Building the extension to the outer core of the biomeiler followed a procedure nearly identical to that which I described in my last post.
I began by clearing away the insulating layer of wood shavings. Next, I attached the perimeter fence. Lastly, I filled the extension with alternating layers of used chicken litter and thatch raked from the yard. Thermocouples were added halfway between the inner and outer radius at elevations of 4 feet and 5 feet above the ground.
The outer core extension has the geometrical form of a ring with an inner radius of 18”, an outer radius of 36”, and a height of 28”. As such, it has a volume of 48.8 cubic feet.
As I finished filling the outer core extension I observed that, despite my efforts to the contrary, the perimeter fence was clearly off-plumb. Imperfection is much be expected in a pile of such materials, but I had been taking pains to keep the walls close to vertical as I filled the volume.
Overnight, the situation worsened. My hypothesis is this: the additional weight of the inner core and outer core extensions is unevenly compressing the material in the original cores. There is no significant danger of collapse, but I will try not to delay unduly in constructing the mantle extension, which should provide additional stability. Any future construction will have to be undertaken with this observation in mind.
Fence lengths are not the ideal material for use in the pile because the compost material pulls downward on the horizontal wires as the pile subsides. When I built the biomeiler, I needed a way to fasten the PEX pipe in place to form two vertical spirals extending through the pile. The fence material was convenient, but there is a risk that the PEX pipe may be kinked at the fastening points if the pile material pulls it downward too far.
Consideration of the problem brought a solution to mind. In the future, I could employ vertical pipes as the perimeters of the cores and let the PEX pipe slide down around it when the pile subsides. These vertical pipes could potentially be used for aeration, gas content monitoring, or for adding water to the cores after the pile is in operation.
In the world of biomeiler research, I find there is great scope for the imagination.
You don’t lack in imagination, Sir!