Burial Vaults (also "Outer Burial Containers")
Most cemeteries require a receptacle to place the casket in for burial. Their primary purpose is to support the soil. The minimum requirement is usually a concrete box, but other options are metal and fiberglass. When the body will be entombed in a mausoleum, the cemetery does not require any container beyond the casket.
Types of outer burial containers include:
It is unlawful under Federal law for a funeral provider to tell a customer that outer burial containers are required by state or local laws, or by particular cemeteries if such is not the case. Generally, outer burial containers are not required by state or local laws, but they are oftentimes required by cemeteries to prevent the grave from collapse.
Click here to read the rest of the article from Funeralwise.com