Hi, we’ve recently installed a retaining wall at 400 mm in height . We need to bring the soil level up 400 mm, and lay new turf.

My question is regarding the best product to use for back fill, as there is quite a lot of backfill required. Wondering if we should use some road base first for the first 200mm then soil fill?Then prep for grass?? I don’t want the lawn to drop once it’s settled , so not sure about the road base .