Rotary drilling device

A rotary drilling device of the type having a body connected to a rotary drive system for rotation about a primary axis in order to bore into the ground to form a cylindrical hole having a bottom and side wall, said device comprising:

• a rotary cutting member mounted on one side near the bottom of said body for rotation about an inclined axis of rotation which forms an angle with the primary axis of rotation, the cutting member being inclined towards the bottom and the side wall of the hole, the cutting member being shaped to form a hole with a substantially concave bottom;
• and
• a counter-reaction member disposed on the side of the body away from that carrying said cutting member and near the bottom thereof, the counter-reaction member being constructed and positioned so as to be in contact with only the concave bottom of the hole and so that the maximum radial projection from the primary axis of rotation of any part of said counter-reaction member and its means of attachment to said body is less than the radius of the hole, with the highest point of the surface of contact between said counter-reaction member and the hole being situtated below a line defined by the intersection between the concave bottom of the hole and its cylindrical side wall, said counter-reaction member having a convex surface in contact with and closely conforming to the concave surface of the bottom of the hole.