Digging holes to concrete fence posts

I also got through 20-30cm of compacted RC with a hand earth auger of a no-name brand. After that, I only had sand, which was easy then. Watering is a good idea and maybe at the beginning a pickaxe so that the earth auger gets "grip".

Is the earth auger ruined after a few holes in gravel or does it hold up well? I hadn't even thought about an earth auger for my carport foundations yet...

What do you think in this case of an earth auger/pile drill with SDS chuck? From my point of view, it would be significantly easier and faster?

If it were only clay, that would be possible. But it is partially interspersed with large stone chunks. I think I will really make the holes wider then.

How long such an earth auger lasts probably depends on the quality. I have to say my no-name one looked scratched after the RC but still okay. But it was only a few cm. If you really want to go through 80cm of gravel, it can of course look different.

With SDS shank. No idea. I suspect with a wide handle you can apply more force. It's not about applying force on a tiny little point here. You have the lever on the outside area.
Better to get a cheap power drill from Scheppach or something like that and maybe sell it again afterwards.

I had really hoped to finish the holes in one day :-) But as I see it, I will need several days just for the holes. I am trying to find something that makes the work easier for me.....