Performance of Foundations in the Kanto Plain North of Tokyo during the MW=9.0 Tohoku Earthquake of March 2011-Paper

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The 2011 Mw 9.0 Tohoku earthquake caused severe liquefaction in Fusa and Sawara/Katori, north of Tokyo. Despite being roughly 300 km from the epicenter, the towns experienced strong, prolonged shaking. Young alluvial deposits and poorly compacted hydraulic fills—some created through historical land modification—were especially vulnerable.<br /><br />Field reconnaissance found a marked difference between foundation types. Small buildings on shallow footings or mats often sank or tilted severely; one commercial building on reclaimed fill settled about 1 m. In contrast, buildings supported by deep foundations generally sustained little or no structural damage, even where surrounding ground settled by more than 50 cm. Closely spaced, small-diameter piles extending through the liquefiable layer performed particularly well. However, ground settlement damaged driveways, walkways, and utility services around otherwise sound buildings.<br /><br />The authors used qualitative FLAC numerical analyses to examine a small building on reclaimed pond fill. The model predicted substantial settlement for a shallow-founded structure and much lower structural demand for one supported on small-diameter piles embedded in underlying alluvium. The piles’ flexibility and the ability of liquefied soil to move between them were identified as factors limiting bending demands, particularly where liquefiable deposits were laterally confined.<br /><br />The observations and modeling indicate that modern deep foundations—especially flexible, closely spaced small-diameter piles—can protect buildings from liquefaction-related damage. Shallow foundations remain highly vulnerable, while surrounding ground and lifelines may still suffer significant settlement even when a building itself performs well.

Keywords

Tohoku earthquake

liquefaction

Fusa

Sawara

Katori

deep foundations

shallow foundations

alluvial deposits

small-diameter piles

FLAC numerical analysis