We have a long term renovation project in the French alps, vehicular access is via a 30 metre long grass covered "drive way" which slopes gently upwards to a height of about 1 metre over the length of the drive. In anything other than dry weather, car access is entertaining to say the least. The local council has a dump of gravel not far from us, and it seems to me that one night we could easily "acquire" enough gravel to lay two lengths of gravel to aid vehicular access. My question is, should we dig out two parallel and shallow "ditches" to take the gravel (and if so, how deep should they be?), or just lay the gravel straight on to the grass and bed it in by driving a car over it?