About the depression of the ground surface near the construction site of the Tokyo outer ring road (Kan-etsu-Tomei) [6th report]

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Regarding the ground surface depression that occurred near the construction site of the main line tunnel (southbound) on the Tokyo Outer Ring Road (Kan-etsu-Tomei), we confirmed a cavity in the ground when we conducted a ground survey around the depression.

1. 1. place

Near 2-chome, Higashi Tsutsujigaoka, Chofu-shi, Tokyo
(Geological survey site on the north side of the ground surface depression that occurred on October 18)

2. Cavity situation

Cavity depth from the ground surface is about 5m, width is about 4m x length is about 30m, thickness is about 3m
(Refer to the attached sheet [PDF: 696KB])​

3. 3. Future response

With safety and security as our top priority, we explain this event to neighboring residents and take necessary measures.
In addition, experts have commented that due to the condition and size of the cavity, it does not immediately cause deformation on the ground surface and does not require urgent action, but it is desirable to fill the cavity early. ..

In response to this, the causal relationship with the tunnel construction is unknown, but the following measures will be taken.

• Filling the confirmed cavities will be carried out promptly.
• In addition, constant observation of ground surface displacement is continuing. No anomalies have been confirmed at this time.
• We are planning to hold a committee of experts on this matter on November 5th tomorrow.