Underwater pile driving tool

A tool for use in submerged condition for installing piles in a ground formation that is submerged under a body of water, comprising:

• a hammer body that is adapted to be fixedly supported relative to and in axial alignment with the head of a pile that is to be driven;
• a reaction body carried by said hammer body and guided for movement thereon in a direction that is axial to the pile that is to be driven;
• said hammer body and said reaction body respectively defining opposed first and second ends of an expansion chamber that is formed therebetween;
• charging means for creating a rapidly expanding volume of high pressure gas within said expansion chamber to generate a downwards pressure force pulse on said expansion chamber first end to drive the pile, an equal and opposite upwards pressure force pulse being applied to said reaction body through said second end of the expansion chamber;
• and
• damping structure operatively associated with said reaction body and configured to interact with the water in which the tool is submerged to resist upwards movement of said reaction body in response to such upwards pressure force pulse.