Load testing of piles

[Hariharan]

I presume load testing of piles under bridges would be still common
around the world. I would like to know the practice of deriving
safe working load of the piles from load tests for large
diameter piles. i.e., what is the load/settlement upto which
the pile is tested, and what is the method of deriving
safe working load? For example, one criterion is
"Safe working load is 50% of the load corresponding to
a settlement of 10% of pile diameter". If any other practice is
followed, could we have it elaborated here?

Thanks,

Hariharan