Keep filling... keep putting more layers of pipe in.. I ended up with 4 layers, but the ones directly above each other didn't take the same path.
The pile of earth is slowly getting smaller!
I've put the neighbours fence back up too, the minidigger driver accidentally knocked it down!
I slotted 4 inch polystyrene around the perimeter, and started backfilling all the dirt. Inside I put two blue barrels as manifolds (one 'in' and one 'out'), and put 80mm perforated drainage tube between them- the idea being eventually I will use a fan to blow hot moist air down these tubes. Under the cool soil the moisture will condense and the air lose heat- storing the heat underground and dehumidifying the greenhouse. This is called a 'subterranean heating and cooling system' or 'climate battery', and is used on a much bigger scale at the Rocky Mountain Permaculture Institute in Colorado, amongst other places.
This is the second pipe layer. I've tried to make all the pipes the same length but it is a struggle getting them round the IBC- should have put it a big further forwards!
So we dig a big hole, and sunk an IBC in it for water storage. We reached 90cm deep.
And then built some pillars with hollow blocks- these cost more than bricks or breeze blocks, but I can't bricklay and with the hollow blocks all I have to do is pour concrete into the holes.