After three load in my carpet lined boot of the Kia Sportage, has resulted in 200 bricks, all made by local brickworks now defunct. I ran out of steam, but I’ll get some more next week.
The topsoil here is about a spade deep, and then it’s shiny clay. Korean Natural farming have suggested that pouring potato water to feed and promote indigenous microbes will help break down the clay but I’ll need to find more research. The method is simple, fill a 44 gallon drum (55 gal in the US and 210 l in Eu) with water, heating it and adding some potatoes and boil. When soft use a paint stirrer and mush the lot up. Strain and spray onto the soil.