How Sand Compaction Piles Saved Tokyo Disneyland From Earthquake Damage
When the March 11th earthquake struck Japan, I was at Tokyo Disneyland. Inside the park, I saw absolutely no damage from the quake, but when I exited Disney and walked around the streets of Urayasu City, I saw quite a bit of cracked and damaged streets. The above photo, which I snapped in front of Maihama Station, demonstrates the effects of soil liquefaction:
The liquefaction left houses and power poles tilting in many areas.
Liquefaction occurs when saturated sandy ground, such as that found in reclaimed land and marshes, is loosened by a strong earthquake. The unconsolidated sand becomes like muddy water. This muddy water gushes up through cracks and opening in sidewalks and roads, and then drains away to leave the sand on the ground.
The latest earthquake caused ground subsidence of up to 50 centimeters, which destroyed underground water and sewerage pipes.
Reclaimed land usually stabilizes with time. Some areas along Tokyo Bay were reclaimed during the Edo period (1603-1867) and before World War II. However, the areas hit hardest by liquefaction during the March 11 earthquake had been reclaimed after the war with sediment taken from the seabed. In those areas, digging down a few meters will reveal a saturated sandy layer.
The Tokyo Disney Resort was also built on recently reclaimed land. Why did it not suffer from liquefaction?
The answer, as explained in this FTV news video, is sand compaction piling:
The sand compaction pile method, developed in Japan about 50 years ago, uses steel pipes to insert large amounts of compacted sand into the ground, strengthening relatively weak soil against liquefaction.
Sand compaction piles were placed under the Tokyo Disney Resort and Haneda Airport, and both survived the earthquake without suffering significant liquefaction damage.
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