13.12.2020 Day one of the 4.4m budget dome project: Gravel & concrete!

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After the endless monologues I have actually made a physical start. One car trailer load of self-compacting gravel has been distributed around the edges of the existing observatory "pad." To enlarge it by about a meter [3'3"] all around the precipice. 

I used a builder's shovel and wheelbarrow to ferry the heavy material the few yards from the car trailer to the "building site." Then stamped it into place with my boots to firm up the edges. It doesn't seem to move much, at all, after this treatment.

Self-compacting gravel is a mixture of sand, gravel, small stones and a little clay to bind it solidly. It is easily identified, at a gravel stockist, because it has an almost vertical critical angle. The critical angle is the maximum slope a granular material can tolerate. Before it flows or rolls naturally downhill. Stamp on a steep pile with a work boot and the footprint remains. On sand or ordinary gravel it will usually flow away from the impact site. Particularly when the material is dry.

Self-compacting gravel is best kept slightly damp for maximum hardness and continuing resistance to long term loads. [Like small building foundations.] This is easily achieved if it is laid on normally damp soil. The disadvantage with the stuff I buy is the ginger sand content. Which is carried across the lawn wherever I walk. A thin layer of pea gravel soon solves this problem where the gravel is expected to lie permanently on the surface. The gingeriness soon gets washed off the lawn by the rain. The Danes call it stabil grus. Or self-stabilizing [i.e. stable] gravel. 

Another trailer load should complete the space required for the building extension/expansion. Though I haven't expanded the area enough for a level path around the new building. This would require a whole lorry load! Plus a lot of hard physical effort. Given the drop off, from the edge of the existing pad I will defer a decision on further expansion of the level area.

The image [Right] from April 2017, shows the carport anchor blocks laid out on the original, imported gravel, octagonal, building pad. The proximity of the shed dictated the buildings position and the sheer quantity of gravel required. The covered space was sunken by over two feet [60cm] over much of its area.

I just ordered 12 concrete foundation blocks and brackets cheaply online with very low cost delivery charges. These are the same blocks as I used on the octagonal building and the pier [above]. They have shown no sign of moving or settling. Dimensions are 50x200x200 and their weight is 35kg each.

Thanks goodness I don't follow convention and cast a huge concrete pad the size of the building. Which would probably lie there forever. Any wind which can blow over a building with 500kg of reverse tapered concrete blocks, buried in well settled, self-compacting gravel, will damage far more than just my observatory. A cylindrical building with a dome on top has very little drag compared with a square one with a pitched roof.

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