New twist to in ground pool failure

[brusky100]

I am a PE and investigated an in ground pool failure where the pool cracked and slightly lifted after a piping failure to the pool heater resulted in emptying the pool in less than 8 hours and the damage occurred that same day. The water released went away from the pool (backyard) to the front and street drains. The elevation of the pool at the rear of the house is higher than the rear boundary which is a golf course. The house has gutters installed directing water away from the pool area.

This occurred in December and there was negligible rain during the month and in Florida this is the dry season of the year.

During the same day, the barometric pressure declined during the dag from 30"Hg which it had been for most of the previous month to a low that day of 29.6"Hg and rebounded the next day to 30.2"Hg.

Usually these events are a result of ground water pressure. Is it possible that the failure could be attributed to increased lateral pressure from surrounding ground fill which was in equilibrium the filled pool, but not when emptied?

Also, would the atmospheric pressure difference be a contributing factor. For a 30"x 15" pool, the reduction in atmospheric pressure noted above is approximately a 28.3 psf or 12,735 lbs. Of course, the water weight removal is over 10 times in magnitude.

Thanks in advance for your opinions,

 

[hokie66]

Atmospheric pressure, no. Lateral pressure, no. Hydrostatic uplift, yes. Not all of the water went away, some went into the ground, and along with ground water that was already there, the pool floated.

By the way, I assume you mean the pool is 30' x 15'.

 

[brusky100]

Yes, the pool is 30' x 15'. The leak in plumbing occurred at the heater where the line uncoupled. This is on the other side of the house AWAY from the pool and the discharged water did NOT go anywhere near the pool. The one side area of the pool that cracked along the bottom and side wall and lifted was a longer wall area on the shallow area of the pool that was less than 4' deep. The deep end of the pool ~ 8' had no cracks, damage, or uplift.

 

[hokie66]

There is water in the ground under most pools. That is the reason they should have hydrostatic release valves in the bottom, in case of deliberate or accidental emptying.

 

[brusky100]

As I said before, the deep end of the pool and other shallow sides had no lift, cracking or damage. Only on one longer shallow pool wall was there a crack along the bottom and that side lifted. The pool has a large concrete deck and patio which is screened in. The ground profile behind the house has a lower elevation with golf course. A lake about 200 yards from the house had a lower than normal level and is about 10' below the house elevation.

It may be that the rapid emptying of the pool (around 4 hours) caused a stress crack in the shallow bottom that leaked water into the ground that then caused the damage as the other pool areas had no damage. It was 4 months after the event that I observed the damage. Also, the opening in the deck would have allowed rain to penetrate along that side of the pool after the initial damage.

What happened when is the real question.

See the attached pics.

 

[hokie66]

Why is it important at this stage to know the exact sequence of failure? If you know the pool broke its back due to the sudden emptying, anything else would seem purely academic. Or is there something else involved, e.g. the insurer asserting that the pool was latently defective?

 

[brusky100]

It relates to what exclusions apply from the insurance policy. Such as:

"water below the surface of the
ground, including water which exerts
pressure on, or seeps or leaks through a
building sidewalk, driveway, foundation,
swimming pool or other structure."

Further, the surface of the ground is ambiguous in that there is structural fill put in place to support the concrete decking. For example, what is the surface of the ground under a building that has a perimeter foundation that increases the interior slab height some 2 feet above the original ground level with structural fill? Also, what is the surface of the ground under a highway that has structural fill and crushed rock placed under the asphalt base?

 

[chicopee]

This story is somewhat confusing and not well described by a PE, however, by gathering the relevant piece of information, I think that the pool cracked initially on the shallow side and water filtered thru the crack created an unevenness in the pool bottom. This unevenness strained the bottom retun pipe and thereby causing a separation of the piping connection to the hot water heater.

 

[cvg]

a) regional groundwater level? - you seem to indicate it is below the pool
b) pipes buried below pool - they always leak causing elevated groundwater in vicinity of pools
c) pump broke and somehow the pool drained. - I assume pipe returning flow to the pool broke and water drained to front street
d) pool drained quickly and because of item b), there is now an unbalanced force on the pool
e) shallow end drained empty first
f) shallow end then cracked, relieving the stress
g) deep end then continued to drain out

 

[dicksewerrat]

If the water table were above the bottom of the shallow end, it would still be flowing. I think you have to look at the soil in the area of the uplift.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[cvg]

no, it would not still be flowing. groundwater level in the vicinity of pools is caused by leaky piping under and around the pool as well as by cracks and gaps in the plaster. this is common around nearly all pools. once the pool drained and the pump was broken, the pool drained and the water source was shut off. the ground dried out and after 4 months later, there may be no evidence proving how high the water table was.

 

[hokie66]

brusky100,
I don't know which side you are representing, but without reading the whole policy, I believe the exclusion would apply. The "surface of the ground" is where the ground is on the day, not where it was at some time in the past. If damage due to water below the ground is excluded, the insurance company will not pay.

 

[hokie66]

Modifying that opinion somewhat, the argument of the pool owner should be that the damage is due to the broken pipe which is above the ground, not to water below the ground.

 

[brusky100]

Broken pipe was away from the pool and the discharged water went even further away from the pool. The pressure relief valve was opened the day of the event and the equilibrium level was less than 2 feet in the deep end when photo taken within the month. I included pictures earlier. The insurance company engineer said the pool couldn't drain in less than 5 hours with an open line (pipe break on the supply side)

"The report is deficient in its factual information as it says on pgs. 24 and 25 that the turn over of the water in the pool is about 4.5 times in a 24 hour period ignoring the loose line to the heater. It then “quibbles” and says it is impossible for the pool to drain completely within a 5 hour period."

I contend that when you disturb the surface of the ground to place structural fill, you have altered the ground surface and this provision in the insurance policy becomes ambiguous.