Abstract: A drilled hole (1) is produced by means of a drilling rod assembly comprig a succession of rod elements (7d) to be arranged end to end. For this purpose, a vertical shaft (2) is produced in the ground, of constant horizontal section and preferably insufficient for a man to be able to work towards the bottom of it, the rod assembly is displaced therein from an opening located in a front wall of the shaft, and the elements (7) of the rod assembly are selected so that they have an axial length less than the distance separating the said opening in the front wall of the shaft from the opposite rear wall.