Inground swimming pools come in three different types: concrete, fiberglass shell and vinyl liner. All three types of inground swimming pool can be made with a variety of options, including pool steps that allow swimmers to just walk into a pool. Regardless of the type of swimming pool, anything like a set of steps must be supported from behind by using a backfill. Backfill works to support swimming pool steps by providing the actual support against the weight that presses on them.
Inground swimming pool builders use three types of backfill: dirt, sand or gravel. Dirt and sand backfill for swimming pools take some work to properly compact so that it lasts a long time. Gravel, on the other hand, compacts very easily and is extremely efficient at draining groundwater away from a pool. For in-ground pool steps, the excavated pool hole is shaped to form steps where needed, with a backfill base laid to support those steps from behind.
Two different types of gravel are used as backfill for an in-ground swimming pool: #89 stone and #57 stone. The #89 stone gravel is also known as pea gravel, and it's excellent for use as a backfill behind pool steps. The type of gravel used as a backfill behind pool walls is #57 stone, which is rougher and larger than #89 stone gravel. The #89 stone gravel goes behind pool steps because its small size allows it to be tightly packed, eliminating any air pockets.
Gravel is more expensive than dirt or sand when it comes to use as an inground swimming pool's backfill. It can take weeks or even months for dirt or sand backfill around an inground swimming pool to sufficiently compact. All pool steps require some sort dirt, sand or gravel backfill to support them because they're relatively structurally weak on their own. Dirt or sand backfill behind pool steps is "washed in" several times and compacted by the weight of the pool's steps.