Permanent Pier Concrete Base

[Saturn488]

There is a lot of information out there regarding how large and deep a base should be for a pier but it isn't consistent. Some people dig holes as large as a small country to barely enough to fit a toothpick.

Eventually I will be building an obs but for now I would like to install a concrete base to put my steel pier on (which I dynabolt down so I can easily remove it at anytime).

At my old house I had it still on a pad around 600x350mm and around 500mm deep. For 3 years it held polar alignment and worked perfectly.

What I would like to do is install two of these concrete bases and eventually build my obs around it which will be a raised timber floor.

How wide and deep have you dug your holes for your piers?

[Leo.G]

There's a few suggestions in the following thread by people who have done their own piers:

https://www.iceinspace.com.au/forum/showthread.php?t=213080

My hole is 600mm square and 700mm deep so I could put some gravel and cement powder in to prevent the clay sucking the moisture from my concrete mix and cracking/weakening it when I get to it. The 3/4" rebar is driven in around 1 metre at between 40 and 60 degrees radiating out from the hole at each corner, it should never move. I'm not an engineer (not that kind) so it may not be as solid as I'm hoping but maximum weight will be pier (heavy) pus EQ5 Pro head and a 152mm x 1200 Skywatcher Achromat refractor plus maybe Nikon full frame camera or my 8" GSO f5 Newt and Nikon. The pier is the heaviest part. I think if it moves once installed we've had an earthquake.

I have everything almost ready to go (for too long now) and have had something just come up which is going to keep me occupied for the next few weeks so hopefully late February it will be complete. Then it probably wont stop raining (half of my problem already).
I used to often see mention of 1 cubic metre of concrete, 1x1x1. When I looked into it, that's a LOT of concrete, more than I'm mixing in my wheelbarrow. In saying that my pier is solid and heavy but my equipment isn't, so the pier is over klll but I got it cheap locally and it saved me having to weld my own despite having pipe, plate (up to 1.25") and steel bar ready to go. If I ever get a better mount and heavier gear (finances permitting) the pier will eventually handle it.

[Saturn488]

Excellent, thanks for the reply and link to the thread!

[Leo.G]

Sorry, I forgot, there's a second thread in a different section where I'd asked some questions which may also have information relating to a pier slab:


https://www.iceinspace.com.au/forum/showthread.php?t=209321

[bojan]

Here is my solution to the problem ...
https://www.iceinspace.com.au/forum/showthread.php?t=176799&highlight=observatory&page=2

[muletopia]

Hello,
This link
https://www.iceinspace.com.au/forum/showthread.php?t=135400
details my base build for an observatory pier.
It served me well for ten years,it needed polar alignment twice per year as the soil dried out and became saturated. It,and the observatory have been dismantled and transported to my new home on the Darling Downs in QLD. This time I will not build a cage in the concrete but use concrete bolts (not rawl plugs) to attach the pier to the concrete as they are secure and the pier base will be easily shimmed to correct the inevitable error in leveling the concrete. This obs will have mains power so all the fiddle of a solar panel supply is avoided.
The HEQ5 mount originally mounted was inadequate so it was replaced with a Mesu Mount 200 MK1.
Might interest you
Chris

[Saturn488]

Appreciate the links and all the useful information!