ASCE 24 and an In-Ground Swimming Pool

[phamENG]

Good evening everyone. Quick question to see if anyone has dealt with this before. I have a potential client that has approached me about a swimming pool being installed in a coastal high hazard area. It's a fiberglass pool. The intent is to go with go with the clause in ASCE 24 that states that the pool has to remain in the ground during a design flood event. I'd be designing the restraints to keep it in the ground.

I can go really conservative and assume that the pool is bone dry when it floods and thus use the full volume in the buoyancy calcs. It may not be too far off - around here people tend to pump down there pools for maintenance and cover them between labor day and mid October, so that leaves a solid month of Hurricane season and a fair chance of a flood event hitting once the pool is closed (I'm looking at you, Disturbances 2 and 3...).

What about hydrostatic relief valves? Are they reliable enough to count on them for something like this? Seasonal groundwater fluctuations, sure, but I don't know about a major flooding event.

How about tie down attachments? Anyone ever detail that for a fiberglass pool? I'm guessing the concrete skirt is supposed to help, since it's the only thing that can really be embedded in concrete, but I'm not really confident in the ability of the joint to remain if it's actually put to the test.

If anyone has any personal stories to share or industry standards that they're aware of, I'd be grateful. I've initiated a conversation with their manufacturer, so that may help.

Thanks.

 

[Tomfh]

What about hydrostatic relief valves? Are they reliable enough to count on them for something like this?

They sure help, but groundwater could rise faster than they can deal with. They can also block or otherwise misperform. They're useful things. My pool has been empty for 3 months and it's been interesting seeing the hydrovalve open in the days and weeks after rainfall. You get a good insight into the water table that you dont otherwise see.

A lot of fibreglass pools have dewatering system around the pool and sump pump to prevent the water from building up in the first place.

Once any ground water has built up these plastic pools will generally fail anyway. They're not designed to function as a boat. They need water/soil both sides of the shell. We're dealing with one at present where the walls caved in after a pool painter came and drained it. That's quite common.

I don't know if people actually anchor them down so they could never float no matter what happens. Seems pretty drastic.

 

[StrucPatholgst]

Food for thought: I have a client on a bay front parcel with a large inground pool. It's a fiber glass shell set in a large, mounded mass of concrete that reaches up to the lip of the shell. The concrete mound is surrounded on the bay side by rip rap. A nuclear bomb couldn't move that thing. And the bay laps right up to the rip rap. Also, there is supposedly a large number of driven timber piles under the mound of concrete.

 

[phamENG]

Tom - thanks. The rate of pressure buildup is what I was worried about there. Nice to hear some first hand experience. As for the anchorage question, it's less about not damaging the pool as it about protecting surrounding structures. If it pops out of the ground it could float and it could slam into the neighbor's house. No good. So ADCE 24 requires that it be anchored.

StrucPathologist - the lip of the shell. Did you do any sort of analysis for the interlock there? What approach did you use? Sounds like an interesting install for a pool.