Another patio one!

The area in question is the same for many many years, no trees removed, hedge planted maybe 20 odd years ago. It's a very large site and stepped up to back garden which is quite long and this is at the very back/top of it, field on other side of hedge.

Lot of topsoil removed but not sure how deep it goes as the soil there is lovely stuff for planting in, everything grows very well, former field itself!

I couldn't see how the topsoil if some is left under it washed away anywhere, no where to go, it's nice and dry up there in general, water just soaks in nicely and doesn't pool around the place.

Either way they are buckling and uneven and if the only solution is a concrete base then I assume it will need to be thick enough not to crack if anymore movement. Access isn't great either as when the job was done there was a sort of ramp built to allow small digger up there but then existing wall was raised and new steps put in so lugging up stuff/mixer to mix concrete won't be easy! Plus I don't want them to destroy the lovely path/steps/plants etc on the way up 🤔

So all in agreement that concrete is way to go! Now that I don't trust anyone who seems to know what they are doing what sort of depth of concrete should we be looking at? Anything else I should be asking the guy about the job, want to be as sure as possible it doesn't split and crack and end up in same boat further down the road.

Actually oddly enough I have two old patios and a large porch with slabs also, I notice the oldest patio which is here since 1991 has become more uneven over time and while still flattish unlike this new one there are definite variations in the edges of slabs that were not like that always.

My porch which is surrounded by pillars/path so totally enclosed and roofed but is open is very level but yet there is one slab that has also come up slightly on one side, cannot think of any explanation for that, I have only noticed it this past year or so, wondering is there an ants nest or something down there!

Third patio is very small, one of those interlocking circle type and was put down maybe 20 yrs ago, hilariously by myself and it's the flattest of the lot! Nothing has moved and all slabs remain level, I repointed them last year with some good stuff as the filling was never a great job but it's pretty perfect if I say so myself. It was on sand only as I knew no better, other one is I presume sand as well, it's definitely not concrete and the porch slabs are on sand definitely at one side as there unfortunately is a manhole under there that sometimes has to be accesssed, the rest might be on concrete, they have not budged other than one that has defintely risen up slightly recently.

Talking about roads motorways in fairness probably have a serious layer of stone not to mind the top coat. Local ring road around here built few years back is constantly sinking in places, two repairs alone in this past year and there is another obvious dip there again in a different position. Every road in the country would be lovely and flat if they stayed the way they were day one but there is a fair old few dips and bumps when you drive around them!