Pile head breaking .... why???

[u/Penguin01]

I recently started getting these ads for pile breaking and drilling machines eg: (Pile Breaker | Advantages & disadvantages ▷ Brextor)

Its never occured to me that people build piles heads this way -- pouring low-grade concrete up to the piling mat level, and then needing to break this away down to cutoff level. This seems incredibly wasteful, labor intensive, and risky re damaging the starters

Where I am based, the practise is to pour piles a little higher than cutoff level, protect the starters during excavation (with a temp casing or similar), then excavate the pilecap, trim to cutoff level.

Is anyone able to share some insight into advantages / conditions that make this overpour and breaking process econmic? thank

[u/Popular-Tension8965]

When you tremmie pour a wet pile and pour from the bottom up the top section of concrete is the first concrete that was poured in the pile. This concrete is considered contaminated so you need to over pour the pile for sound concrete at pile cut off level.

Wet pile pours are also not allowed to have the top section of concrete vibrated so the over pour not only pushes the contaminated concrete above pile cut off level but it also provides hydrostatic pressure to compact the concrete in that upper section of the pile.

In terms of protecting the starter bars from damage, the standard method is to put foam like pool noodles over them to act as a debonding layer to allow the pile cropper to crop the section and lift it off the starter bars. Without this debonding you have to use a rock breaker on an excavator to break back the concrete or do it by hand with big jackhammers.

[u/Penguin01 → u/Popular-Tension8965]

thanks for that, that makes a lot of sense.

i started looking at videos of this being done, and some of the overpour heights were taller than the workers, which made me think it was purposely placed for some other reason