Some piling contractors incline to use drop hammer instead of hydraulic hammers in setting of piles. Why?

The use of high grade and heavy steel pipes may not warrant the use of drop hammer. For pile driving of Grade 55C steel section, it requires heavier drop hammer with increased drop height so as to comply with penetration resistance at final set. As such, it is possible that such heavy hammer may damage the pile and endangers the worker who takes the final set record.

Though hydraulic hammer is commonly used as standard hammer for driving piles, some piling contractors prefer to employ drop hammers to take final sets. The obvious reason of such practice is that it is convenient for drop hammer to change energy input easily to cater for the range of penetration in final set. On the other hand, the use of hydraulic hammers for setting of piles requires the knowledge of transfer of energy to pile head and hence needs the input from wave equation analysis.

This question is taken from book named – A Closer Look at Prevailing Civil Engineering Practice – What, Why and How by Vincent T. H. CHU.