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depth of hole for pier


skippyinspace
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Was planning today to break ground for Bronte Observatory, Well the hole to put the altair astro pier on. Then I realised that I have no idea how deep to dig the hole.

I've read everything from below the frostline (what ever that is!) to 6ft deep.

Any suggestions?

Thanks

Ian

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I have the same pier, I would say anything from 16"x16"x30" upwards.

2' x 2' x 3' will be fine, be aware that getting the last arms reach out without the right tools is pain as i found out LOL (this was my initial plan but a hidden concrete path forced me to change my plan)

But at the same time a 6'x6'x6' would be over kill unless you are planning on a AAA emplacement.

Edited by Earl
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A couple of feet deep is enough in the UK - around 2' cube should do. It is often suggested that you "undercut" the hole so the cast concrete block is slightly wider at the bottom. You can bash a few bits of rebar or scaffold pole into the base of the hole if you like but I don't think this is really necessary.

All this "6' deep" and "below the frostline" seems to come from the USA and Canada where they go in for the use of diggers/cement mixers (lorry kind!) to mount their scopes, usually on the far side of a plot the size of a UK county!!

The frostline bit is for those who live in areas of extreme winter cold, where the ground freezes to considerable depth for some weeks or months every year.

Edited by Bizibilder
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Well done. I'm sure that will be absolutely perfect.

I find all this "bigger the better" stuff quite amusing. In principle there's nothing wrong with that statement, but I think it in-part depends on what use the scope is to be put. For imaging it's obviously critical that the scope doesn't suffer any vibration during the exposures, but I've seen some folks build foundations the size of a military enforcement, when all they intend to do is visual observing. Easy to get caught up in the hype I suppose. :)

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All this "6' deep" and "below the frostline" seems to come from the USA and Canada where they go in for the use of diggers/cement mixers (lorry kind!) to mount their scopes, usually on the far side of a plot the size of a UK county!!

Very true, and made me smile! :)

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My hole is currently about 30"x27" x 20" deep. I'm down to very solid red Devon clay which I think is what might be considered the "bedrock", not actually rock but the alluvial deposit from the last ice-age. Below man-made changes. I'm thinking this will do.

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My hole is currently about 30"x27" x 20" deep. I'm down to very solid red Devon clay which I think is what might be considered the "bedrock", not actually rock but the alluvial deposit from the last ice-age. Below man-made changes. I'm thinking this will do.

It should be fine, if you want to be even more sure, add some steel reinforcements another 12-18 inches in.

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