Groundwater Problems

To repeat the same mistake 3 times seems foolhardy.
I'd suggest that your location isn't suitable for a sunken pool.
Or isn't a pool all above ground level a viable option?

I'm not sure you will be able to pump water away quick enough and where will you pump it to?

Del

Del,

Thanks for the reply, there are other inground pools in the neighborhood and they don't seem to have a problem like mine. The only thing I could do is to pump it to the pavement so that it will get to the storm sewer at the end of the street. The above ground option was one of my choices, and still may be, if the wife wants a pool and I can't work out the sump pump option!!

you could always drill in well points around the pool to pump down the water table. This is probably cheaper than a full french drain to the depth of a pool. However, it seems a bit muchy to maintain a pool. Plus as long as you maintain water in the pool above the water table you should have a net outwater hydrostatic pressure on the liner. With water inside the pool a liner should not separate from the concrete ballast and float, unless you have a gas pocket building up under the liner. Water only seeps in when there is more water outside then inside. Maybe drain your pool at another time not during the hurricane season, and just cover it during the hurricane season.

If the sump pump and the french drains can keep up then what you propose should work; however, put some real effort and maybe a few $ into consulting a hydrology expert about why your second attempt did not work. My experience with french drains is that they do work but that they are slow to drain when challenged with a lot of water.

The problem seems to be that the pressure on the outside of the lining exceeds the pressure on the inside of the lining. Simple, right?

The local university would be a good place to look for a knowledgeable person.

I would not spend a lot of time or $ on the second fix until I figgured out why the first attempt at a fix did not work.

harralrw,

Thanks I'm grabbing at straws trying to figure out what to do! The University option is high on my list. I am a retired landscape architect from the University of Florida and am ashamed, as a professional, for not being able to solve the problem. From my experience as an LA the french drain sump pump idea was the best I could come up with. The bottom line is, as you indicated, the pressure on the outside of the lining exceeds the pressure on the inside. When we dug the pool initially the depth all the way down was high and dry so I don't know where all the water is coming from to cause the hydrostatic buildup behind the walls.

Well I lived in St Augustine 11 years and from what I remember the inground pools need to pump the water at least 25 geet away and the water must drain downhill. I not draining downhill you face constant pumping of the same water after heavey rains.

Most of the people I knew switched to the solid fiberglass pools raised on a berm of sand with a plastic liner under neath and a pump incase the pool was lifted by high surface water or flooding.

They set their pool up on a berm like they do septic tanks out in the county in Fla .

dadw5boys,

I had planned on pumping the water approx. 100' to the street/drainage swales. The problem we had with this last rain event all the swales in my subdivision section were full. That's the reason I thought I could get the water to a non porus surface like the asphalt street. Granted some of the water would make it into the saturated swales but maybe enough of it would make it to the storm drain at the end of the street and I could save the pool walls from caving in.

Is there some way you could tie into your local storm water system? Run your drain lines down to the swale at your roadside if there is one or get permission to hook up to storm water lines.

Dear John,

The only way I would recommend that this person connect to the storm sewer is if a backflow valve is added. Odds are pretty high that during a hurricane the storm sewer system is going to be surcharged. You asking for trouble if a surcharged storm sewer system starts adding water to the outside of the pool.

The poblem with a pump is that you are likely to loose power during a hurricane and then to operate the pump you will need a generator.

I think the owner is best off if the pool walls were designed to handle hydrostatic pressure. Otherwise, the poor guy will be trying to start a generator with all sorts of crap blowing around him. That probably means a concrete wall with a vinyl lining. Get a structural engineer to design the walls - not a contractor.

That is my two cents.

Respectfully Yours,

Christian R. Cooper, P.E., CPESC.

Your right about the backflow valve and a piped underground storm system. Alot of the situations I seen are u-drains leading to a rain garden that when it over flows leads to a storm water system. It's a tough situation he is in. I was thinking of something quick and simple to get the water off the property since the storm-water systems there should be built for 100+ year storm (yeah right).

I'm guessing its pretty much sandy soils and flat, and if the soil is supersaturated and the storm systems are overloaded there is not much you can do. There are also storm water storage systems out there like STORMTRAP (its an underground water detention system)that he could set-up. He also has to watch where he is pumping it to because the next guy down hill is going to get it double.

Just something to chew on

Christian,

In my reply to John I addressed the storm drain situation. The only storm drain in our neighborhood is too far away so I couldn't connect even if I had permission, it's just a matter of $$$$. The pool walls themselves held up to the hydostatic pressure, somehow water penetrated between the walls and the vinyl liner and pushed them into the pool. As a retired landscape architect, I think the pressure was so great that even a concrete pool would have "floated" out of the ground. I have never seen anything like this in my professional career!!!

John,

The problem with our subdivision layout is only one storm drain exists at the end of the street. We do have vegetative swales on each side of the street, no curbs. I am in a cul-de-sac and the drainage is to the storm drain, approx. 800'. The person that laid out the subdivision did it the cheapest way he could. We need more storm drains to get the water off all the properties. I live in a gated community and the home owners association has reluctantly looked at drainage. My particular area is not the only place that has problems. My daughter and her family live 3 to 4 blocks from me and had 2" of water in their house.

Yes, I agree 100% with this post and gave it a GA. The water table is too high and the soil far too porous in most parts of Fl to consider pumping water away fast enough to solve this problem as you suggested. I would suggest the addition of a biocide to the pool water during the off-season period.

Your making the assumption that the pool is empty. Why would you think that?

(note: when it comes to swimming pools in FL, there is no "off season".)

jrpeck,

Thanks, the problem is the subsurface pressure is greater than the pool water pressure. We have such great weather (except with hurricanes and tropical storms) here in Florida that we never drain our pool. We have to maintain it year round.

the problem is the subsurface pressure is greater than the pool water pressure.

Is the water rushing out of ground? Is water pushing up from under the walkways and edges of the streets? Is water pushing up from the edges of your pool? Unless this is happening, your subsurface pressure is not greater than your pool water pressure.

How about this...if you can find it.

Of porthole openings within the vinyl could be placed strategically at various levels around the pool; and if a protective, anti-soil-intrusion screens were fitted behind each porthole; and if removable caps could be fitted so as to close off all portholes during "normal" weather and pool use - then would it not be possible, before a storm event, to simply remove all porthole covers in the pool? And, by so doing...would not any water pressure differential behind the vinyl (on either side) be relieved by permitting water to flow to the opposite side of the vinyl? A self regulating system with no need of "massive" structural and earthworks modifications? Just a bit of pool sweeping after a storm?

Just curious.

I can stand it no longer. If all of the water is exposed to the atmosphere, wouldn't all the water be at the same pressure? Unless there is a pipe shooting pressurized water at your liner, I'm thinking that there is an air pocket that can not escape, pushing the inner liner away from the outer wall.

Is it possible that the top of the wall is sealed to the top of the liner. As the water level in the ground rises, the water seeps past the concrete wall and fills the area between the wall and liner. After the water rises above the last porous area, the air becomes trapped. As the water rises, the air pressure rises. Like putting a balloon over a soda bottle, and then injecting water through a tube passed through the side of the bottle.

Is it possible to vent the space between the wall and the liner?

Bob,

I probably did not make myself clear in the initial Post or replies. The newest pool was put in with resin (polyurethane) walls with a 45 degree support behind the panels, and the bracing set in rebar and concrete. As I indicated the walls did fine. Evidently the panels were put in by sections and there must have been a crack where they butted against each other. This is where I think the water got in between the vinyl and panels forcing the liner into the pool. I have a 4" thick concrete deck poured around the pool and I wouldn't think it would keep air trapped. Also, I used a post hole digger and dug 4 holes around the pool. At some areas I barely dislodged the surface before water was visible. At other holes I went down 6"-8" before water started filling the hole. Hydrostatic pressure must be awful under the deck. I'm still thinking to relieve water pressure around the pool I need to move it to an end of the pool and pump out with a sump pump. Thanks for your comments.

I cannot see how pumping water towards the sea is a foolproof approach. One thing not clear from your OP is whether or not the low pressure system (storm/hurricane) is removing the water in the pool and, of so, to what degree. With Florida topography, it is difficult to imagine sufficient (upslope) head by which ground water pressure (even with water table at ground surface level) would be sufficient to exceed pool head and cause breaching of the pool liner. So it would seem that the groundwater intrusion during (and only during) storm events must be due to lowered static pressure within the pool . . . lowered pressure as a result of emptying of the pool by the storm. This suggests either of two possible solution, each with its own downside:

Depending on pools size, pool cover (as in plates) of sufficient weight and hold-down strength could be used to prevent any pool water loss during a storm/hurricane. Downside: very expensive most likely.

Instead of pumping groundwater away from pool, pump water (either fresh or ground) into the pool until the low-pressure event subsides. . . in order to maintain maximum pressure, and maximum ground water intrusion resistance, within the pool until storm subsides. Downside: providing failure-proof power to run pump during storm event...same as with original idea; and obtaining source from which to pump (it would seem that this must be a well...which might be prohibited by local/state/federal ordinance(?).

That is something else to consider, the Discharge of groundwaters into a storm drain system may not comply with the municipalities NPDES permitting, or if not into municipal facilities may require you to obtain NPDES permitting (or a permit under a State general permit). Wells are typically under local jurisdiction of a Municipality or County authorized through the State, as is excavation. So you would need plans and permits to discharge groundwater and to construct a drainage system.

Tell me if I am speaking like a fool. How is there any difference in water pressure in a pool that is exposed to the atmosphere, and ground water that is rising, also exposed to atmosphere? I can see no way for there to be any water pressure differences. Please explain.

Bob, this is just what my post, #20, was touching upon. If the terrain was such that the water table was higher than the pool (water) surface, then in principle it might be possible for subsurface water "head" to exceed the pool liner resistance when the pool is filled...but it would seem that subsurface water in proximity to the swimming pool must be confined...so that groundwater does not simply flow elsewhere (along a path of lesser resistance) than towards the pool. This is what give rise to the notion (in #20) that the pool (liner) itself becomes that path of least resistance during cyclone events...because the pool is being emptied of its water by the low pressure weather system, and no longer contains sufficient burden of water to resist "wild" water impingement upon the exterior of its liner. For this reason it seemed that some means to prevent the lowering of water level within the pool (assuming the pool is normally kept filled) should also prevent breaching of the pool liner from without...just as during "normal" weather.

Since posting #20 I have tried to think of other mechanisms that could bring about the pools failure...especially those which would occur as "dependably" as Al Stanley (OP writer) suggests. Remembering how Florida's population is concentrated along its shoreline, another coastal feature that has not yet been mentioned also came to mind: the Intracoastal Waterway that runs the length of that state. (The banks of that channel are also a favored site of resorts and upscale houses of the kind most likely to have swimming pools; which might or might not be the case with Al's house and swimming pool.) Figures 1 and 2 below present schematically how it might be possible for coastal storm surges to operate in tandem with the Intracoastal Waterway to bring about localized subsurface pressure sufficient to exceed the resistance of below-ground swimming pools and/or liners.

Legend: Water Outflow (Pressure Relief) Confinements:

1. By saturated soil overburden, swimming pool and pool contents, structures, pavements, pool deck slab.
2. By ICW channel bulkhead and water. Possibly by weight of ocean/beach at time of surge.
3. Gravity and upland subterranean run-off towards sea. Or, same as B. if channel bank (bulkhead) surrounds an island in the ICWaterway.

Comments pro and con are welcomed.

This also suggest a remedy, one borrowed from mining, that might prove less problematic, and would probably prove far less expensive than the hiring of engineering and major underground construction...(exceedingly expensive, in part, because of the risk entailed in warranting such retrofitting against failure in all events....

Depending on pool size, perhaps shoring with panels/plates and timbers/beans, used with floor jacks, would do the trick. With timbers, installation would probably require draining the pool...but the expense of refilling is probably far less that repairing damage over the long term; and there's always the possibility that the storm itself will do much of the re-filling. I can imagine $hundreds, possibly a few $thousands for materials and supplies...but many times that for engineering services and retrofit construction work. Pool wall curvature is a further problem...which could probably be overcome sufficiently with smaller panel sizes and increased number of braces. The braced panels would only need to be close enough to prevent too large expanses of the pool liner from being subjected to encroaching pressures, it would seem. Another problem would be providing storage for the shoring materials between cyclone events. This might be a "quick-and-dirty" approach worth testing, before making a huge investment for excavation and heavy reconstruction retrofit.

You have done a wonderful job of visually explaining the problem. In one of my earlier posts I asked if water was pushing up out of the ground. I would think that if the problem exists as you have drawn it in the second scenario, there would be water trying to force itself up from under sidewalks and other buried objects.

The corrugated black plastic pipe with the 1" holes in it, that is used in underground drain fields might be helpful here. If he was to use an auger to bore a series of holes around the outside of the pool's support walls, then sink the pipe vertically, with the top flush with the surface ground. Place a flower pot on four pavers placed around the opening of the pipe. This should allow any underground water pressures to vent to the surface, and allow the pool to survive.

Now your opinion please.

Thanks, Bob, I'll give it a try; but pending feedback from Al it's hard to know how closely, if at all, my little schematics conform to his situation. We also need to consider the timing elements of the weather event in relation to when it is, exactly, that damage to Al's pool liner is occurring; my sense of the matter is that Al has only seen the liner damage (and the since-remedied pool damage before that) in the aftermath of the storm, not while the damage was actually occurring; that is to say, not at sea surge or wind velocity maximums...the time at which, to me at least, the stresses on the pool would seem to be greatest.

It could well be, as you say, that at some places on Al's parcel water is indeed rising to and above ground surface level...albeit that a concrete patio surround abutting the pool itself would tend to block water in immediate proximity to the pool. Even if that were the case, the additional weight of such water would only add to the burden which the pool wall(s) must withstand...at least until such time as water had overflowed and swamped the pool itself. The reason I did not depict such flooding of the yard and pool is that, in my estimation, the pool liner (as a point of least resistance) was already "imploded" before such a point (of rising water table) was reached, if indeed such a point was reached; if, in fact, surface wind did not "carry away" such surface flooding as fast as it could gather above the pool and pool surrounds.

(If I may interject something at this point, it would be in reference to my earliest post in which I suggested that, rather than pumping water away from the subsurface pool surrounds, pumping water into the pool and overflowing onto the surrounds, so as to flood both the pool and surrounds, might be more effective [and an approach more practical in its achieve-ability] in order, if such pumping commenced early enough, to prevent any pressure differential from arising as between the pool's interior and the surrounding soil. This too, however, would probably not be without its own problem, namely: the simultaneous need to prevent flooding of the house. A house on stilts might do, but houses on stilts [at least those with swimming pools] are not something I recall seeing during my own sojourns in Florida. As to the notion mentioned by Al and others of collecting and pumping subsurface water away from pool and parcel, I would question whether that would have any likelihood of achieving reliable pool protection, considering that there would be nowhere to which the water could be pumped without water flowing (both above and under ground) back towards the pool as fast as it was pumped away! That is to say—and I think my pictures above show this—such pumping would not "gain any [less saturated] ground" until such time as flood waters [and water table] were already receding...and which would probably be too late to have prevented the pool liner damage from being done.)

Finally, about your vertical perforated pipe suggestion—it seems to be a kind of siphon effect that you're going for—that idea suffers (I would say) from the same problem as entailed with previously mentioned attempts to drain or pump water away from the pool. Even if water would rise in the pipes to the point of overflow, where would it then go if not right back down into the soil? Or, if pumped or channelled away...the same problem with water inflow (and rising water table) as fast as water could be removed. A second drawback to the vertical pipe idea is that water "pressure" is a function solely of the (water column's) vertical height component (measured as linear head) and utterly independent of the horizontal component of water containment. This means that the pressure (the weight) of water that flows into a vertical pipe (no matter its diameter) cannot exceed the "pressure" of water remaining outside the pipe; water entering a perforated pipe, then, can rise no higher than the water table within the soil surrounding the pipe; it will not be true that surrounding pressure will force water up to the top of the pipe...at least not until water surrounding the pipe has also risen to the top of the pipe. The idea does, however, share some commonality with Al's (and others') idea of using drain pipes (and gravity/siphoning or pumping) to draw water up and out of the soil...provided (in your case) that the vertical pipe openings were joined to the input of a pump or downsloping, solid drain pipe. But again, we come back to the problem of how it could be pumped or siphoned far enough and fast enough (during peak of rising water) so as not to be "overtaken" by incoming water...so that any net lowering of the water table could realistically be achieved in time to prevent damage.

It is for reasons such as these that, short of major excavation and reconstruction/retrofit, I believe there are two near-term "experiments"—one practical, the other impractical—that might work with some degree of reliability. The impractical approach would entail increasing the depth of the pool by extending the pool's perimeter wall(s) above ground level in order to increase the weight of water and, with that, to increase outward pressure against the pool's lining. This might conceivably be done using plastic sheeting and sandbagging, but it would be very difficult to predict how well such a barrier would hold up against the forces of surf waves and/or hurricane (or tornadic) winds. The more practical (and more predictable) solution might consist in shoring of the pool's interior as mentioned previously. With this approach, once supplies were obtained, the logistics and timing of getting the shoring in place would likely become the foremost challenge.

I think you misunderstood the reason for the vertical pipes. If the Vertical pipes are vented to atmosphere, the ground pressure behind the walls can never be greater than the pressure on the inside of the pool liner, unless he allows the water level in the pool to drop during rainy weather. Won't that keep the liner in place?

There is a technique used in Florida when doing pipe installations when the water table is higher than the level the pipe work needs to be at. A series of 1.5" PVC pipes with small slits in them are driven into the ground surrounding the area that the underground pipes need to be installed, to a depth deeper than the pipes go. The tops of the PVC pipes are joined together to a large volume suction pump with a 6" inlet. The discharge is sent to a storm drain. These pumps are diesel powered, and about 300 horse power. But why seems like he is the only one I ever heard of that has this problem. I have heard of pools popping out of the ground because they were not filled, How do the underground fuel tanks stay in the ground during flooding when they are empty?

This would be similar to a conventional well point system used to dewater underground construction activities below conducted the water table.

You are probably correct. I just don't know what it is called.

Bob, I find myself both enlightened (maybe) and in a quandary based on your response. I had written a reply based on what I understood to be the function of pumping through vertical pipes sunk along the path of a pipeline being installed; and how that might or might not relate to Al's pool situation as you proposed. But reading your post again, I still have a problem understanding what you mean by "ground pressure"; and how it is that open conduits to the surface would relieve such pressure; and how relieving such pressure would benefit rather than harm the pool's, or pool liner's, integrity. Other than water pressure due to adjacent increase of natural head as described in my illustrated post, the only "ground" pressure I perceive would be that imparted by the weight of the pool. The "ground pressure" would be greatest directly beneath the pool, tapering or falling off to nil proceeding upward along the side of the pool walls or (in the case of a bowl shaped pool) pool shell. Such pressure would be essential to support the pool and keep it from sinking. Since anything that would "vent" or otherwise relieve such pressure must also remove the soil as well—by "soil" I also refer to its normal field capacity of moisture—such removals might also cause deleterious effects...by how it affects the normal "ground pressure" needed to support the pool.

Now please read the answer I prepared originally. Naturally, it might only further reveal my lack of understanding...perhaps enough, though, that you will be better equipped to help me understand better. (This conversation about vertical pipes has also put me in mind of another possible "causality" leading to the pool liner problem...one that implicates the previous pool shell collapse, and the buttress work done to repair that collapse, as the reason for Al's subsequent pool liner problem. It also suggests a repair that might fix the liner problem as well...which I will reveal in a separate post.)

Now I think I understand better; perhaps it was the term, vent (as in, liquid and gaseous fluid removal under pressure differential through vertical pipe), that was throwing me.

As I now see it (and inviting your correction), the vertical pipes connected to a 300-HP pump would, in fact, be wells placed strategically for the purpose of evacuating free water (water in excess of soil field capacity) in the soil. The effect of that, as I can perceive it, would be to:

1. Assure optimum (in Fla., most likely maximum) soil compaction and, as a consequence...

2. Maintain soil stability (against fluid [streaming] induced soil movements...peculiar to Florida?

Judging by the massive pumps used, the vertical "well" (and water extraction) piping you described in conjunction with public underground conduit works seems to add an extra dimension beyond the mere sequestering of water in order to stabilize (i.e., firmly imbed) a pipeline: at 300 hp, and by using pipes of small, 1.5-inch diameter, it seems likely that design intention is to pull liquid inward from a considerable distance from each vertical, perforated pipe—in much the manner of a deep water well or even an oil well. This might suggest that prevention of erosion over a considerable distance (i.e., real estate preservation) might be an added feature. I am also curious as to what becomes of the extracted water; whether or not, rather than just being re-routed in its path to the sea, it is being impounded and reclaimed for municipal fresh water supply—perhaps a way to harness and utilize, rather than let go to waste, the frequent, regularly-recurring thunderstorms for which Florida is renowned. Or (in addition), it could be that, if the main pipeline is a water/sewage conduit, then pumping the extracted, natural subsurface water directly from ground into the conduit could additionally provide the motive force...on the way to, say, a water treatment facility.

However, all of these conjectures assume that the "pipe wells" are installed as a permanent feature. Their emplacement could also serve in swampy terrain for the temporary purpose of soil stabilization and back-flooding prevention during pipeline trenching operations—where the confluent "cones of depression" along the trench path (along the series of vertical-pipe wells) extends below the bottom of the trench—with the PVC piping being removed or abandoned in place after pipeline trench backfilling (?). The powering of pumps with diesel engines as opposed to connecting to the electrical grid lends credence to this latter interpretation.

In either event (and assuming pumping), if I understand your proposal (and if, indeed, the "well series" technique finds application other than as a temporary stopgap measure—and leaving aside for the moment questions as to the economic feasibility of such a pumping system to a private person—one possible distinction between the pipeline and the swimming pool scenarios comes to mind. That question would pertain to the effects of configuring the linear well series (as in the pipeline case) as a loop encircling a swimming pool. Keeping in mind that a pumped well's cone of depression extends laterally in all directions...such that, if pumping from a linear series of wells, even if a point of "dryness" between adjacent, vertical pipe wells was reached, a more or less continuous "supply" of water would still extend laterally along both sides of the well series. In an encircling well array, on the other hand, I would question whether or not a point of (non-moisture-replenished) "dryness" within the encirclement perimeter might be reached at which it increasingly became air, or solid soil matter, that was attempting to be pumped (through the perforations in each down pipe). So you might have a case in which one or both of:

• Overall pumping efficiency decreased as air intrusion increased, or
• The evacuation of soil led to gradual subsidence and/or erosion of support for the swimming pool shell (and the buttresses?).

Given a waterproof pavement (rainwater could not leach downward through the swimming pool) within the well pipe encirclement, such a point might be reached even sooner. The question then might be: can the buttressing added to Al's pool compensate adequately...? Or might its own stability (over and above the pool's) and effectiveness be compromised?

Bob, while I'm not yet convince that the passive, vertical-pipe-array idea would work, or that a pumped well array would be sufficient/ reliable/economically feasible, I do see one application where it might be put to good use: to create a water-evacuated zone around the damage area for the purpose of inspection... to see what actually caused the pool skin failure. This could be done either by excavation outside the pool at the site of the liner "blister," or by pool draining, cutting out the blister, inspecting (and removing/repairing), and patching the liner. In Al's stead (I hope he's watching and might consider joining this thread), my initial suspicion (because this liner failure had never happened before) would be that the liner damage was caused by the prior pool shell collapse (perhaps the liner was stretched and weakened), or even by the buttressing retrofit work. Full inspection at the actual site of damage would probably accomplish more than simply determining that the soil is saturated behind/beneath the pool shell...would eliminate a lot of guesswork. It could well be (no pun) that simply patching the damaged area of the liner (after inspecting) will be sufficient to provide the needed permanent fix.

What say you to this? Am I now even farther from understanding?

CA

First lets separate the well point pump system. The only reason I brought it up was because the opinions posted on this thread would lead one to believe that it is not possible to lower the water table here in Florida. It is done every day.

In post 15 alstanley states subsurface water pressure is greater than pool water pressure. I contend that it is not subsurface water pressure, but subsurface air pressure. I present the following information for consideration.

1 The normal water table in this area is low enough that the construction company was able to build a pool. The OP is in north, central Florida, there is no inter-coastal waterway in that area. There may be canals, lakes, and rivers, but these should all be at lower levels than the ground the pool is built on.

2 The pool is never drained. That is also stated in post 15. If there is sufficient rain falling to raise the water table, the pool water level should rise faster. A) It started out higher than the water table. And B) there is a deck around the pool that does not absorb water. Most decks are designed to allow rain water, and pool splash water to drain back into the pool.

3 If there is a waterproof vinyl liner that is fitted over the top of the reinforcing pool wall, and there is a 4" thick pool deck as stated in post 19, around the pool, how can air escape from the ground as the water table rises with the rain event?

By installing porous vertical pipes through the deck, and through the overhung pool liner if it is there, near the pool edge, there can be no build up of air pressure from the rising water table between pool liner and pool walls.

I hope I have been able to explain myself properly this time. I wish I had your skill in generating pictures. I tried to post a picture last night, it must have escaped, post and all. Thank you for your patience.

Thanks again, Bob. You have anticipated what I was going to post (ref. #39)...but first I had hoped to get some feedback from Al as to particulars that might help explain the possibility of compression of air between his pool's shell and liner. The question would always arise as to how a storm and radical rise in below-ground water surface could lead to air-induced ballooning of the pool liner...perhaps flexion of the pool's shell?

As to air pocket entrapment to the point of "inflating" a blister in the liner, my "solution" would have tended more towards check valves fitted into the liner itself near the top (near skimmer level). By this means, any upward-migrating, increasing air pressure behind the liner would be relieved. In fact, I am surprise that Al's pool is not already fitted with such a "system"...which leads me me to surmise that any air in significant amount beneath the liner might have been due to faulty liner installation (or faulty installation procedure). Of course, as I've stated, it would seem reasonable to test to determine cause before any corrective procedure; since the "defect" has been described as ballooning, not only does that suggest air...it also suggestw that (pool draining and) puncturing of the liner at the defect site (puncturing by the pool warrantor, i.e., the pool construction firm, that is) ought to prove the "air theory" if the blister recedes...and the shell is found to be unperturbed.

I can appreciate your frustration on account of my and others' "excursion" into possibilities regarding water pressure. Because Al's posts led to the impression that his new pool was more or less always within the water table [when he digs shallow "wells" they always fill rapidly], I was simply grasping for some explanation of how water pressure could (against all intuition) cause the liner "blistering" problem...whether it be due to pool placement in reclaimed swampland, either in inland N. Florida and S. Georgia or along the IC waterway along the coast.

Hmm, those pictures seem misleading a bit, if you have water rise above ground surface it would inflow into the pool and equilibrate the pressure. If water were at the ground surface outside of a pool full of water, how much water pressure are we talking about? 1 foot of head maybe, so about 62.4 psf. I believe the water pressure would be less in this case than the soil pressures under dry conditions when the pool was drained. So the pool should be able to resist this small amount of water pressure, as it would be designed to resist the soil pressures when it was drained for cleanings. The problem arises when the water table is up and the pool is drained.

But the OP states he does not drain the pool. Now what else can it be except trapped air?

RCE.

The drawing was intended merely to offer one possibility based on an overlooked but well known Florida landscape feature, namely: the intra-coastal waterway. You are correct, perhaps, in that "normal" water table level surrounding the pool might have been depicted at a too high level. My conception was of a rise in the waterway channel of perhaps as much as 10 feet (remember, we're talking hurricanes and hurricane induced ocean surges)...ten feet of additional head. Remember also that the pool might have withstood numerous instances of such overpressure incidents before it finally collapsed. Finally, remember that it is the pool's liner, not the shell, which is (now, since pool shell buttressing) being affected...which must structurally withstand any added pressure. As the picture shows, my scenario does not contemplate the (towards the house) overflowing of the inland waterway bank...to the extent that the parcel in which the pool rests is inundated. While it is true that the parcel would tend to inundate by rising water forced through the channel bulwarks (as Bob mentioned), my conception was that the rising water (especially as upwardly confined by the pool itself and by the paved pool apron) might reach a depth (and pressure) wherein the pool liner yielded before the "ground" water rose to a point at which the pool was inundated. In this scenario I do not believe it to be gas which would cause the liner problem...because gas is compressible and because it should tend to rise and bubble out at ground surface.

There is another scenario, perhaps one that will explain Al's pool problem as well, in which gas could be a significant factor. It also would explain how the the water inside the pool could itself have contributed to the pool liner failure. When competed I will post that scenario separately.

I think the thing to consider isthe near surface water table between the levee and the sidewall of the pool substantially confined. Such water tables typically are not substantially confined this shallow relative to the horizontal conductivity of the shallow aquifer. In an unconfined situation the water will seep out to the surface when the hydrostatic head reaches the surface elevation. Thus where you EGL is above the ground surface the water would seep out and flow overland. So the effective water pressure the pool wall will at most be only as high as the ground surface above the the surface of the water in the pool. If water flows overland it would rain into the pool raising the water level in the pool offsetting the pressure from the water table. Since his water level in the pool is likely about 1 foot below the ground surface, the maximum differential head achieved between water in the pool and groundwater is 1 foot, before water begins flowing overland. Now if there is a confining layer, the pressure depends on the overburden holding the confining layer down, the vertical conductivity of the confining layer and the horizontal conductivity of the aquifer. The water table will have an uplift pressure on any confining layer upgradient of the pool equal to the effective pressure on the sidewalls of the pool plus any head loss to the aquifer.

Well said.

I don,t see any mention of a levee from the OP.

I would suggest hiring a structural engineer registered and practicing in the State of Florida. The unit weight of water (pool water) is approx. 63 lbs per cubic foot. The weight of fully saturated soil/dirt is much larger (often 90 lbs. per cubic foot). Therefore, the pressure exerted from outside the pool is greater than the pressure excerted from inside the pool - all of this on the liner or wall behind the liner. If the wall is not sealed, satruated water is possibly filling up behind the liner.

If you are saying is is air behind the liner and it blows uo like a balloon with the pool full then I am at a loss why this occurs during storms.

That is exactly what I think. Dig a hole. install pipes where needed. Build walls and reinforce with concrete and rebar. Smooth it all out. Now install a vinyl liner inside that and fold it over the top of the wall and seal it there. When the water table in the area is at normal level, the bottom of the hole dug for pool was dry. With water in the pool, the weight of the water pushes any air between the liner and wall into the dirt fill material behind the wall, because the wall is not waterproof by itself. That is why they need the vinyl liner.

As the storm dumps water onto the ground, it raises the water level in the area. Any air in the dirt under the pool will be pushed up till it contacts the pool wall and liner. Air can pass through the wall, but not the vinyl liner.The air will be pushed up the sides of the vinyl liner. If the liner to wall area is not vented to atmosphere, the air has no escape from the sealed area on the top of the wall. The water level keeps rising, and the air pocket gets smaller and smaller.But the pressure is rising as the same amount of air is forced into a smaller and smaller area. Would that be enough to push that liner in?

Actually saturated mineral soil has a unit weight usuallyof about 130 pcf to 140 pcf (except diatomaceous soils which may weight 90 pcf). A dense, well-graded, gravelly sand would have a submerged unit weight of about 80 to 90 pcf. The lateral pressure from the submerged soil would be about 0.5xD_s²x125+62.4xD_gw, thus at 1 foot it is about 125 psf, and at 10 feet it would be 6874 psf. However, soil pressure does not exert on the liner, only on the wall supporting the liner, unless the liner is directly exposed to soil contact. The pressure acting on the wall is 0.5xD_s²x125+62.4xD_gw-62.4xD_w. In general, soil pressure does not transfer to the water. therefore the hydrostatic pressure applied from outside the liner is approximately the hydrostatic pressure outside the structure (also including some minor effects for bouyancy for the liner materials and head loss for seepage through the walls). The pressure holding the liner in place is the hydrostatic pressure from water in the pool and any bonding agents applied to the liner to bond it to the structure. The greatest pressure acting on the liner is 62.4xD_gw-62.4xD_w.

If I understand you correctly, you do not think the hydrostatic pressure is causing the liner to become deformed?

hi bob from joe,

i also don't think this is hydrostatic pressure. i do not have the numbers to back me up as other posters have. commen sense tells me that the air in the soil is trapped by the concrete when it rains and the water table rises. the air tries for the easiest way out.

one possible simple fix, is to go around the outside of the pool and drill vent holes thru the concrete. shove perforated plastic pipe down the holes, with some type of air vent glued or set into the top. it may not work, but the cost to try is very cheap. you can rent a concrete drill for less than $40 per day.

joe

Al,

If your still around, can you provide further detail about your new pool's liner "blistering" problem:

• Size up and down, and laterally, of blister?
• Only one or numerous liner detachments/ballooning?
• Location near pool rim or further down towards pool bottom?
• At shallow end or deep end of pool, or somewhere in between?
• Near to or at a distance from from the pool skimmers (overfill ports/flappers)?

Finally/otherwise, what has the pool installer offered as the cause of the problem...and the solution needed to correct the (what seems to be a) mfg/installer materials and/or workmanship defect?

Thanks.

CowAnon,

Thanks for all you guys interest in this serious problem. I am attaching numerous .jpg pictures I took of the pool at the worst part or the damage. Hopefully this will indicate what I am going through. This is water behind the liner, not air!! I have tried to send many more but can't get this to work well. If you will let me know what your email address is I will send all of them to you. You might be able to look at these few and see the problem all around the pool. I explained to the pool person that installs the same pool in Jacksonville and he indicated they have the same problem over there. He indicated my solution of adding a french drain on each side,with a central point at the end of the pool, where I would put in a sump pit and sump pump would be the best way to go. I could then pump the water to vegetative swales at the front of the house. You can't imagine how much rain we received when Fay came through. There are worse pictures than these.

Let me know if you would like me to send the pictures.

Yeah i would be pissed if some salesman tried to convince me there was enough water pressure seeping through the concrete walls to force a liner filled with water to float like that. In order for the liner to float it must push the water retained inside the liner out and upwards, you must have enough pressure penetrating the concrete walls to shear the adhesive bond between the liner and the walls, and lift the water inside the pool. I have seen liners in dairy wastewater ponds float like this, but it is always caused by trapped methane generated from old waste disposals prior to the installation of the liner. This looks just like that. In any case this appears to be an issue of improper installation, you should seek legal council and make the installer aware that you may be filing against their license and taking them to court, unless they repair the poor quality worksmanship.

All good points to consider, but one. Don't tip your legal hand (show your cards) in any way. The strategy at this stage is "keep records and try to give 'em enough rope to hang themselves. In other words, don't get mad...just get satisfied. Out in California these kinds of faulty problems also show up...probably everywhere else, too. It might be better not to delay too much, what with the housing situation and so many failures in housing related services and trades these day.

But Al Stanley probably already knows all that.

CA