I have just finished renovations that included excavating a fair amount of dirt from our back yard. This has left me with an area about 5m x 10m that I need to fill with dirt to the depth of about 20~30cm. The ground is now a very hard clay in some areas, mud stone in others.
The plan is to lay some ag pipe connected to the storm water system on the low side then lay a base on top of that, then put top soil on top of that. Grass will then be planted.
What base should I use - sand, gravel,....?