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Confidence building

KOREA; The South Korean economy may still be on shaky legs but the country's construction industry is building for a booming future. Neil Doyle reports from the start of Seoul's enormous new airport which will be able to handle 100M passengers a year.

Inchon International Airport is construction on a gargantuan scale. The $7bn (£4.4bn) development is being built on reclaimed land offshore between two islands 52km to the west of the South Korean capital Seoul. It is designed to relieve the existing Kimpo International Airport, which reached saturation point in 1997.

The development is so large that the Inchon International Airport Corporation prefers to call it a 'pentaport', to include all five functions of the development which will also boast a leisure resort, an intermodal transport hub, a business district, and a state-of-the-art sea port providing connections to major ports in China.

Intended as the new gateway to east Asia, the airport will cater for the rapid growth in air traffic in the Asia Pacific region, which is expected to account for 49.8% of world air traffic by 2010. It will also be ready for the next generation of large supersonic aircraft and will be capable of handling 100M passengers a year by 2020.

'We studied 22 locations in 1990 and the criteria was that the airport needed to be within a 100km radius of Seoul,' says Dr Sang-Ho Lee, executive director of the construction management division of Inchon International Airport Corporation. 'We focused on three locations and we decided finally on Inchon. This site is very good because it is just over 50km from the centre of Seoul and there are no noise problems. The land is tidal so the water depth is low which meant the cost of reclamation was also very low - one sixth that of Kansai airport in Japan.'

'We spent six or seven months considering the best method for soil stabilisation. There is a small island nearby, which was 130m at its highest point. We have cut it down to 45m for the safe operation of aircraft and we used the excavated rock for the reclamation of the airport site, and for making concrete,' adds Dr Lee.

The 5,617ha site has been formed by linking Youngjong and Yongyu islands using 17.3km of dykes and 180M.m3 of earth to an average depth of 5m. Several techniques have been used to stabilise the soft soil with sand drains used in most locations.

A total of 280,000 vertical sand pipes have been driven into the soil, typically at 3m centres, to a depth of 10m to drain any remaining water and compact the soil. The soil is expected to settle by an average of 500mm in the short term and by a further 20mm over the next 20 years. The site also has 100km of underground stormwater drainage channels, formed with precast concrete units produced by a factory on site.

Further compaction work using 10t hammer equipment was undertaken in the runway areas, to ensure they have the ability to support the 429t maximum take off weight of future 'superjumbo' airliners. A 1.05m thick concrete and asphalt pavement is designed to cope with 1,500 flights daily. Four 3,750m-long runways are being constructed and there is room for a fifth to accommodate further growth in demand.

The airport complex is centred on two passenger terminals and four remote concourses with a total floor space of 875,000m2, and a futuristic transportation centre covering 250,000m2 is located between the terminals. Terminal 1 will be the largest structure in Korea at 1,066m long, 145m wide, and 33m high. The curved steel and glass edifice is founded on 15,000 steel piles driven down to an average of 43m, and designed to withstand an earthquake of up to magnitude seven, although seismic activity in Korea is minimal.

'In 1991 we had an international competition for the design of the passenger terminals won by a consortium comprising KACI, Baum, Heerim, Junglim and Wondoshi,' explains Dr Lee. 'We also had a competition for design of the transportation centre which was won by the British architect Terry Farrell & Partners.'

Engineers for the projects are Junglim, KACI, Heerim, Samwoo and Nara.

The steel structural framing is designed for a maximum span of 18m and topped with a shell roof structure that spans 88m, with the roof of the attached concourse supported by masts and cables. The roof trusses are used as an architectural feature, emphasised by long bands of fritted glass skylights, complimenting the slanted glass curtain wall facade.

A consortium including Hanjin, Samsung, Daewoo, and Fluor Daniel is undertaking construction of the structural elements of the airport. Work started in November 1992 and the first phase, covering two runways, Terminal 1, cargo terminals, a communication centre, maintenance hangers, 50 support buildings and the transportation centre, is due for completion by the end of next year. The international business centre, a support complex, and the 40.2km Airport Expressway road link are also under construction. The first phase represents 40% of the development, and construction of the later phases will continue until 2020 according to future growth in air traffic.

As well as the Airport Expressway, a 61.5km long double-track railway is being constructed to connect the airport with Seoul station. The $670M (£419M) Yongjong Grand Bridge, a 4.4km-long double deck Warren Truss bridge with a suspension section as its focus, will be the main link between the airport and the mainland. The bridge will carry a six-line expressway on the 45m wide upper deck and a four-lane road and a double railway track on the 35m wide lower level 11m below. The work is split between a number of contractors including Samsung, which is building the suspension section (NCE last week).

'The construction techniques for Youngjong bridge are very complex, so we extended the construction period. Samsung Construction started to seriously rethink the construction methods and solved some technical difficulties,' says Dr Lee.

The suspension structure is claimed to be the first double deck self- anchored suspension bridge in the world.

Pneumatic steel caissons were used to construct the foundations of the main towers and excavations were carried out by remotely controlled machinery - a first for Korea. The rest of the bridge substructure is founded on cast-in-situ concrete piles. Two more bridges and a canal are planned to provide more links to the mainland in later phases of the development.

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