I have a cherry tree with a three inch (≈ 80 mm) trunk, and I want to
landscape the ground upward around the trunk a couple of feet (≈ 60 cm).


Forget it. If you raise the ground level that much you may suffocate the tree
long before you get any girdling roots. If you were going to raise the
surrounding ground level by a foot or less, you could build a retaining wall
around the perimeter of the root system. For the change you anticipate, the
only practical solution which will save the tree is to lift it, with the
rootball more or less intact, and replant it at the new level or plant it
somewhere else. If the tree is valuable, you may need a professional arborist.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"A tree never hits an automobile except in self defense." - Woody Allen