Undervanns-paeledrivverktoy

A tool is provided for use in submerged condition for installing anchor or foundation elements such as piles in a ground formation that is submerged under a body of water. A hammer body is fixedly supported in axial alignment with the head of a pile that is to be driven and carries a reaction body guided for movement thereon in a direction that is axial to the pile. The hammer body and reaction body define opposed first and second ends of an expansion chamber. A pyrotechnic charge is initiated to create a rapidly expanding volume of high pressure gas in the expansion chamber to generate a downwards pressure force pulse to drive the pile, an equal and opposite upwards pressure force pulse being applied to the reaction body. Damping structure operatively associated with the reaction body interacts with the water in which the tool is submerged using the inertia of the water to resist upwards movement of reaction body.