Dig it by hand.

trench in soil and  person looking at the ground
Digging your trenches for your cob structure by hand allows you to get to know the soil beneath you.
You sees all the creatures and their little homes. The content of the soil can differ greatly from spot to spot. It’s a good meditative kind of work; rhythmic, and slow. When there is a trench to be dung – you have plenty to do! There is a great sense of accomplishment when finished. You gain valuable building material ( clay and or sand ) and a sense of what you structure sits on.
dig. dig. dig.