This isn’t going to be fun?

[Bill1974]

That's surprising and disheartening to see. was there anything that was unique/special to the area that is raised? Tough to see if everything sunk or just the one area heaved. I would think everything sunk except one area. Maybe the fountain was constructed so it would not sink/settle. when pumping water from under the pool did it come out muddy or clear?

I can understand trying to pump out the water as fast as possible but removing the water to quickly from under the pool may have been a contributing factor. May also be that the fill under the pool is settling into the native soil under it.

I don't think there is anything you have done wrong, its more so with out the excavation was done, native soil compacted, back fill material and how it was compacted as well.

 

[gonegolfing]

That's surprising and disheartening to see. was there anything that was unique/special to the area that is raised? Tough to see if everything sunk or just the one area heaved. I would think everything sunk except one area. Maybe the fountain was constructed so it would not sink/settle. when pumping water from under the pool did it come out muddy or clear?

I can understand trying to pump out the water as fast as possible but removing the water to quickly from under the pool may have been a contributing factor. May also be that the fill under the pool is settling into the native soil under it.

I don't think there is anything you have done wrong, its more so with out the excavation was done, native soil compacted, back fill material and how it was compacted as well.

I’m the furthest from an expert there could be but I’m pretty sure there has been minimal sinking if any. We eagerly await confirmation from the paver guy we used. If you look at the first pic in post #1 doesn’t that confirm a “heaving” ? I don’t think the pavers would break that way if there was a large sink - if that even makes sense?

No, nothing unique to that area as far as I know. There is nothing too fancy about the fountain construction - it is as it looks - makeshift travertine box with the fountain screwed on top.

The removal of water from under the pool has always been done via a siphon using a garden hose (save for the very first time back in April 2021 when the plumber used a pump) which emits roughly 200 litres per hour - water has always come out clean.

I keep thinking about the hydrostatic valve - surely it is/was meant to alleviate the pressure that has caused this ??

 

[Texas Splash]

I keep thinking about the hydrostatic valve - surely it is/was meant to alleviate the pressure that has caused this ??

Yes, to a point anyways. Not knowing all the dynamics about your build, the base, drainage, etc it's hard to know for sure. You described quite a bit of heavy rains, so even if the HSV was trying to alleviate pressure upwards, saturation around or under pool might have still been compromised. Very difficult to know. I would imagine if you get to a point were you lift that pool up and inspect how everything was installed you might get more answers.

 

[gonegolfing]

Yes, to a point anyways. Not knowing all the dynamics about your build, the base, drainage, etc it's hard to know for sure. You described quite a bit of heavy rains, so even if the HSV was trying to alleviate pressure upwards, saturation around or under pool might have still been compromised. Very difficult to know. I would imagine if you get to a point were you lift that pool up and inspect how everything was installed you might get more answers.

Answers will definitely be required before dumping any more $$ on a pool. Without having talked to any so called experts yet, I’m thinking that the pool will need to be cut out by hand - hopefully revealing all answers to help us into the future…..

 

[dleonard1122]

Sorry to jump in here, and I claim ignorance on how insurance differs in Australia versus America, but is this type of thing covered under homeowners insurance?

 

[Bill1974]

Hopefully something other than your wallet covers this.

I find it hard to believe everything settled except around the fountain, but the images of the cracks make it look like that is what happened. But I am guessing it's just the way the photos make it look. If the water in the pool is 6 inches (15 cm) down from the top lip of the pool (and water under it up to the top lip) it's a .22 psi (1.5 bar) pressure differential pushing up on the pool. This is about 300 lb (136 kg) force over a square yard (1M²). I'm estimating the area that popped is 5 or 6 yard² (meter²), which is 1500 - 1800 lbs (700 - 800 kg) pushing up under the pool. Maybe the historic rain also caused water to rush in under the pool and cause the pressure to be higher than a static water pressure.

Ideally not letting water get under the pool would be the best solution. Is there anywhere on your yard that is lower than shallow parts of the pool? If so a french drain under the pool may be able alleviate water from building up enough to cause this from happening again. Trying to pump it out could be futile in a historic downpour.

 

[gonegolfing]

Sorry to jump in here, and I claim ignorance on how insurance differs in Australia versus America, but is this type of thing covered under homeowners insurance?

It is something we are looking into. We aren’t overly optimistic as this whole renovation exercise was done using an owner/builder certificate - we had to sign off on the fact that no one works from a contractor would exceed $19,900.

 

[gonegolfing]

Hopefully something other than your wallet covers this.

I find it hard to believe everything settled except around the fountain, but the images of the cracks make it look like that is what happened. But I am guessing it's just the way the photos make it look. If the water in the pool is 6 inches (15 cm) down from the top lip of the pool (and water under it up to the top lip) it's a .22 psi (1.5 bar) pressure differential pushing up on the pool. This is about 300 lb (136 kg) force over a square yard (1M²). I'm estimating the area that popped is 5 or 6 yard² (meter²), which is 1500 - 1800 lbs (700 - 800 kg) pushing up under the pool. Maybe the historic rain also caused water to rush in under the pool and cause the pressure to be higher than a static water pressure.

Ideally not letting water get under the pool would be the best solution. Is there anywhere on your yard that is lower than shallow parts of the pool? If so a french drain under the pool may be able alleviate water from building up enough to cause this from happening again. Trying to pump it out could be futile in a historic downpour.

That is a fantastic insight. Thanks for that. I am intrigued to find out - when we do cut the shell out - if the hydrostatic valve is in full working order?? The pool is kept very clean and I’ve never noticed what might be remnants of fill that could wash through the valve with the ground water had it ever opened.

The nearest section of our property that would be that low is 30-35 metres down towards the front driveway which includes roughly 15m of concrete. All avenues will be researched for next time - we are just hopeful of being able to come up with a good diagnosis once the shell is removed……

 

[Bperry]

For some strange reason the part of my deck that sank only sank around the fountain, but the fountain stayed perfectly in place and the concrete around it just broke and shifted.