I'm thinking about my next photobash. I've seen photos of projects turning old, likely nonfunctional swimming pools into walipinis, but conventional wisdom has that there's a big difference between an empty concrete swimming pool and a proper foundation. That the sides will collapse without the support of the pool water, or the water table in the ground will lift the thing like a concrete boat and break it. Just the same, it's not uncommon to see abandoned swimming pools laying empty, looking more or less foundation-shaped. It seems like a very solarpunk thing, to turn an expensive-to-maintain luxury into something practical, a greenhouse that takes less energy to keep it warm.
So my question is: can it be done, especially if the pool is already nonfunctional and you're not worried about returning it to its original use? What steps/precautions should you take to make it last and safe? Reinforce the sides? Cut away part of the bottom? Add drainage around it?
Thanks for any thoughts
Swimming pools are normally constructed empty. They were withstanding surrounding soil before they were filled, and concrete strength increases with age (for about 90 days, typically). On the other hand, a sunken structure like a pool that is roofed over, becomes a "confined space". Unlike a typical structure, heavier-than-air gases cannot escape from the pool. Such gases could originate from the drain system or flow from leakage outside the pool area. For examples, leaking propane or various gases from sewer lines in the vicinity. A sunken greenhouse would almost certainly be a building code violation for that reason. If you build it, ventilate it by means both active and passive and do not enter if you can't verify that ventilation is working.
That's a good consideration and something I haven't seen brought up with regards to walipinis (didn't think of it either, though I had read up on the risk awhile back for a postapoclyptic story I was working on about a guy who hunts for old bunkers and safe houses). Nature abhors a vacuum and it likes to fill them with water, mold, and heavier-than-air gasses. Luckily, greenhouses require a certain amount of ventilation, but I doubt most are configured properly for heavier-than-air stuff. Thanks!