A drill head has a domed leading face and carries cutting teeth. A tubular drill string can be used to drive the head into the ground. An off-center aperture communicates with the bore of the string, by means of a connecting passage, which defines an oblique cone. During drilling, a flushing medium can be pumped down the bore and out through the aperture. As the drill string and head are withdrawn, an elongate member can be introduced down the bore, out through the aperture, to be left in the passage drilled by the head. The form of the mouths and connecting passage avoid the elongate member encountering any discontinuities which would prevent it leaving the head. The elongate member could be reinforcing bar for a cast-in-situ pile, or part of a ground loop for a ground heat energy system.