EXPANSION DRILLING METHOD FOR CAST-IN-PLACE PILE, AND EXPANSION DRILLING APPARATUS FOR CAST-IN-PLACE PILE

PROBLEM TO BE SOLVED: To provide a compact expansion drilling apparatus and an expansion drilling method that curtail operation time of an expanded blade and allow a large-diameter expanded pit to be drilled.SOLUTION: A vertical hole 5 for a vertical pit is drilled beforehand, the vertical hole having a prescribed depth and the same diameter as a casing K press-fit into a ground. A first tier of an expanded hole 14 is drilled by inserting an expansion drilling apparatus 10 into the vertical hole 5 and fixing the expansion drilling apparatus to the casing K, driving and rotating the expansion drilling apparatus 10 by rotating the casing K, to have an expansion blade 12 undergo lateral axial rotation around an attachment shaft 11 and expand outside of an outer diameter of the casing K. Then, a second tier of the expanded hole is drilled by lowering the expansion drilling apparatus 10 to a hole bottom surface 13 of the vertical hole 5, extending an expansion/contraction cylinder 40 to shift outward a position of the attachment shaft 11 at a base of a blade body 35, and having the expansion blade 12 undergo lateral axial rotation around the attachment shaft 11 and expand outside of the outer diameter of the casing K.SELECTED DRAWING: Figure 3 【課題】拡大翼の動作時間を短くし、且つ、小型で大径の拡大孔を掘削できる拡大掘削工法および装置を提供する。【解決手段】地盤に圧入するケーシングＫと同径であって所定深度の縦杭用の縦穴５を予め掘削し、縦穴５に拡大掘削装置１０を挿入してケーシングＫに固定保持し、ケーシングＫの回転により拡大掘削装置１０を駆動回転させながら取付軸１１中心に拡大翼１２を横軸回動させてケーシングＫの外径より外側に拡開させて、一段目拡大穴１４を掘削する。次に、拡大掘削装置１０を縦穴５の穴底面１３まで下降させ、拡縮用シリンダ４０を伸長させて翼体３５の基部の取付軸１１の位置を外側に移動させ、拡大翼１２を取付軸１１中心に横軸回動させてケーシングＫの外径より外側に拡開させて二段目拡大穴を掘削する。【選択図】図３