in my region we are mostly black and red clay which shifts with the wet seasons considerably and patio paver patios just will not stay level and will not stay as you would expect.
even when digging down 8 inches and installing compacted rock and then heavy sand for the base. We just have up heavals and down falls all the time thus an unsafe patio.
I also would not go the RR ties or PT ties as they will leach out stuff and will also buckle at times.
The Cinder or haydoc block idea might be the best and would definately last the longest.
Personally, I would make the patio paver deck area, then build a pt deck that covers the low spot. This would look nice in my opinion.
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