Laying concrete slab driveway

[hyposmurf]

Looking at replacing ome driveway concrete slabs.They are approx 600mmX600mm.The existing cracked slabs were laid with sand underneath and a nearby trees roots I guess with movement overtime and the car loads going over them have cracked.Maybe also were the soil dries and then absrbing mositure creating movement underneath.
How is best to lay them?Should I be using sharp sand?Concrete as well?Waht type of depths?If I use a oncrete base surely this will hav less give in it whn loads go over it and then more cracks?Also the driveway is on a steep slope, so it would be impossible to use a level to get a good finish.Any ideas?
Do I need to set the slabs slightly proud of the existing slabs as they will bed down with the car loads?

Thinking of setting out a taught string to get a straight edge as existing slabs have moved in different directions.I would then look at laying 60mm of sharp grit sand and compacting it as much as possible,trying to acheive a smooth finish.Then add new concrete slabs.

 

[dextrous]

To do a proper job, you need to incorporate about 8" of compacted hardcore beneath the driveway and about 2" of dry sharp sand/cement mix (about 3-4 sand to 1 cement), again compacted and levelled (as is smooth with no troughs, and not with reference to the slope)