As I was doing research recently on vinyl liner fungus I came across the International Code Council (ICC) Acceptance Criteria for Vinyl-Lined Residential Swimming Pools (AC279). I found some of the information very interesting. This is not information that most builders, retailers or customers ever see but I find some of it very important. Of special interest to me is section 5.2 which states:

5.2

Pools and spas may be installed without a soil

investigation by a registered design professional (RDP),

subject to the code official’s approval, provided none of
the following conditions is encountered at the site:

(In most states a Registered Design Professional is an engineer or architect that has been certified and licensed by the state)

5.2.1

The existence of groundwater within the depth

of the pool or spa excavation.

(This would lead us to believe and we would be correct in assuming that once you excavate and find there is groundwater then an RDP needs to do a soil investigation to see that your structure will uphold under the soil conditions. This cost could be hundreds of dollars. I do not know of any builder of residential pools that does this. Nor have I seen any code inspector inspect the excavation to enforce this. However in years down the road and excessive underground water at any time the pool structure can be compromised causing major repairs. I have seen this often in the area in which I serve which is a coastal community with sandy loom soil. As shown through a school science project and shared to me by the parent who happens to be a well versed scientist, sand when wet liquifies therefore no longer bein a supportive foundation. This can cause vinyl liners to have "sink holes" regardless of compaction during construction.)

5.2.2

The existence of an uncompacted fill in

contact with any portion of the pool or spa.

(Again, generally there are no inspections to test for uncompacted fill, this would be solely at the builders or homeowners descretion)

5.2.3

The existence of any expansive-type soils.

(Clay as a soil or mixed in as part of soil is called an expansive soil and is responsible for many home foundation failures. This expansive soil can cause structural problems when used as back fill for many pool types. In our building of pools, clay is trucked away and other acceptable back fill is brought in. However there is usually an extra charge to the homeowner as we are doing it the correct way. Again, not knowing this as many new installers or those without proper training can cause premature failures of the pool structure. See Expansive Soils)

5.2.4

The existence of any soil types with an angle

of repose that will not support the walls of the excavation

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.)

5.2.5

Danger to adjacent structures posed by the

proposed pool or spa location.

(Most code officials check placement of pool to be out of the area of repose of a 45 degree angle from the foundation of adjacent structures taking into account the depth of pool or spa. This is why engineering is required if you place the pool or spa directly next to a structure that is not on piles.)

5.2

The existence of any cracks or openings in

soil that would not confine sand bedding.

(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.