What material should not be used when protecting buried conduit during backfilling?

The selection of materials used for protecting buried conduit during backfilling is critical to ensure the integrity and longevity of the installation. Large rocks are inappropriate for this purpose because they can exert significant pressure on the conduit, especially when the soil settles. Such pressure increases the risk of physical damage to the conduit, including crushing or deformation, which can lead to operational failures or costly repairs down the line.

In contrast, silt, fine sand, and clay can all provide better support and protection for the conduit. These materials have finer particles that can conform more easily to the shape of the conduit, offering a cushioning effect and reducing the chances of direct load impact. They also tend to compact well, which helps to secure the conduit in place and minimizes movement that could result in damage.

Using materials that are too coarse or have sharp edges, like large rocks, is generally discouraged in construction practices focused on buried installations. Therefore, the use of large rocks is deemed unsuitable in protecting buried conduits during the backfill process.