Exactly as you described - if he just pushed the dirt back in and they and they compact it to drive the Skid over to gain better access I share the same concern around the weight and damage on plumbingYes, I was misinterpreting his proposed approach. I thought he was wanting to put gravel in trench even in the green areas and you were questioning how to fill the trench without access to the side of the trench. Which I would highly recommend instead of the virgin soil. It appears to be all clay and this might make the trench very soft for the remainder of the build a wheeled skid steer with a load could potentially sink down far enough to damage the plumbing.
So to get back to the original question you seemed concerned about backfilling the trench so they can have access to the back yard. I am not clear on what those concerns are.. ¯\_(ツ)_/¯
PB is coming over tomorrow, I’ll spend more time addressing this with him and asking why not just start gravel at pad through the green area to create a stronger base for skid to access and then begin removing all the mounds of dirt
knowing we want to plant grass there - how much topsoil do you thing we will need on top of the gravel for those green areas ?
sorry about not presenting the issue as clearly as I needed too - a lot easier when you are just standing back there and looking at access challenges and mounds of dirt and trenches