# Above Ground Pool Collapse

• posted on June 28, 2005, 2:55 am
Hi,
Neighbor's above ground pool collapsed inward while they filled it with water.
Just curious if anyone has heard of the experience before. I did not participate in the pool construction, but I did help with one, years ago.
I recall gravel on exterior of circle, but I still can't figure out from physics perspective how the pool would concave unless there was some stress bearing part of side-wall/top which was not secured. I do recall when doing the liner that there were instructions about how the edge of the bottom of the liner needed to be a certain way. I am thinking the liner edge on bottom of pool was mis-alinged and some how applied pressure to the side, above the bottom of the pool. A theory.
Any thoughts?
Just curious.
Thanks.
j
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• posted on June 28, 2005, 2:52 am
Dont buy an above ground pool.
HTH
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• posted on June 28, 2005, 12:30 pm

EZ-Set pools seem nice, with the air doughnut at the top... 12'x36" for \$98, 14'x39" for \$159, 16'x42" for \$218, 18'x48" for \$297, at Wal Mart, including a ladder and pump and filter.
They might last a long time, away from people and out of the sun.
We might put a 12'x3' pool inside a 16'x16'x8'tall greenhouse with 5 \$7 doubled 1x3 bows on 4' centers and stretch 2 \$20 16'x25' poly film layers over a \$20 layer of 80% shadecloth over the bows and trickle water between them with Grainger's \$157 4RD12 pump, collecting 0.8(620+1000)8'x16' = 165.9K Btu and losing about 6h(130-34)201ft^2/R1 = 115.8K Btu on an average January day in Phila, for a net gain of 50.1K Btu/day.
If it supplies 50K Btu/day over 5 cloudy days and 250K = (130-110)P, it needs P = 12.5K pounds of water, 12.5K/62.3/pi/6^2x12 = 21" deep. We might float a 10'x1" foamboard disk on top that supports a 300'x1" \$60 HDPE pipe in a flat spiral to heat water for showers, and surround it all with 2' of mulch or bags of dry leaves.
Nick
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• posted on June 29, 2005, 7:34 pm

And cover the pool surface with a 9'x2" foamboard disk supporting a \$60 300'x1" flat pipe spiral, with a 12'x12'x2" layer of foamboard over that, and mulch around the pool up to the foamboard, with whitewash over (how much of?) the north wall of the greenhouse. The 2x2'(12'+16') = 112 ft^2 of mulch surronding the horizontal collector would act as a parasitic air heater, warming the air around the collector and reducing its loss.
Nick
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• posted on June 30, 2005, 3:27 pm

The pool comes with a filter and a 540 gph pump. With no filter, it might push water up a few inches above the water level. With 130 F water, it might need a cooling air supply, eg a small hole in the greenhouse near the ground and another near the peak.

....and black fiberglass window screen over that, and poly film over that. A separate fountain pump might move a little water over the top of the film to prevent overheating in summertime. Outdoor air with w = 0.0133 in July in Phila makes Pa = 0.626 "Hg. At 130 F and 100% RH, Pw = 4.74 "Hg, so a wet square foot might lose 100(Pw-Pa) = 411 Btu/h by evaporation, more than the peak solar gain.

....about 4 feet above the collector, to reflect more winter sun onto it.
20 PI=4*ATN(1) 30 WC'N-S collector width (feet) 40 LC'E-W collector length (feet) 50 HC=3'collector height (feet) 60 AC=WC*LC'collector area (ft^2) 70 RCC=1'collector cover US R-value 80 RC=RCC/AC'collector-greenhouse thermal resistance (F-h/Btu) 90 WG'greenhouse width (feet) 100 LG'greenhouse length (feet) 110 HG=8'greenhouse height (feet) 120 FOR HR=6.9 TO 7.1 STEP .1'reflector height above ground (feet) 130 WUC=WC/2+SQR(HG^2-HR^2)'unshaded collector width (feet) 140 AGC=PI*16*16/2+PI*8^2'greenhouse cover area (ft^2) 150 RVG=.8'greenhouse US R-value 160 RG=RVG/AGC'greenhouse-outdoor thermal resistance (F-h/Btu) 170 GHGAIN=.9*(WG*620+HR*1000)*LG/6'Jan gh gain (Btu/h) 180 CGAIN=.9*(WUC*620+.9*(HR-HC)*1000)*LC/6'Jan collector gain (Btu/h) 190 SACGAIN=GHGAIN-CGAIN'sacrificial heater gain (Btu/h) 200 TA4'outdoor temp (F) 210 TP0'pond water temp (F) 220 TGAT=TA+SACGAIN*RG'Thevenin gh air temp (F) 230 CLOSS=(TP-TGAT)/(RC+RG)'collector loss (Btu/h) 240 CNET=6*(CGAIN-CLOSS)'net collector gain (Btu/day) 250 PRINT HR,"Jan (Btu/day):"TAB(35);CNET 260 NEXT
reflector height
6.9' Jan (Btu/day): 57521.07 7.0' Jan (Btu/day): 57581.57 7.1' Jan (Btu/day): 57579.94
With Pi(7^2-5.25^2)3/27 = 7.5 cubic yards of mulch or bags of leaves inside a 14'x3' welded-wire fence circle (which would provide some pool reinforcing), 16.4K pounds of 120 F water might lose 5dx24h(120-34)(100ft^2/R24+64ft^2/R20) = 75.8K Btu and provide (16.4K(130-110)-75.8K)/5 = 50.4K Btu/day of hot water for 5 cloudy days in January.
Nick
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• posted on June 28, 2005, 3:10 am
Hi,
I just never heard of this defect. Good advice, but you should see all of the above grounds which go up in the 'burbs. The air inflated ones appear to be popular these days, too.
I don't think most middle class wage earners can afford a below ground pool and the option for above ground looks normal friendly to the pay check. I am guessing.
j

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• posted on June 28, 2005, 7:08 am
Hmmm, where did the water go? Tom
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• posted on June 28, 2005, 11:05 am
That is the ugly part. Inside the collapsed pool.

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• posted on June 28, 2005, 11:02 am
Yes, what probably happened was the liner shrunk from being exposed to the sun for too long while empty. Then when you filled it, it ... did what you said.
I made that mistake once. Never drain it fully, try to never drain it at all if possible. Also saw it happen to my neighbor... Must be a common problem.

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• posted on June 29, 2005, 2:31 am
Thanks. That makes sense.
I will need to find out if they waited untill next day, or did not follow guidelines to be sure liner is sitting on edge of bottom as water fills in. I recall that initially you need to be in pool making sure liner is tucked in as water level builds up and applies pressure.
j

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