How Much Soil on Top of Builder’s Rubble

Question

My builder has raised garden with rubble from house and is going to put soil on top and then grass. How deep should soil be, as I have a lot of plants in big pots that I want to put in the garden. Also, how can I prevent it from sinking, as I live on a hill.

Answer 1

I highly recommend placing about 18 inches of sand down first and lightly water it in. The sand will help to fill the voids that typically exist with rubble. The big problem is that the rubble creates what is called bridging and over time with the weight of soils and such above, the bridged items can just let go and drop anywhere from a few inches to a couple feet! Depends on how big the void area is under the bridged rubble. It is best to put down layers of soil or a sand and pea gravel mix between layers of rubble as this helps fill and eliminate the voids that cause bridging. You will likely need three to four feet of soils on top to have plenty of depth to be able to plant large shrubs or trees well. If the rubble is already dumped into the area concerned and was not layered in with either the soils of sand and pea gravel mix, there is no real way to prevent the settling. It can be very problematic as you never really know when and where the bridging will let go and create a sunken spot. Have a pile of good soils somewhere so you can peel back the sod or move items from the garden, fill in with soil and compact. Then lay the sod back over the spot, tamp lightly and water well. I hope this all helps you. Best of luck to you too.