Why are we looking into trenches? Unless our friend is planning on building a house there,,I thought it was for a shed? He wants nicely compacted gound, so why disturb it any more than really nessesary, slice off any high spots, but try not to break up the ground. My 12ft x 12ft block built shed is built on a 3 or 4 inch slab sitting on fairly undisturbed ground, i threw in some sheep netting and anything else that could be used as reinforcement esp around the edges and despite tree roots, a mature plum tree right beside it, and parking 3 motorbikes plus plenty of other junk on it Ive had no issues at all over 25yrs,,no cracks, nothing. Rotovating seems to be the last thing you want to do in a situation like this?
Steve.