Abstract: A method wherein a hole is made in the ground having the depth intended for a diaphragm, the hole being a narrow cylindrical cavity. Into this cavity is successively inserted a drill head including at least one ejection element having its axis aimed in a direction transverse to the axis of the cavity. The head is connected by means of a one-piece flexible tube to elements which supply the substance to be used for reinforcing and waterproofing the ground under pressure to the ejection element. The reinforcing substance is discharged through the ejection element at the same time that the head is drawn toward the surface, the axis of the ejection element being maintained in its oriented position in a controlled manner in a plane perpendicular to the axis of the cavity to form a diaphragm.