An Evaluation Of Hydraulic Vs.Steam Pile Driving Hammers

Abstract Hydraulic hammers have received much publicity in recent years, and much emphasis has been placed on their advantages. This paper makes a detailed evaluation of hydraulic and steam hammers' advantages as well as disadvantages, showing experience data from offshore installations and interpretations by computer analysis. Aspects considered are: energy output; driving efficiency; influence of pile geometry on relative performance; efficiency of gas buffers, asbestos cushions, and wooden cushion blocks; hammer weight and the maximum free pile length that is allowable as a consequence; driving rate; reliability. Different underwater applications of "thick" and "slender" underwater hammers are dealt with. 1. Introduction Since the introduction of large hydraulic hammers for offshore platform installation (1975), they have been given much publicity. Justifiably so, because the hydraulic hammer is a fine innovation. It is the great achievement largely of the late Joost w. Jansz of Hollandsche Beton Maatschappij, designer of the HBM Hydroblok. The steam hammer, which has generally been in use for offshore pile driving for a long time, has been under frequent attack in the Hydroblok publications. Hydroblok advantages were heavily set off -against steam hammers; usually basically correct, but sometimes lacking relevance. Meanwhile, steam hammer manufacturers did not correct the publicity balance, maybe being sufficiently confident about their market position or themselves lacking the necessary offshore experience. The author's company has gained experience in working with both hydraulic and steam hammers, and throughout the years has had to make proper investment decisions which necessitated comparing hydraulic and steam hammers objectively. This paper intends to make plain fact comparisons between hydraulic and steam hammers. These comparisons can be made on the basis of the author's own experience with both hydraulic and steam hammers; case histories made available to the author's company; and comparative theoretical analyses. 2. Description of hammer types: basic differences Large steam hammers (fig. 1) are mostly made by Menck and more recently also by Vulcan. They are single-acting, Le. the ram drops by gravity and is forced upwards by the supplied steam. It drops on a cushion contained in the anvil which rests on the pile. This cushion is of bongossi hardwood for Menck steam hammers, and of asbestos/steel laminations for Vulcan hammers (figs. 4 and 5). Most Hydraulic underwater hammers have been made by HEM (fig. 2); Menck has built one thick model comparable to HEM's Hydrobloks, and also one slender hammer (fig. 3) Hydraulic hammers are double-acting, i.e. the rams are forced both upward and downward by hydraulic oil. In the case of HBM hammers the drop weight contains a gas buffer with an impact head; the impact head strikes the anvil, so that the drop weight's impact is cushioned by the gas buffer (fig. 6). Menck's thick hydraulic hammer has a similar cushioning through a gas buffer located not in the ram, but in the anvil, where steam hammers have their wood or asbestos cushions (fig. 7). Menck's slender hammers have specially-shaped steel anvils, needing no buffer (fig. 8).