Abstract
The substructure of YOKOHAMA Bay Bridge is multi-column foundation; for the tower foundation, nine piles are grouped and the tops of each pile are imbedded in a footing. Each pile is constructed by sinking a 10m out dia, open caisson made of reinforced concrete. Those caissons are penetrated about 20m in depth into the soft mud stone bed. To penetrate such big caissons deep into a bearing hardpan, it is necessary to excavate and remove the material under caissons' cutting edge. We have already developed a swing boom type under-water drilling system that can excavate and remove materials under caissons' cutting edge. We hereby explain the progress of the development of the system both of manufacturing shop and working site with the result through actual operation.
