Helical Piers for Swimming Pools 1

[flyfish400]

Would it be advisable or inadvisable to use Helical Piers to support a large residential swimming pool? Would this create stress on the pool if the ground shifts or would it prevent stress if the piers were tied to the walls with stee?

 

[RiBeneke]

By helical piers do you mean piers in the shape of spiral staircases ?
Supporting the pool from underneath ?
I don't quite understand.

 

[flyfish400]

I am told that the Helical Piers are steel piers with a helix for driving them into the ground. The pool is new construction. I haven't seen them used before, but am told it might be a good idea. They are placed on 8 ft centers and are tied with steel to a 12" X 12" beam around. Helical Piers can be seen at "helicalpiers.com" They are reasonably expensive- $300-$400 per pier, so I don't wish to use them unless it's necessary. A contractor recommended them, but again, I'm not familiar with their use, the advantages and disadvantages from a swimming pool structure perpective.

 

[LPPE]

Are you on the shoreline where your pool has to be above a flood elevation, therefore above grade? Or just poor soil conditions where your pool is going? Most inground pools dont require piles. Sounds fishy to me.

 

[flyfish400]

It's a fairly large pool, L shaped- 40 ft X 44 ft. This is an in ground pool but the area is noted for some poor soil conditions. Lots of clay - drainage can be an issue, Texas heat and droughts, etc. With soil movement, I was trying to determine whether or not you would want the pool to float or be tied to piers.

 

[RiBeneke]

I am not an expert on pools, but I think that a conventional in-ground pool is a thin-shelled structure that should float in the ground and move as a unit with the ground if the ground moves.

If the pool is anchored to the ground below, and the clays shrink / swell, then you will induce relatively high stresses at the points where the piers connect to the shell of the pool.

How bad is the soil - can you give a technical description ?

 

[SErgini0]

Working in the swimming pool industry, the structure should be anchored.

There are national standards that must be followed carefully, they also serve as a good guide. If you are in the states, check the NSPI website for information. If you are in the UK, then the SPATA website is the place to go. Note that the 2 institutions are the most recognised and in the case of SPATA it is the national standard for swimming pools.

Look there, you might find an answer. Or post a message at their forums and a specialist in the field will give you more details.

Best of luck!

 

[RiBeneke]

Thank you for adding a well-informed link.

 

[adk]

THis is not really a structural question as much as it is a geotechnical issue. I would have the soil tested by a licensed geotech and have him make reccomendations to you. No two sites are the same and lots of funny stuff can be happening underground. From what I have read TX can have some nasty clay problems.

I have heard of pools incorrectly constructed on clay (I have seen something similar), that the shell can pull away from the deck when the clay gets wet and swells (as the clay swells up and pushes the deck away from the shell which is much heavier and weighted down by the pool). Then when it dries it shrinks, this cycle can destroy the concrete in the deck or crack the pool.

Also, supporting it on piles may not help your lateral earth pressure, which may be fully resisted by the full pool (hydrostatic pressure), it depends on the amount of clay. This means the soil can push inward on the pool walls and crack the concrete, if not designed properly.

Bottom line get a geotech (I am structural eng. and value there opinion), and a good pool warranty. I would think your pool contractor would either need to get a soil test or would want one if he is reccomending something this serious.