Due to emerging a series of sinkholes in Chofu City, western Tokyo, a report blamed tunneling works in this area last week.
According to East Nippon Expressway Co. expert panel report, which had been determined by Japan’s influential Asahi Shinbun for surveying the cause of this problem, tunneling on Tokyo’s external ring road was the reason of the cave-ins and huge cavities. The sinkholes commenced on 18 October 2020, when a 5m wide and 5m deep hole revealed in the middle of the road in a Chofu City local area.
Conforming expert’s statement after digging more than 40 m beneath the ground on the Tokyo Gaikan Expressway, the tunnel boring machine faced difficulties mining the bedrock. Creating cavities in the crest area of the tunnel was due to using chemical facilitators in the work. Moreover, according to the presented studies, the sinkholes revealed in the areas of made-up ground which were majorly destabilized by a layer of sand and gravel.
The Central Japan Railway Co.’s Linear Chuo Shinkansen project, can be affected significantly from the results of this project’s reports, because the location and depth of the tunnels are similar in both of the works.
In accordance to Shinya Inazumi, a professor of geotechnical engineering at Shibaura Institute of Technology’s explanation, working at depths of above 40m vouched no safety and requires a diverse approach to that of traditional civil engineering.