Excavation method of ground in open caisson method

摘要

Provided is an excavation method capable of softening hard ground from a specific depth when the hard ground is reached during construction of a caisson. (1) When the cutting edge of a caisson body 1 reaches a hard ground, a plurality of preceding holes are drilled in the hard ground G2 at the bottom of the hole by the same procedure as the all-turn all casing method. (2) As a small-diameter excavation using the excavation head 7 whose excavation diameter can be changed, excavation is performed so as to expand each preceding hole to form a medium-diameter hole H2. (3) As large-diameter excavation using the excavation head 7 whose excavation diameter can be changed, excavation is performed so as to further expand each medium-diameter hole H2. This large-diameter excavation cuts and breaks down the hard ground G2 and is stirred and crushed, and is replaced with a soft soil layer G3 that is softer than the hard ground G2. [Selection diagram] FIG.