so is our reclaimed land sinking?
Tremors and Reclaimed Land
Reuters
Mar 10, 2007
One Raffles Quay, the newest office block in Singapores financial
district, overlooks a vast swathe of reclaimed land on which a huge
casino, a swanky apartment block and a new financial centre are
rising up.
On Tuesday morning, as One Raffles Quay was swaying, rocked by a
6.3 magnitude earthquake in Sumatra, Indonesia, 420km west of
Singapore, some of its occupants could not help but wonder: how
quake-resistant are buildings on reclaimed land?
Nearly 20 per cent of land-scarce Singapores surface area is
reclaimed from the sea, and Singapore has scores of tower blocks,
hotels, factories and petrochemical plants on reclaimed land. In
the coming years the city-state will develop a second financial
centre, all on reclaimed land in the Marina Bay area.
So, is it safe?
Engineers say that because reclaimed land is created by dumping
sand into bodies of water, buildings rock more violently during
tremors, although that does not mean they are unstable.
Reclaimed land is made up of sea sand, so buildings will be shaken
up more violently during earthquakes as compared to those on
non-reclaimed land, which is solid and will not be liquefied by the
shake, said Fan Sau Cheong, an engineering professor at
Singapores Nanyang Technological University.
He said that buildings on reclaimed land may shake two to three
times more than those on natural land during earthquakes because
sand in reclaimed land slides like liquid when saturated with
water, in a process called liquefaction.
On Tuesday, about 150 buildings in Singapore were rattled by the
quake and hundreds of people in the financial district fled their
offices. No buildings were damaged and nobody was hurt.
Panicking
Blinds were shaking and the secretaries started panicking, said
an office worker at One Marina Boulevard, a tower block next to One
Raffles Quay.
Then some people started saying Oh no! And we are on reclaimed
land! Its just this instinctive fear that there are more risks
with reclaimed land, she told Reuters.
Singapores Building and Construction Authority denied that
buildings on reclaimed land are more vulnerable to tremors than
those on natural land, citing strong building foundations that can
withstand tremors from distant earthquakes.
Unlike buildings in earthquake-prone Japan and Taiwan, Singapore
buildings are not designed to be quake-proof, as Singapore does not
sit on any major geological fault lines.
But since quakes in Indonesia are often felt here, the joints
connecting the columns in many tall buildings should be connected
more flexibly, to allow them to better absorb tremors, Fan
said.
To ensure that a plot of reclaimed land will be stable enough to
hold buildings, Singapore lets the land lay fallow for about 20
years to allow the sand to settle.
Singapore is not the only country building on reclaimed land.
Macau has reclaimed land to erect more casinos and hotels, while
Dubai has spent hundreds of millions of dollars creating a
palm-shaped resort island off the coast of the Gulf emirate.
Engineers say that reclaimed land is always prone to sinking due to
the difficulties in compacting the sand and draining the water
trapped inside the reclaimed plot, which causes reclaimed land to
subside more easily.
Japans Kansai International Airport, the worlds first airport
built on reclaimed land, has sunk more than 11.5 metres since
construction began in 1987.
However, buildings on reclaimed land will not sink if they are
supported by steel or concrete columns that are hammered all the
way into the seabed, although the streets circling the buildings
may sink alongside the drooping land, engineers say.
The building will not be floating on reclaimed soil, said Lee
Siew Eang, a building professor at the National University of
Singapore.
Reuters
