Pier in difficult to access spot

[bugeater (Marty)]

I really want to set up at least a pier and preferably a small observatory in my backyard so I can be up and running at a moment's notice, plus so I don't have to keen polar aligning. Backyard is large, but very steep and full of trees. So choosing a spot isn't easy, but it will probably be right up the highest point of the block, so it has the best views. But no matter where, access will be difficult.

The thought of hand digging a hole of a cubic meter in my soil (solid clay), plus hand mixing and pouring a cubic meter of concrete fills me with dread. What I wanted to know is whether it is even remotely possible, since I gather you really need to pour the whole lot in one go right?

Alternatively, it seems like a lot of wheelbarrows worth of concrete hauled some distance over tricky terrain. Something like two tonnes of concrete...

It's looking like something like one of those sure foot footings might be the way to go, but I just need someone with the tools to install one...

[glend (Glen)]

I hand dug my pier footing on a sloping block, and hand mixed the concrete for a wet on wet pour - and I'm 65 so it can be done. Saying that it took me two days to dig the pier footing hole in mixed conglomerate sand, rock, clay to get down to the pure clay below. My footing finished up smaller than your one cubic metre @ 750 x 750 and 750mm deep as I was never going to put anything heavier than my NEQ6 head and 10" imaging newt on top. To ensure lock deeper in the ground I also drove galvanised steel angle into the clay at angles to anchor the footing. Shape the footing wider at the bottom if you can. Re bar wired in as well. I bought bags of concrete from Bunnings and mixed two bags at a time in a big bucket and poured it in the hole. I used over fifty bags to build concrete right to ground level and fill the pier form. I was making a concrete pier so the form went on top of the footing pour, after allowing to set enoigh to support it. Reo down the form and into the footing , make sure its vertical and brace if necessary. Pour to top and set the hold down bolts in the top concrete. Bunnings sells concrete anchor bolts (M12) with long L shafts. Keep it damp; while it cures, allow at least three days to cure.

Mix the concrete next to the footing hole so you don't need to haul wet concrete up the hill. I used a hand truck to move the bags of concrete up to the site a few at a time.
You want all the concrete mixed to the same consistency, not to wet, just wet enough to pour. I mixed mine with a long section of rebar to get all the dry clumps mixed. It's hard work no hiding that but it can be done.

Equally hard was hand diggng all the obs post footings. It can be done, just take your time and get help if you need it.

[ZeroID (Brent)]

Beer and BBQ and a few mates can speed it up considerably ...

[bugeater (Marty)]

Glen you've given me an idea.

This site that sells piers
https://www.altairastro.com/altair-s...r.html?cat=303 recommends only about 0.37x0.37x0.9m hole as a minimum.

I was thinking of a roughly 0.3x0.3 hole 1 meter deep, then driving say three 1.8 meter star pickets at different angles into the earth (so embedded at least another 0.8m into the earth). Rebar it all and then pour in the much reduced required amount of cement.

In a way this is a hybrid of the "sure foot"/ ground anchor approach and the big cement plug approach. Plus the initial hole is small enough that you could probably hire an auger to do it.

Main question is would it be as stable (engineers?) and how hard it is to drive a star picket into our heavy clay soil. I'm actually more worried about the second point since when I pulled up some weed matting to plant a new plant I needed to buy a pick just to dig the hole

[glend (Glen)]

I can't comment on your clay but when mine was dry it was like concrete and I had to use a hammer drill to get through it initially. However once down to the wet clay underneath it was much easier to make progress. I was able to drive my angle iron pretty deep. I left enough exposed in the hole to ensure good lock into the footing concrete.

[el_draco (Rom)]

It is possible to build a pier mass like that; just need to be prepared to sweat. Doing it myself at the moment. You may also be able to try some novel approaches though. Look up "Surefoot" and "Mega Anchor" online. Anchoring systems that can hold up a house... EASILY. You can even put the dome on this gear as well.

Other thoughts:
1/ Get a powered auger that will deal with the clay. Very efficient diggers, especially the two man version.
2 Find out if you really need a cubic meter. How big is the scope?