8 grip the wall of the borehole while the application of pressure to the chamber a has the effect that the drill rod 7 exerts an axial thrust on the bottom of the borehole consequently cracks are produced in the wall of the borehole which are perpendicular to the axis of the borehole and hence parallel to the free surface as mentioned above it will be achieved by the above described method and apparatus that the face of the rock can be pulled out in flat flakes along the longitudinal axis of the apparatus the drilling action by rotating the bore drill 7 about the longitudinal axis of the cylinder housing 11 can be performed simultaneously with the above described gripping action or both actions can follow independently of each other the latter will be carried out in such a way that the drill rod 7 will be shifted axially in said cylinder housing 11 independently in advance of the piston 2 for a distance which is at least equal to the actual length of the gripping means 8 the wedge sleeve 9 and the gripping means 8 may be introduced into the borehole during or after the drilling once the central drill rod 7 the wedge sleeve 9 and the split gripping means 8 are in the borehole the apparatus may be made besides drilling actions to exert radial as well as axial forces on the rock by introducing the pressure fluid into the chamber b which lies intermediate the pistons 6 and 2 the pistons will be pushed away from each other whereby the stop 3 of piston 2 comes out of engagement with the collar 4 the drill rod 7 ceasing the axial thrust on the bottom of the borehole and the piston.