What is another word for backing fill?
Pronunciation: [bˈakɪŋ fˈɪl] (IPA) 
Backing fill, also known as backfill, refers to the material used to refill an excavated area or to provide structural support behind retaining walls. There are various synonyms for the term, such as fill dirt, back dirt, bedding material, and infill. Fill dirt is a popular term used to describe the soil that is used to fill a void left after excavation. Back dirt, on the other hand, refers to the excavated material that is used to fill the void. Bedding material is used for structural support or to level the surface before installing foundation components. Infill is used to describe the material used to fill spaces between walls or floors.
