One of my design goals was to make sure that down the track I could move the dome if required. This combined with much advice that a floating deck is a better approach than a concrete slab for a couple of reasons:
- Much lower thermal mass with air flow under the dome.
- The challenge of getting a round concrete slab really level.
- Domes on concrete slabs often seem to have damp/water issues.
- The easy running of cables for power, network and more.
I found a local digger contractor with a large 600mm auger bit and we used that for the pier footing. The hole is over 2000mm deep with about 1 cubic meter of concrete in it. The deck footings are 300mm diameter and ~600mm deep, some deeper based on the soil. The pier footing has a big piece of reo mesh bent into a circle to add a bit of strength, and then the bolt cage is sitting above that.
All up about 1.2 cubic meters of concrete delivered in a mini mixer. Concreting is hugely physical, and being able to pour the main pier footing directly is a huge saving of effort. All the footings are agitated to remove air bubbles. The bolt cage was carefully aligned to south using a bit of formply to box up and hold the cage in the correct position. I won't lie, the concrete pour is a fast and furious process so I was very nervous until I had the pier in place and could confirm that it was both very nearly perfectly level, and also aligned to within a degree of south.
If I had to remove the dome the 6 deck footings would break up fairly easily. The main pier footing is level with the ground level and the top could be broken up to a degree with some effort, but the main plug isn't going anywhere fast. I can report now over a year later than there has been no movement of the pier.
If I did it again I wouldn't change a thing.