Current Practice Concerning Drilled Shafts to Support Buildings in Japan-Paper

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The paper reviews current practices and technological developments in drilled-shaft foundations for buildings in Japan. Building and civil-engineering projects follow different design codes, which use different methods for calculating pile bearing resistance. Unlike civil-engineering practice, building foundations commonly use enlarged-bottom shafts and may support each column on a single pile.<br /><br />Earth-drill, reverse-circulation, and all-casing methods are used, with the earth-drill method dominant in building construction. Typical shaft diameters are 1.0–1.5 m or 2.6–3.0 m; about half of building shafts include an enlarged base. Since restrictions on enlarged-base geometry were removed in 2002, designs have expanded to larger bases, higher enlargement ratios, and stronger concrete. The paper describes the new ACE method, which uses hydraulically operated blades to form a cone-shaped enlarged base.<br /><br />To meet seismic demands, Japanese developers have also created shafts with enlarged nodules at multiple points along the shaft. These increase frictional resistance and help resist uplift, which may otherwise require impractically long or large-diameter piles. The Me-A method combines such nodules with an enlarged tip.<br /><br />A case study describes a 23-storey office building above a station, founded on deep shafts extending through soft alluvial deposits to a bearing layer at about 45 m depth. Earthquake loading created substantial compression and uplift forces. Enlarged-base shafts provided the required compressive capacity, while Me-A nodules added pull-out resistance. The design kept the uplift demand-to-capacity ratio at or below 0.85.<br /><br />The paper concludes that combining enlarged bases and multi-stage nodules can provide an economical foundation solution for high-rise buildings where conventional shaft friction alone is insufficient.

Keywords

drilled-shaft foundations

Japan

enlarged-base shafts

earth-drill method

pile bearing resistance

building foundations

seismic design

uplift resistance

ACE method

Me-A method