Abstract: Apparatus for use in driving a pile by means of successive hammer blows at the same time as a vibratory force is to be applied to the pile comprises means for simultaneously transmitting, to a pile to be driven, a force produced by a hammer blow and a vibrating force which is generated by the application of the hammer blow.

Abstract: An electro viscous vibrator comprises a double-headed dumb-bell shaped piston, of which the two heads are each axially movable within a separate cylindrical chamber, and a pair of concentric annular electroviscous valves in each chamber surrounding the piston head contained therein. Each pair of valves is preferably constituted by an annular electrode assembly disposed between the wall of the respective chamber, and the associated piston head, each valve of the pair being constituted by one of the two annular gaps thus formed between the chamber wall and the electrode assembly and between the electrode assembly and the piston head, suitable electrodes being located on the electrode assembly.