Abstract: An apparatus for drilling a hole in the ground has a hammer drill installed at a bottom of a rod assembled in multi-stages at support structure on the ground. The hammer drill has a pilot hammer drill and a reamer hammer drill coupled to each other through a key structure formed in the vertical direction so as to allow simultaneous rotations and up-and-down movements relative to each other.

Abstract: The present invention relates to method and apparatus for drilling a large diameter hole in the ground. The present invention comprises a hammer drill (40) installed at the bottom of a rod (104) assembled in multi-stages at support means on the ground comprising a pilot hammer drill (44, 48, 49) and a reamer hammer drill (41, 46, 47) coupled to each other through a key structure (42, 43) formed in the vertical direction so as to allow simultaneous rotation and up-and-down movement relative to each other, wherein in a drilling operation, a repetition is made such that the hammer drill (40) is made to rotate and the pilot hammer drill (44, 48, 49) is lowered to drill a pilot hole of small diameter (w) to a predetermined depth (d) and is lifted up to original position, and then the reamer hammer drill (41, 46, 47) is lowered to enlarge the hole to a large diameter (W) down to the predetermined depth (d).