why shingles are used in piles

huangyhg

why shingles are used in piles?
crushed stones are used as aggregate for concreting main structural members. but why shingles are used as aggregate for concreting piles?
where have you seen shingles used as concrete aggregate?!  please explain.
and what do you mean by the word "shingles"?  it can mean several different things.
like a skin disease.
shingles : this is larger sized water worn stone found near sea shore.
shingles are very much round and with smooth surface. but these are used as aggregate in piles. why these are used in piles?  
i suppose it must be a locality based thing.  it is possible that smooth gravel and cobbles (what i would call your "shingles") would be acceptable aggregate in bored piles.  this type aggregate does not produce high quality concrete, and would not be my choice.  if used, the gravel should be washed, free of all salt.
i think that i would like to know what type of pile you are using.  some are thinking, as hokie66 that it is a bored pile where the load transfer is throughout the concrete - and this is likely the case.  i have used concrete to "fill-up" closed-end steel tube pipe piles and the pile strength did not take into account the capacity of the concrete - it was based on the steel shell - in this case it doesn't matter what type of aggregate you would use as the "filling" material.  this is why it is so important for all of us to fully describe our problem in ors.
i'm guessing that rounded aggregate concrete will flow better which could be an advantage for piles.