The controversy over whether 'Gadeokdo' is suitable as a site for a new airport has been ongoing since 20 years ago. Although the atmosphere of the project is being promoted as promised by President Lee Jae-myung, concerns from the aviation and construction industries regarding 'safety and economic viability' remain significant. Attention is focused on the intrinsic limitations of Gadeokdo New Airport and the background of Hyundai E&C, the consortium leader, declaring its non-participation. ChosunBiz aims to discuss technical safety issues, such as construction methods and uneven subsidence, in depth prior to re-tendering the 'Gadeokdo New Airport site preparation project.'<editor's note>
Expectations for the rosy future of Gadeokdo New Airport construction stem from the success of Kansai International Airport in Japan. Kansai International Airport is the world's first artificial island airport, built as Japan's largest and most significant civil engineering project. It has been selected as one of the 'world's top 10 architectural structures.' However, excessive subsidence beyond expectations has turned it into a 'burden' for the Japanese government, requiring significant maintenance expenses each year.
Recently, there has been an analysis suggesting that 'part of Kansai International Airport will be submerged in water in 30 years.' Despite the construction expense of 30 trillion won and the deployment of cutting-edge construction methods, its limitations are becoming evident over time.
According to a report by ChosunBiz on the 2nd, repair work is currently underway at Kansai International Airport to add coastal levees and embankments. This is because one of the two artificial islands supporting Kansai International Airport has sunk nearly 18 meters. This island was built on a 20-meter thick soft ground and has 2.2 million vertical drainage pipes installed, but the clay layer beneath is gradually compressing. The current lowest point of the airport site is known to be 2 meters above sea level. The expense for this project is $150 million, which is about 200 billion won.
There are also other ongoing projects at Kansai International Airport to address subsidence. These include waterproof wall construction, groundwater and drainage system maintenance, and jack-up projects due to uneven subsidence. The jack-up project works to correct the horizontal alignment of 900 columns in Terminal 1 of Kansai International Airport. The degree of subsidence varies by column, and plates are inserted to level them.
The process involves inserting metal plates at the bottom of the columns to adjust their height, much like propping up a wobbly table with paper under one of its legs. Kansai International Airport has disclosed detailed information about the jack-up system on its official website. According to the Japan Mainichi Shimbun, the costs of the jack-up project are undisclosed and it is performed periodically every few years.
Foreign media outlets have been focusing on the subsidence at Kansai International Airport recently. According to a report by the British daily 'Independent' on the 23rd of last month (local time), if the current rate of subsidence continues, part of the airport could be below sea level by 2056. This is because the amount of fill material was determined based on the estimated subsidence for 50 years after the airport opened.
Kansai International Airport opened in 1994. This analysis is based on the premise that maintenance work would continue at the current level. Asian media, including Singapore's 'Straits Times' and China's 'South China Morning Post (SCMP)', have also followed up on this report.
When Kansai International Airport was constructed, it was anticipated that it would settle 11.5 meters over 50 years, which was the basis for deciding the amount of fill material. However, after only six years of operation, it subsided by 11 meters. This is attributed to a combination of factors that were difficult to predict beforehand, including the weight of accumulated soil, the load exerted by large aircraft taking off and landing, rising sea levels, and irregular ground movements. Due to overall subsidence, Kansai International Airport was closed for 15 days when Typhoon Jebi struck Japan in September 2018, as the runway was submerged.
With enormous sums being invested in maintenance expenses each year, Kansai International Airport has become the most expensive airport in the world for aircraft landing fees. Consequently, airlines worldwide have naturally reduced their operations at Kansai International Airport. Last year, the number of passengers utilizing Kansai International Airport was 31.8 million, less than half of Incheon International Airport's 70.7 million. The airport's operating conditions have also deteriorated sharply. As the liabilities of Kansai International Airport increased, the Japanese government merged it with the nearby Itami Airport in 2011 and established a holding company to operate it. Then, in 2016, it sold the operating rights to the private sector. Kansai International Airport has been identified as a representative case where excessive construction costs and maintenance expenses due to subsidence have led to a decline in airport competitiveness.
The case of Kansai International Airport serves as a point of reference before the site preparation work for Gadeokdo New Airport. Gadeokdo New Airport is likely to have more variables than Kansai International Airport, which is located in the inner Seto Inland Sea. The main reason why Gadeokdo and Miryang in Gyeongnam, which were competing as candidate locations in 2011, were both eliminated was due to 'unfavorable topographical conditions.' At that time, Miryang received a score of 39.9 out of 100, while Gadeokdo scored 38.3. The then-chairperson, the late Park Chang-ho, a professor of civil engineering at Seoul National University, stated, 'Both candidate sites are unsuitable as airport locations due to environmental damage and excessive construction costs from the unfavorable terrain, with their economic viability being insufficient.'
The advanced construction methods to be applied to the site preparation for Gadeokdo New Airport also involve significant uncertainties. The vertical drainage (PBD·Plastic Board Drain) method, widely used for soft ground improvement, has not been employed in maritime contexts in South Korea, except for the Busan New Port project. It involves inserting plastic boards into the clay layer of the soft ground to facilitate drainage. While Busan New Port is in the inner sea, Gadeokdo New Airport is located in the outer sea, making its environment different. The soft ground beneath Gadeokdo New Airport is up to 60 meters deep. Concerns about environmental pollution have recently been raised regarding this method, suggesting the use of biodegradable eco-friendly plastic boards.
A civil engineering official from a large construction company stated, 'This method has not been used in large-scale maritime projects overseas,' adding, 'Given that it is an unverified method in major projects, there is a significant possibility of ground subsidence after application.'
Concerns have been raised that there may be difficulties in equipment procurement for the deep cement mixing (DCM) method aimed at preventing uneven subsidence. This method is commonly referred to as underwater concrete work, whereby a mixture of cement and water (slurry) is injected under low pressure into the soft ground, leading to a reaction with the soil to replace the soft ground with concrete mass.
This method can be used to improve the ground connected to the runway. Although it has been applied in the construction of Ulleung Airport, Gadeokdo New Airport requires the construction of a large runway, which poses limitations solely with domestic equipment. The construction industry expects that DCM-specific vessels will not be secured until the second half of next year.
Meanwhile, the Ministry of Land, Infrastructure and Transport mentions an estimated project cost of about 13 trillion won for Gadeokdo New Airport, but there are analyses suggesting that it will actually exceed 16 trillion won. According to a report titled 'Review of the Feasibility of the Gadeokdo New Airport Construction Project' published by the Korea Development Institute (KDI) in 2023, the total project cost is estimated at 16.6437 trillion won, considering the rise in basic unit prices, insufficient project plans, design errors, and omitted expenses. KDI also warned of the overestimation of aviation demand and future cargo demand.
Professor Jeong Chung-ki from the Department of Civil and Environmental Engineering at Seoul National University (former president of the Korean Society of Civil Engineers) noted, 'Gadeokdo New Airport is located in the outer sea, where waves are strong, and the overall construction, including the installation of breakwaters, is expected to be challenging,' adding, 'For the PBD method, it will need to be drilled to 100 meters on a shaking ship.' He continued, 'Considering the geographical conditions of Gadeokdo, making definitive estimates of construction costs and duration will be quite difficult. Experts need to be allowed to make careful judgments.'