Apparatus for providing an underground tunnel.

摘要

An apparatus for providing an underground tunnel utilises a steerable, powered, elongate percussive downhole hammer (14) having a cutting bit (16) which is asymmetrically configured with respect to the axis of the hammer (14). The hammer (14) is steered through the ground, that is, made to move along a straight path or a curved path, by controlling the way in which it is powered and/or the way in which it is urged forward and/or the way in which its cutting bit (16) is rotated.