A NEW suspended structure at Madeira's Funchal airport added nearly a kilometre to the length of the runway when it opened to traffic last month.
Partly elevated 60m above sea level, it enables the airport to accommodate jumbo jets and nearly doubles its capacity to 3. 5 million passengers per year.
Madeira is a volcanic island that rises steeply from the seabed to more than 1800m, with few flat areas of land. The original runway was built across the neck of a peninsula, cantilevering over the water at each end.
Taking the new runway across the adjoining bay to the next peninsula made it possible to increase the length to 2. 8km. This also allowed realignment of the runway by 3degrees to improve the flight approach and enabled the airport to continue operating throughout construction.
The new 178m wide structure comprises prestressed concrete slabs and transverse beams supported on 176 columns of 3m diameter at 32m centres, the tallest measuring nearly 46m from base to soffit. The columns are founded on more than 700 bored piles - mostly 1. 5m in diameter and up to 50m deep - totalling 20 000m in installed length.
To facilitate construction, land was reclaimed from the sea to a depth of 20m, providing a working platform clear of the tides.
This reclamation is protected by a berm breakwater built from rock excavated as part of the earthworks for the runway.
British consultant Mott MacDonald focused on design appraisal and technical assistance working as part of a consortium (led by Consulgal of Portugal and including O'Brien Kreitzberg and Prima) which was responsible for project managing and supervising construction.
The new runway has to cater for seismic effects as well as the major loading induced by aircraft. Detailed designs were prepared for joint venture main contractor Novapista SA by Segadaes Tavares & Associates and Consulmar.
Independent checking was carried out by the consultancy consortium as part of its technical assistance role covering all aspects of structural, geotechnical and marine engineering. Mott MacDonald provided specialists on site to assist with piling, prestressing, marine works and hydraulic testing.