Burial vaults (grave liners or grave vaults) are boxes fabricated of steel, plastic, or concrete that are intended to encase the coffin and support the soil over the grave. The soil will settle over time from the decay and collapse of the coffin or shrouded body, the weight of heavy equipment used to open / close nearby graves, or the weight of foot traffic. This ground settling is problematic for the cemetery lawn mowing equipment, monuments, and visitors. Most conventional cemeteries will require the use of a vault to avoid these issues. Green burial grounds do not permit vaults, and will usually backfill the graves with soil from the original hole as need requires.