Best way to dig holes for posts?

[Tubby2]

Gday all,
I'm just about to start on my timber sleeper retaining wall and need to dig about 30 holes for the posts to go into.
Only problem is that half of the holes will be into shale!
I can get hold of one of those hand held post hole diggers to dig the holes in the clay but what should I be using to dig into the shale? A big crow bar? bobcat with auger or rock breaker? I'll be using 200x100 sleepers going in about 600mm.

Cheers

[Cliff Rogers]

Arh, this is an old joke, you buy an old mineshaft & cut it up into lenghts you want.

[manoftalent]

get a bobcat mate, it'll save ya a heap of pain later ...

[Brickie]

Ive got some spare post holes left over from a job if you are interested?

[Planned LScape]

You could get a small excavator bloke or bobcat with auger to come and have a look, some softer shale will break apart easy and the auger bit will drill though. Any harder though, the the auger will either skew off line (which wont help your wall), or it will not even go down 200mm.

What I've done in the past is either hired a kango hammer (or a bigger jackhammer) and broke out the rock while the guy on the machine was doing other holes, or otherwise the machine operator may have a hammer attachment than can drill/hammer till the hole gets to depth. The only downside to this method is the hole will be bigger than first anticipated as the machine hammer attachment makes the hole bigger due to the body of the attachment.

[munruben]

Arh, this is an old joke, you buy an old mineshaft & cut it up into lenghts you want.

I got plenty of socks with holes in them but I don't think they would be big enough.

[munruben]

Wouldn't a Jack hammer do the job.?

[Tubby2]

Thanks guys,
A mate of mine has a small excavator, one of those 900mm wide ones. He actually dug out the back yard (took out 60tonnes). He does have an auger but seems to think he wont be able to dig thru the shale with it. He suggested having to dig a trench which I cant see being as structurally sound than just a hole.

[Planned LScape]

Just hire either a kango or a compressed air jackhammer...get him to start the holes and go as deep as he can go before it's into rock (while putting some water in the hole to make digging and removing spoil easier), and when he cant go further you loosen it up with the hammer...it wont take long at all