Vinyl In-ground pool in Clay Bowl

[trylonmac]

Our 22' x 42' x 8' in-ground, free-form vinyl pool was built in an area of heavy clay. The first three feet below the ground surface are sand and gravel, with up to 13 feet of clay below that. A waterfall feature and series of low walls are built into a hill along one side of the pool that rises almost seven feet above the top level of the pool over a distance of just 20 feet or so. We have had the liner float off the steel walls at the end of each summer, and are seeking a permanent solution to the problem.

The water behind the liner does not drain out, despite being in direct contact with the soil, leading me to believe that there is a significant drainage issue extant. We had an engineer look at the situation, and he is thinking that the surface water is pushing the liner off the walls and we need to evacuate the water before the liner moves. One solution is to create a wick under the deep end of the pool, filling an area with permeable material until we hit sand under the clay, so that the water will collect there and flow to the sand below the clay accordingly; another is to put a dry well and pump at this lowest spot under the pool. Anyone have advice or previous experience as to which is most suited to our circumstance?

 

[JasonLion]

Welcome to TFP!

It depends very much on the lay of the land. If there is some area lower than the pool nearby you can put in french drains around the pool to direct water to the lower area. If the land is relatively flat or the pool area is lower than the surroundings you will need a dry well of one kind or another, either punching through the clay layer or with a sump pump.

Keep in mind that you don't need to get the ground water level down all that far. Getting the ground water to stay at least two feet below surface level should be sufficient.

 

[trylonmac]

Welcome to TFP!

It depends very much on the lay of the land. If there is some area lower than the pool nearby you can put in french drains around the pool to direct water to the lower area. If the land is relatively flat or the pool area is lower than the surroundings you will need a dry well of one kind or another, either punching through the clay layer or with a sump pump.

Keep in mind that you don't need to get the ground water level down all that far. Getting the ground water to stay at least two feet below surface level should be sufficient.

Thanks for the response; is there any concern that moving too much surface water from around the pool might desiccate the clay bowl and cause a problem?

 

[JasonLion]

If the ground isn't actively squishy that shouldn't be an issue. They must have gotten the water table down when they put in the pool. Most likely it goes down naturally at certain times of year, so this won't be any different from that.

 

[trylonmac]

If the ground isn't actively squishy that shouldn't be an issue. They must have gotten the water table down when they put in the pool. Most likely it goes down naturally at certain times of year, so this won't be any different from that.

I don't know that the water table is at issue, we are on a hilltop elevation of 70 feet; I think it is just surface water collecting around the pool after strong rains with nowhere to go that is causing havoc. We have a 1000 square foot patio, built of pavers on sand, abutting the pool opposite the water feature/hill; it seems as if that area could collect quite a bit of surface water. The ground is not squishy now, although it was before the pool went in in some areas (we took that to be puddling at the bottom of a hill with a 25 degree slope). I think I prefer the wick approach, over the sump/pump; seems to be a bit more resistant to problems, you agree?

 

[JasonLion]

Indeed, my terminology is wrong, but the idea is the same. The water isn't always there, so removing it shouldn't pose any problems.

Yes, a wick, as you call it, would be the simplest solution. As long as there is somewhere for the water to go that is reasonable accessible, a drainage pipe can be installed so that the water will flow there.

 

[rcy]

When you talk about a french drain, are you meaning the round tube with the perforated holes in it (sometimes called weeping tile where I live, although they don't use tile anymore). Where is live there is about 2" of topsoil, then very heavy red clay. The pool builder installed that tubing around the entire pool and dug a sump well (about 5 or 6 feet deep, maybe) that the tube leads to. I was told to be very adamant about checking the level in the sump well, especially in the winter when the pool level is lower (due to draining to blow the pipes for winter). The builder told me in an area with sandy or normal soil, they wouldn't install the sump well.

In your case, it may be too late (or involve way too much work) to do something like this.

In the pic below you can see the black tubing around the bottom of the pool wall, and in the top right corner you can see the big black vertical tube that became the sump well (after it was cut to ground level when the pool was done).