Patent ID: 7651301

Claim:
A drilling head attached to a lower end of a rotary shaft to be penetrated into the ground, comprising: a plurality of spiral blades arranged at regular intervals around an axis of rotation of the rotary shaft; and drill bits attached to a lower edge of each of the spiral blades, wherein the lower edges of the spiral blades define an envelope with a central part thereof rising in an upward direction from an outer circumferential part thereof as the rotary shaft is rotated, wherein at least one of the spiral blades is provided with an ejector arranged on a back face of the spiral blade and is configured to eject a resistance reducing fluid that is supplied from a source installed on the ground toward the ground to drill, and wherein the ejector comprises: a first ejection mouth configured to eject the fluid in a forward direction of a rotational direction of the spiral blades; a second ejection mouth configured to eject the fluid in a reverse direction of the rotational direction of the spiral blades; and a third ejection mouth configured to eject the fluid in an outward radial direction of the rotational direction of the spiral blades, wherein one of the first, the second, and the third ejection mouths is selectively opened.