.
At that time, there were reports that the collapse occurred because the strength of the bedrock was weaker than expected and the strength of the tunnel was insufficient due to the extension work of the Municipal Subway Nanakuma Line 20 meters underground at the collapse site.
Also, in June, an accident occurred in which two roads directly above the tunnel were sunk one after another due to the tunnel construction of the Sotetsu / Tokyu direct line in Yokohama.
Regarding this accident, a subsequent investigation revealed that the "shield machine" that was excavating a tunnel near 19 meters underground took in excess earth and sand, and as a result, a gap was created underground, which led to the collapse. I am.