69. Airports on water, 7th October, 2010
Posted October 7, 2010on:
Airports on water
River deltas are difficult places for map makers. The river builds tem up, the sea wears them down; their outlines are always changing. The changes in china’s pearl river delta, however, bare more dramatic than these natural fluctuations . an island six kilometers long and with a total area of 1248 hectares is being created there. And the civil engineers are as interested in performance as in speed and size this is a bit of the delta that they want to endure.
As check Lap KoK rises however another new Asian island is sinking back into the sea. This is a 520hectare island built in Osaka Bay, Japan that serves as the platform for the new Kansan airport. Check lap KoK was built in a different way, and thus hopes to avoid the same sinking fate.
The usual way to reclaim land is to pile sand rock on the seabed oozes with mud, this is rather like placing a text book on wet sponge: the weight squeezes the settlement is rarely even different parts sink at different rates. So buildings pipes, road and so on tend to buckle and crack. You can engineer around these problems, or you can engineer them out. kansai rook the first approach; check Lap Kok is taking the second. The differences are both political and geological. Kansai was supposed to be built just one kilometer offshore, where the seabed is quite solid. Fishermen protested and the site was shifted a further five kilometers that put it in deeper water (around 20 meters) and above a seabed that consisted of 20 meters of soft alluvial silt and mud dopsits worse below it was a not every firm glacial deposit hundreds of metres thick.
The kansai builders recognized that settlement was inevitable. sand was driven into the seabed to strengthen it before the landfill was piled on top, in an attempt to slow the process; but this is has not been as effective as had been hoped. To cope with settlement, kansai’ s gaint terminal is supported on be individually jacked up, allowing wedges to be added underneath. That is meant to keep the building level but it could be a tricky task conditions are different at chek lap kok there was some land there to begin with, the original little island of chek lap kok and a smaller outcrop called lam chau between them these two outcrops of hard weathered granite make up a quarter of the new island’s there was a layer of soft mud 27 meters thick in places .
According to Frans Uiterwijk, a Dutchman who is the project’s reclamation director ,it would have been possible to leave this mud below the reclaimed land, and to deal with the resulting settlement by the kansai method. But the consortium that won the contract for the island opted for a more aggressive approach.
Assembled the world’s largest fleet of dredgres which sucked up 150m cubic meters of clay and mud and dumped it in deeper waters at the same time, sand was dredged from the waters and piled on top of the layers of stiff clay that the massive dredging had laid bare. Nore was the sand the only thing used the original granite island which had hills up to 120 meters high was drilled and blasted into boulders no bigger than two metres in diameter this provided 70m cubic metres of granite to add to the island’s foundations. Because the heap of boulders does not fill the space perfectly this represents cubic meters of landfill. Most of the rock will become the foundations for the airport’s runway and its taxiways the
sand dredged from the waters will also be used to provide a two meter capping layer over the granite platform this makes it easier for utilities to dig trenches granite is unyielding stuff most of the terminal buildings will be placed above the site of the existing island only a limited amount of pile driving is needed to support building foundations above softer areas the completed island will be six to seven meters above sea level in all 350cm cubic meters of material will have been moved and much of it like the overloads has to be moved several times before reaching its final resting place. For example there has to be a motorway capable of carrying 150 tonne dump truck and there has to be raised area for the 150000 construction workers these are temporary they will be removed when the airport is finished.
The airport though is here to stay to protect it the new coastline is begin bolstered with a formidable twelve kilometers of sea defences the brunt of a typhoon will be deflected by the neighbouring island
Of lantau the sea wall should guard against the rest gentler but more persistent bad weather the downpours of the summer monsoon is also begin taken into account a mat like material called geotextile is being laid across the island to separate the rock and sand layers that will stop sans particles from begine washed into the rock voids and so ausing further settlement this island is begin built never to be sunk.