Tremors and Reclaimed Land
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so is our reclaimed land sinking?
Tremors and Reclaimed Land
Reuters
Mar 10, 2007
One Raffles Quay, the newest office block in SingaporeÂ’s 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 SingaporeÂ’s 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 Singapore’s 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!’ It’s just this instinctive fear that there are more risks with reclaimed land,” she told Reuters.
SingaporeÂ’s 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.
JapanÂ’s Kansai International Airport, the worldÂ’s 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 -
Reclaiming land is machiam like buy a PS2. Very expensive when buying it and watching it detroiate as times goes by. Then you start to count how much $ per year to pay for that particular thing?
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Well, we could promote the IR as an underwater attraction should that happen.
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Reclaiming land... it's like sandcastle building on a large scale... Hopefully our buildings last longer than those on the beach.
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Humans bullshit. Tremors don't.
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I want to point out the fact that Indonesia's earthquake's epicentre, is shifting closer and closer to Singapore.
If it gets any closer within this decade, we won't just be experiencing tremors - our lives may become shaken if not shooked!
As such, I can't help wondering, how any of our high-rise buildings and HDB dwellings can withstand the first initial quake in Singapore since none were built with earthquakes in mind???
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Earthquake Liquefaction
Earthquake liquefaction, often referred to simply as liquefaction, is the process by which saturated, non-cohesive soil (sand and silt) loses shear strength during seismic shaking and behaves like a liquid, rather than a solid. The effect on structures and buildings can be devastating, and is a major contributor to urban seismic risk.
Liquefaction occurs when a saturated sand formation is subject to cyclic shaking. The shaking causes increased pore water pressure which reduces the effective stress, and therefore reduces the shear strength of the sand. Soils most prone to liquefaction are loose sands between layers of lower permeability soil that prevent rapid dissipation of cyclic pore pressures. As seen in the figure, uniform sand grains can be packed either in a loose or a compact (dense) formation. Loose sand has usually been deposited gently underwater, either naturally, or sluiced into what is called hydraulic fill. The loose grains can support considerable weight, as they are in contact with each other in a statically stable formation.
Once strong earthquake shaking begins, the grains are separated by high pore water pressure and are no longer resting on each other. Eventually, the grains will settle into a more compact arrangement. However, this transition is not immediate, and requires excess water to leave the formation. For a short period of time, depending how long it takes for the water to drain from the formation, the grains float in a liquid slurry. The excess water is squeezed out which causes the quicksand condition at the surface. If there is a dry soil crust or impermeable cap, the excess water will sometimes come to the surface through cracks in the confining layer, bringing liquefied sand with it, creating sand boils, colloquially called "sand volcanos".
Soil liquefaction can cause damage to structures in several ways. Buildings whose foundations bear directly on sand which liquefies will experience a sudden loss of support, which will result in drastic and irregular settlement of the building. Liquefaction causes irregular settlements in the area liquefied, which can damage buildings and break underground utility lines where the differential settlements are large. Sand boils can erupt into buildings through utility openings, and may allow water to damage the structure or electrical systems. Soil liquefaction can also cause slope failures. Areas of land reclamation are often prone to liquefaction because many are reclaimed with hydraulic fill, and are often underlain by soft soils which can amplify earthquake shaking. Soil liquefaction was a major factor in the destruction in San Francisco's Marina District during the 1989 Loma Prieta earthquake.
Study of past liquefaction events in geologic formations can provide information about the strength of prehistoric earthquakes, a vital component of paleoseismology.
Liquefaction primarily occurs in sands, but there are formations of quick clay, which can fail in a very similar way.
Mitigating potential damage from liquefaction is part of the field of geotechnical engineering. -
those gambling at the casinos are as good as idiots or addicted ...Originally posted by charlize:Well, we could promote the IR as an underwater attraction should that happen.