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STORIES OF THE SWAMP

Dutch-style polders and thousands of wick drains feature on Bangkok's second international airport, which is finally nearing completion after a chequered history. Adrian Greeman reports.

It began nearly 20 years ago with cobras in the spoil heaps and dragon lizards warming themselves on Tarmac site roads, then became an imported Dutch world of polders and canals; now it is a Dante's inferno of heavy welding and steel fi xing. Sparks and smoke belch from a row of fiery furnaces producing asphalt for the runway.

Amid tropical heat and monsoon rains, Thailand's Suvarnabhum Airport, just south of Bangkok, is fi nally taking shape. It might even get somewhere near a much heralded September opening this year, at least with a token plane-landing and formal ceremony, though there will still be a few months of work to achieve final international approvals.

The project nearly did not happen at all. Despite the Thai government's foresight in acquiring land south of Bangkok 30 years ago - no small thing in a country without compulsory purchase powers - and the planning, architecture and structural design work that took place in the early 1990s, everything hit the buffers in 1997 as the Asian currencies collapsed.

Suddenly nothing moved on Bangkok construction sites. At the airport, ground clearance and surcharging continued for a while but eventually this stopped too.

Then, hesitantly, things began to pick up, not least the airport, which has been given a Baht73bn (£1.06bn) injection by the Japan Bank for International Cooperation, 60% of the £1.67bn total project cost.

Another £400M of private investment is being made.

Work restarted in 2002 with a Japanese-dominated construction project direction team led by Pacific Consultants International replacing the original group of Louis Berger and NACO.

But the original US architectural design by Murphy/Jahn and Tams Consultants (part of the EarthTech group since 2002) with local firm Act Consultants Company is still being used and most of the design and supervision teams who worked on the terminal and pavements are still in place.

Chief among them is the TCS consortium led by Germany's Dorsch Consult with Scott Wilson, Japan Airlines' JAL Aviation Consulting and 10 Thai consultants.

The site is dominated by the huge terminal building and its tubular concourse extensions, stretching outwards in a right-angled H-shape plan across the airfi ld. But the immense paving operation is equally significant.

Contractor IOT, made up of Italian-Thai Development with Takenaka and Obayashi from Japan, has eight concrete batching plants and fi ve large asphalt furnaces working continuously to provide the material for 1m. m 2 of pavement quality concrete and asphalt runways and taxiways totalling 2M. m 2.Work on the £200M contract includes construction of an 820m long, 54m wide concrete cut and cover tunnel to accommodate baggage handling and a people mover to service a future satellite terminal when the airport expands from an initial 45M passenger annual capacity to 100M.

Much of the ground clearance was done in the 1990s, transforming a 'cobra swamp' into usable space.

Scott Wilson's Lauri van Run says this included creating an embankment around the airfi eld and a network of 40km of canals within it to stabilise the water table, using classic Netherlands techniques.

The fi rm leads the paving supervision group of fi ve consultants; the others are Norway's Norconsult and three local firms.

'The drainage also holds back up to seven days of tropical rainfall inside the airport to protect surrounding villages from flooding, ' van Run adds. 'The whole area is downstream of Bangkok and provides a flood holding area.' On Bangkok's notorious 'toothpaste', 12m-20m thick soft marine clay with 80% to 120% water content, potential settlement of the runways and taxiways is a huge problem.

Lime cement columns, a reinforced concrete piled slab or lightweight material replacement were assessed as solutions, but in the end the choice was thousands of prefabricated vertical drains with surcharge loading. Full-scale field trials of the technique were positive.

The fi st step was to regrade the improvement area and place a 1m thick layer of sand. The drains were installed to 11m depth at 1m intervals and another 0.5m of sand placed on top, before the surcharge stone was placed. Ground improvement helped induce an estimated 1.5m to 1.8m settlement.

Van Run says careful control of the pavement construction is crucial. 'Aircraft don't like bumps and humps and you have to achieve tolerances of not more than 3mm in any 3m.'

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