Am I too close to the edge of my excavation?

Nofronts

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Jun 19, 2022
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Hi, I had my yard professionally excavated for my above ground pool. After setting it up yesterday I feel that I'm to close to the edge of the excavation and worry that if I put water in it will expand and go off. Can someone let me know if this is too close and what I can do to fix it before I fill it up?

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AK-

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That is a bit too close. If any soil washes away with heavy rain you risk the integrity of the wall support. I would consider building a small retaining wall to prevent any soil from washing away.
 

AK-

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Thanks for the reply, do I need a certain type of wall because it's supporting a pool?
The idea is a wall to keep the dirt currently supporting the pool in place. A wall to truly support a pool requires an engineer.

Just to confirm… is all the pool over undisturbed soil (no fills)?

BTW, it may be just the picture, but on you first picture the wall doesn’t look very level and one of the uprights seems a bit sideways.
 
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AK-

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One other comments…

On the side that is semi inground… it seems the top of the wall is too close to the ground. Are you planning to fence out the pool? The way it is it may be a code violation (and a huge liability).
 

Nofronts

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There is a little bit of fill in that area but like 90% is undisturbed.

The pool is getting a deck in July with gates for code.

Right now the pool has only like 4 inches of water in it so the wall is kinda pushing in and pulling out in places so I think that is why it looks funny.
 

AK-

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The issue with fill is it may compress differently than the undisturbed soil. Since it is fully assembled you should keep an eye on that side for the first few years.

Add about a cup of bleach each evening and mix the best you can with a broom to avoid premature algae. Also the liner should not be exposed to sunlight without being filled for too long.

On the side downhill I’d build a small (probably 2 courses) retaining wall, lay some geo-textile over the soil and fill with some river stone. That would ensure the water can properly drain thru the stone and the soil won’t wash away.
 

AK-

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One other question, my soil is clay. Is that good or bad for my situation?
Depends on what you mean by situation…

I’m no soil engineer… so talking by experience… my soil is clay and I have a similar slope… under heavy (2+ inches per hour) rain it washes away considerably. That can be mitigated by some drainage above the pool.

From the research I did when I built my “No No” pool clay has poor mechanical compression (meaning it will still have room to be compacted over time even after using a gas powered compactor).
 

Newdude

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Hey nofronts and Welcome !!!!

So, fun math for you. You didn't say but it doesn't matter for making my point. Let's assume the pool is 21ft round. It has 91k lbs of water in it. The roughly 40% that is on the built up side needs to support 36k lbs, or 6 Ford F350s on just that area.

A retaining wall would need to hold back alot more than just dirt.
 

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AK-

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Hey nofronts and Welcome !!!!

So, fun math for you. You didn't say but it doesn't matter for making my point. Let's assume the pool is 21ft round. It has 91k lbs of water in it. The roughly 40% that is on the built up side needs to support 36k lbs, or 6 Ford F350s on just that area.

A retaining wall would need to hold back alot more than just dirt.
Not necessarily. Based on the picture the slope seems to be less than 30 degrees, so the whole pressure would be absorbed by the soil. But that soil must remain in place.

But to your point something like this is possible (as long as you have an engineer)
1655690611686.jpeg
 
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Hey @Nofronts, even though I believe @Newdude ’s math is not correct I share his concern. If your pool wasn’t already fully assembled with liner and water my suggestion would have been to excavate a little more and have the whole pool on undisturbed soil. Since the pool is already with some water (and assuming you don’t want neither to buy a new liner nor to end up with wrinkles in the liner) you should methodically and frequently inspect the filled side to ensure it is not sinking. If it does sink drain down to 1ft immediately.

My guess in size is a 24ft round that would weight about 38 tons. If only 10% of it is on filled soil that still is about 4 tons of water. If that soil sinks a gap may form under the bottom railing that could either over stretch the liner or remove the railing from the wall, and in either case that is very likely to cause a wall failure. What would be the damage is over 10K gallons of water wash down hill in an instant?
 

Newdude

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My guess in size is a 24ft round that would weight about 38 tons.
Math isn't a guess. :) Radius squared X pie X 4ft water depth X 7.481 gallons per cu ft X 8.34lbs per gallon.

112,843 lbs for a 24 ft pool.

I had 91,000 for a 21ft / 4.25 ft tall to make the point.

Either way, the part that is built up is going to need to be undisturbed because 30-40% of the pool is sticking out. Many have tried and it never ended well. Well, there had to have been a few that got lucky, but it wasn't many. We don't advise building up on flat ground, much less a hill.
 

Toxophilite

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Depends on what you mean by situation…

I’m no soil engineer… so talking by experience… my soil is clay and I have a similar slope… under heavy (2+ inches per hour) rain it washes away considerably. That can be mitigated by some drainage above the pool.

From the research I did when I built my “No No” pool clay has poor mechanical compression (meaning it will still have room to be compacted over time even after using a gas powered compactor).
That's the main problem with clay. It doesn't compact, because it's dang near water solid when wet and rock solid when dry. It's not granular enough for water to pass, and you can't compress water. But, when that water dries off in the dry season, the shrinkage then happens and is substantial. The reverse is true if you build on dried out clay, it then expands substantially during the wet season. So, you have to deal with what nature gave you. Maintaining a consistent moisture level with ground covers, mulching, drainage, etc.... any ways of keeping that area prone to severe dry and wet periods from experiencing the cycles.
 
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Nofronts

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The pool is 27' round. So the more responses I get the more concerned I am with this pool set up. Am I at the point where I should be starting over? The excavator said he does these all the time in my area just like this and never had an issue.
 

AK-

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The pool is 27' round. So the more responses I get the more concerned I am with this pool set up. Am I at the point where I should be starting over? The excavator said he does these all the time in my area just like this and never had an issue.
Does the excavator contractually guarantee that?

If wasn’t for the clay filling I wouldn’t be much concerned (stone dust, that is still not recommended, would do much better).

The excavator may be right that it may be unlikely to fail. But if it does fail you are going to have 15K gallons of water hushing down hill.
 

Nofronts

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I would say 3 out of 18 are on disturbed ground. And there is nothing down hill except woods then a corn field like 200 yards back.

So with all this being said if I get a 2 course retaining wall built will that be enough to prevent the ground from pushing out there? Just not sure if I should move forward with the retaining wall or just start taking the pool down.
 

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