Coffins are built so that they do not collapse when they are initially buried.
Over time, environmental elements, and decomposition will cause the casket to collapse under the weight of the soils above it. This can cause the soil at the surface to sink, a process known as grave subsidence.
This article examines the factors that cause a coffins and caskets to collapse, the causes of grave subsidence, and the use of outer burial containers in the United States.
Why a Coffin Collapses after It Is Buried
A coffin is typically buried several feet underground to prevent humans or animals scavengers from disturbing the grave.
Once the burial ceremony has been completed, cemetery personnel cover the coffin with soils from the excavated area, gravel, and/or sand. The replaced soils are not fully compacted, as doing so would cause the coffin to collapse.
A coffin is built to withstand the pressures of the soils above it, and remains intact for many years. However, a coffin buried in the ground will eventually collapse under the pressure of the soils above it for a number of reasons:
- 1. Decomposition and Degradation:
Coffins are made out of a number of different materials, including wood, steel, copper, and bronze. As the coffin sits underground, the wood will begin to decompose, and the metal will rust, thereby weakening the casket structure.
- 2. Natural Elements:
A coffin underground is surrounded by natural elements that can negatively affect its integrity.
- The pH of the soils can speed up decomposition and degradation.
- Rainwater and groundwater can seep through the soils around the casket, causing wooden coffins to slowly rot and metal caskets to rust.
- Plant and animal life, such as microbes and plant roots, can slowly degrade the integrity and stability of the casket walls.
- 3. Time:
Most caskets are left in the ground indefinitely. Like all man-made things, they cannot withstand the forces of time, and will slowly degrade when left untouched.
The exact amount of time it takes a casket to collapse varies based on a number of factors, including the nature of the backfilled material and surrounding soils, the frequency of contact with the elements, and the craftsmanship and material of the casket.
What Happens When a Coffin Collapses
When a casket collapses, the soils above enter the coffin, causing the surface above the coffin to sink. This phenomenon is called grave subsidence.
Grave subsidence can also occur as the air pockets in the non-compacted soils above the casket escape, and the soil settles.
The amount of gradual grave subsidence that occurs when the soils settle varies based on a number of factors, including the:
- Nature of the backfilled material
- Nature of the surrounding soils
- Depth of the excavation
- Amount of rainwater or groundwater in the soils
- Grave location
- Number of people buried within the grave.
The biggest problem with grave subsidence is the challenge it presents for cemetery employees. Grave subsidence causes depressed areas in the cemetery, which can be dangerous trip hazards for visitors and maintenance machinery. It can also cause tombstones and plaques to shift and break, creating emotional distress for family members and additional maintenance expenses for the cemetery.
Grave subsidence caused by the settling of the soil is combatted by initially overfilling the excavated area. When walking through a cemetery, you can identify new graves by the mounded dirt. However, when a casket is buried directly in the soil, there is not any easy solution to prevent the grave subsidence caused by the casket collapsing.
How Grave Subsidence is Prevented
Many cemeteries in the United States use outer burial containers, such as grave liners and burial vaults, to prevent the grave subsidence caused by caskets collapsing.
Outer burial containers are specifically made to protect the casket from the pressure of the soils and cemetery maintenance equipment.
In the United States, most outer burial containers are made of concrete or reinforced concrete and are installed along the edges of the excavation. The cemetery determines the type of outer burial container required. The most common types of outer burial containers are the following:
- Grave Liner/Grave Box:
Grave liners are typically made of concrete, a naturally porous material that allows water and soils to flow freely in and out of the grave.
Grave liners are required to have walls and a lid; however, they do not always have a bottom. Most grave liners also have holes in the bottom and/or sides to allow groundwater to flow in and out of the grave.
Grave liners are typically the cheaper option if an outer burial container is required.
- Burial Vault:
Burial vaults are typically made of concrete with an interior plastic or metal lining to prevent soil and water from entering the grave. The addition of the interior lining ensures a dry, preserved space for the casket, which can slow the degradation of the casket and body.
Because of this added layer of protection, burial vaults are more expensive than grave liners.
If an outer burial container is used, it is installed in the grave prior to the burial ceremony. During the burial ceremony, the coffin is lowered into the outer burial container and the lid of the container is closed, thereby sealing the casket within the burial container.
Caskets do not collapse when they are initially buried. However, there is no way to prevent a casket from eventually collapsing when it decomposes or degrades.
While outer burial containers do not prevent the degradation and eventual collapse of the casket, they can help cemeteries prevent the grave subsidence that can result.