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Old 04-01-2015, 07:43 AM
glend (Glen)
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glend is offline
 
Join Date: Jun 2013
Location: Lake Macquarie
Posts: 7,121
Pier Footing Question

I am digging my pier footing for my ROR observatory, and need some advice on sizing. First I have read through what seems like a hundred different threads on various forums regarding pier design etc. This pier will be a full concrete one from footing to the adaptor plate. What I am struggling with is knowing when I can stop this horrible digging. My footing hole at the moment is 500 x500 x 600 deep in what has to be the hardest ground I have ever had to deal with. The soil is a mix of compacted sand and clay and small stone aggregate which seems to be in a ratio appropriate for concrete itself. The only way I can progress with the hole is to use a big breaker bar and my hammer drill with a masonary auger bit to drill holes in the bottom that I can then break up with a small mattock. It is back breaking work for an old man.
I know the footing size is all about the type of ground so I'd like some opinions on just how far I need to go? I intend to widen the hole out at the bottom before I put the concrete (and reo) in. The mount is a NEQ6, and the largest scope used will be my ultralight 10" imaging newt which weighs about 14KG with everything on it. My current tripod sits at 805mm high to the base of the NEQ6 head, so I am thinking that the pier column will be no longer than that inside the ROR Obs (which will sit on treated pine footings). The pier will comeup through the floor and not be attached in anyway to the building, so I am thinking a max length of the pier to be
something like 1200mm allowing for distance to the top of the footing below the building. The concrete for the pier will be poured into a tube form and there will be reo in the tube.

So how far to towards the centre of the earth do I really need to go?

Last edited by glend; 04-01-2015 at 08:11 AM.
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