Why are vibrators not used in concrete compaction in piling works?

Concrete for piles should be a high-slump self-compacting mix which is capable of flowingbetween reinforcement cage with ease. Since concrete is designed to be self-compacting,vibrators are not used for providing further compaction. Moreover, the concrete in piles iscompacted by energy derived from free falling.

However, if vibrators are used, the vibrated concrete may be compacted to the sides of the concrete casings and hinders the lifting up of casings.

1- to avoid soil collapse during pouring

2- it is very deep to use vibrators

3- the most concrete for piles is fluid

4- there is special system for compact concrete for piles by the vibrate the concreting pipe it self during pouring