subject to the code official’s approval, provided none of
the following conditions is encountered at the site:
at desired slopes.
(This is the main reason that Fiberglass pool shells are recommended in the sandy soil areas. If the bottom is prepared not to liquefy if water comes in contact then placement can be made and the shell supported. It can be very expensive during and after construction of a vinyl pool if the soil will not hold shape. A foundation would need to be made to place panels of the vinyl pool on. Other construction materials would need to be brought in to hold the sloping walls in shape. Engineering of how much material to be used and also dimensions are necessary to provide an adequate construction.)
(I believe that this may be something encountered in rocky areas. But if the sand bedding cannot be confined it would need to be engineered to show support structure)
The ICC has stated a certain acceptance level of where a RDP is needed but unfortunately in our industry this is not adhered to and not known by either the code officials or by the builders. This is something that can add cost to the initial purchase of a vinyl pool as well. The best protection is to work with an experienced builder that is knowledgeable in the common area soils. Work with a licensed Swimming Pool Contractor. If your builder does not know about clay or expansive soils or can tell you what he will do and how much it will cost if unstable ground is encountered, run away and find a capable builder in your area. It is wise to spend a little more and save lots later on.