Ground Improvement Work for Air Station Set to Start in Henoko; Issues of Spiraling Costs, Opposition in Okinawa Remain

Yomiuri Shimbun file photo
A coastal area of the Henoko district in Nago, Okinawa Prefecture, undergoing land reclamation is seen in October 2022.

The Defense Ministry is set to start ground improvement work in the Henoko coastal area of Nago, Okinawa Prefecture, where the functions of the U.S. Futenma Air Station in Ginowan in the prefecture are to be relocated. This work follows a high court ruling that allows the central government to approve design changes for the relocation, acting in place of the Okinawa prefectural government.

As part of the design changes, the ground improvement work entails driving about 70,000 piles into the seabed to enhance its stability. However, the Okinawa prefectural government is prepared to engage in further legal battles, presenting challenges that may have to be addressed before the relocation process — which is expected to take about 12 years — can be completed.

“This is a milestone toward the full-scale return of the Futenma Air Station,” Defense Minister Minoru Kihara told reporters at the Defense Ministry on Thursday, while expressing his intention to steadily proceed with the improvement work.

Often referred to as “the most dangerous base in the world,” there have been repeated calls to mitigate the risks associated with the air station. Meanwhile, the importance of Okinawa, where U.S. Marines are stationed, is increasing due to Japan’s deteriorating security environment. Therefore, the relocation of Futenma to Henoko is “a realistic option,” as a senior government official said.

The Defense Ministry is set to begin the ground improvement work as early as mid-January on the planned reclamation area on the Oura Bay side of the U.S. military’s Camp Schwab, where soft ground was found. Three years and eight months have passed since the central government applied to the Okinawa prefectural government regarding the ground improvement work.

“We’re finally at the starting line,” a senior Defense Ministry official said.

The Yomiuri Shimbun

The ground improvement work will involve building a seawall first, followed by driving steel pipes into the soft seabed and pouring sand into them using a work boat. This will create about 71,000 sand piles to stabilize the soft seabed. Afterward, sand and soil will be placed over the area. The entire ground improvement process alone is estimated to take about four years and one month.

The method of work has been employed in many past land reclamation projects, including those for Haneda and Kansai International airports, where the number of sand piles used exceeds those planned for the Henoko area. However, the Henoko area presents a unique challenge with its thick layer of soft seabed, requiring sand piles to be driven down to up to about 70 meters below sea level. This makes the project unprecedented and one of the most difficult of its kind in Japan. Consequently, should new problems emerge during the work, the central government might need to modify the project design. Furthermore, the suspension of the work may happen if the Okinawa prefectural government seeks judicial intervention again.

The costs related to the work, initially estimated at more than ¥350 billion, have already ballooned to about ¥930 billion because of the prolonged construction period. Considering the impact of high prices and other factors, a senior Defense Ministry officials has said that a review of the costs will eventually be necessary.