Settlement of the Kansai International Airport Islands

The Kansai International Airport was constructed in Osaka Bay in 18- to 20-m-deep seawater to avoid noise pollution and land acquisition disputes. Construction of the 511-ha Island I began in 1987 and Runway I began operation in 1994. Construction of the 545-ha Island II began in 1999, and Runway II began operation in 2007. Using more than 2.2 million vertical sand drains fully penetrating into the 17.3- to 24.1-m-thick Holocene clay layer and 430 million cubic meters of fill material, the project is viewed as an engineering marvel. On the basis of a detailed review of the geology of Osaka Bay, construction of the Airport Islands, and the permeability and compressibility of the Holocene and Pleistocene subseabed deposits that reached a depth of 400 m below the seafloor at the Kansai Airport site, settlement analyses were conducted assuming the uniqueness of end-of-primary void ratio-effective vertical stress relationship and the C_α/C_c law of compressibility. Airport Island I has already settled below the 4-m above sea level surface elevation required by the design specification, and the surface elevation of Island II is predicted to be 4 m above sea level by 2023-2036. Airport Islands I and II will be at sea level, respectively, by 2067 or sooner and by 2058-2100. By the end of the 21st century, Island I and Island II are predicted to settle, respectively, 17.6 and 24.4 m.