driven piles...energy per blow and se

huangyhg

driven piles...energy per blow and set
hi guys,
i haven't dealt too much with the design of precast driven piles but today i was given the job of specifying the hammer mass, drop height and set of a driven pile.
i spoke to a piling contractor over the phone to try and determine a generic hammer mass and drop height, only to be told it depends on a number of factors and the contractor needs to know more specifics of the job before they can give an answer.
basically, the mass of my pile is 12 tonne (26,400lbs) and i was thinking of using a 12 tonne drop hammer. if i drop it from a height of 900mm (3ft) and using a efficency factor of 0.95, this gives me a energy per blow (10.3 tonne meters). my question is:
how do i know what energy input per blow is required to drive the pile? i am driving through silty clayed sand down to weathered sandstone (rock).
i am also required to specify a pile set which is given by a hiley formula:
s=9800x(mm+e^2*(mf+mp))/(mm+mf+mp)*e/r-0.5*c
where

mm=hammer mass
mf=mass of pile helmet
mp=mass of pile
e=co-efficient of restitution, 0.25 to 0.4
e=energy input per blow (calculated above)
r=minimum ultimate capacity of pile (3200kn)
c=combined temporary compression of the helmet cushions, pile and adjacent ground in millimeters.

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i'd advise that you consult a local or the project geotech
asixth - msucog is right. also, on many projects selection of the hammer is left to the contractor (with approval by the engineer). this helps to increase bidding completion since various contractors have (cost-effective) access to different equipment
however, if you have to do this project yourself, a good place to start is with the us army corps of engineers publication, "pile driving equipment". a free download at this link: