Why does a swimming pool need to be backfilled? Why does it need a base plate?

A swimming pool built into the ground must, on the one hand, withstand the pressure of the soil from the outside. On the other hand, the pool must not be deformed outwards by the water pressure on the inside. Since a GRP pool is basically an elastic plastic body, it is not readily capable of withstanding soil pressure or water pressure on its own. This task is essentially performed by the backfill. The material and thickness of the backfill must be chosen so that the aforementioned pressures can be absorbed. To prevent the backfill itself from shifting, it is "spread out" in the area of the pool floor by building a concrete slab between the backfills. To prevent the backfill from deforming in the upper area, a ring beam is placed on top of it. The entire backfill construction therefore consists of three elements: floor slab, backfill and ring beam. The resulting overall construction provides so much strength that the pressures from inside or outside are absorbed. In addition, the coping stone and the paving around the pool then also have a permanently solid support.

In some federal states, structural engineering calculations for this construction are required as part of the building permit for pools, and are available on request from the pool supplier or the backfill system supplier.

A note: As shown above, the floor slab is subjected to "compression". This is the reason why the floor slab only needs to have a thickness of 10 cm and does not require steel reinforcement.