Someone brought up pile driving. I did inspection on a local bridge I watched them drive the piles. The pile driver is basically just a two stroke diesel. The crane lifts the driver with a rope and as it comes down it shoots diesel in which fires and drives it back up. You are suppose to count the blows per inch, there is a chart that you look on before hand, but you can almost tell by the sound when it’s done.
The engineer estimates (guesses) before hand how long the piles will be. They don’t want then too long, they just get cut off and wasted, but if they are too short they have to weld more on and they get paid big bucks for that.
Around here I don’t think the piles ever come back up, they can build on them right but it takes a few days to get the forms up and rebar installed.