World's Largest Caisson

Maeda, Kunio; Shiraishi, Shunta; ,

World's Largest Caisson

by Kunio Maeda, Dir. of Tokyo Waterfront Projects; Metropolitan Expressway Public Corporation, Tokyo, Japan,
Shunta Shiraishi, (F.ASCE), Chairman; Shiraishi Corporation, Tokyo, Japan,

Serial Information: Civil Engineering—ASCE, 1990, Vol. 60, Issue 8, Pg. 47-49

Document Type: Feature article

Abstract:

The world's largest caisson (210,000 cy) forms the offshore cable anchorage for the 1,870 ft main span Tokyo Harbor Bridge. The bridge carries Metropolitan Expressway Route No. 12, four additional lanes of highway, two urban-transit tracks and sidewalks linking downtown Tokyo with the future offshore Sub-City Center. Workers dug out the first 10 ft of soil; afterwards, power shovels did nearly 90% of the remaining excavation. The shovels were suspended from rails attached to the ceiling slab of the working chamber and had telescoping booms. The shovels deposited excavated earth in quick soil loaders, which discharged into earth buckets when full. When working-chamber air pressure reached 38.4 psi the shovels were converted to unmanned operation; the operators worked the shovels from atmospheric capsules lowered into the working chamber. Six deep wells were used to pump out ground water and keep working-chamber air pressure at levels allowing their operators to work reasonable shift lengths. When excavation reached the stiff hardpan beneath the clayey soils, jib cutters (like giant chainsaws) and twin headers (wheel cutters attached to the front of a caisson shovel's telescopic boom) cut through it, the jib cutters along the cutting edges of the caisson and the twin headers toward the center. Work was completed in December 1989.

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