is placed in a forward direction the driving effect is achieved by a spring urged forward head 27 slidably mounted on the casing 10 preferably the valve gear in the casing incorporates reversing means whereby the piston can be caused to move towards the rear of the casing at a greater energy than its return towards the leading end of the casing so that the piston 30 impacts against the rear impact anvil 28 to cause reverse movement of the tool this reversing valve gear may be controlled by a control cable 40 or a further hydraulic line leading from the rear of the casing a shackle 42 may also be provided on the rear of the casing to facilitate rearward movement of the tool by a heavy duty cable 50 attached thereto the tool of the present invention is particularly advantageous in a piling operation where it is driven vertically into the ground or at an angle close to the vertical in a location where a pile has to be formed and when the tool has reached the desired depth it is withdrawn from the hole either by reversing the hydraulic supply thereto or by withdrawing it with the aid of a heavy duty cable as the tool is withdrawn comentitious grout can be supplied under pressure through the flexible supply line 22 and the central passage 18 to fill the void left as the tool is withdrawn and thereby form the pile it will be realised of course that the hollow nature of the tool makes it suitable for other operations for example for pulling cables through soil etc a further advantage of the machine is that the resistance.