Japan's Defense Ministry on Saturday began ground improvement work on the Oura Bay side of the Henoko coastal area in Okinawa Prefecture, as part of a U.S. base relocation project in the southernmost prefecture.
The work is expected to be difficult due to the unusual depth of the soft ground. It is part of the project to build a replacement facility for the U.S. Marine Corps' Futenma air station in Ginowan, Okinawa.
On Saturday, the Defense Ministry began dropping sand on the seabed using a special work vessel. It plans to drive metal pipes into the seabed and harden the sand inside to create some 71,000 so-called sand piles.
The soft ground is believed to extend as far as 90 meters below the sea surface, while the ground improvement work is planned for depths of up to 70 meters.
The ministry's Okinawa Defense Bureau has said that the work can "sufficiently ensure the stability of structures." Okinawa Gov. Denny Tamaki told reporters at the prefectural government office Friday that he will closely monitor whether stability can be ensured.
The Defense Ministry applied to Okinawa Prefecture for a design change to the base relocation project in 2020, following the discovery of the soft ground. The prefecture rejected the application, but the central government approved the change by proxy last December.
The ministry has since accelerated preparations, including the construction of seawalls on the Oura Bay side starting in August.
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