Question about preparing ground for my pool

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Dcarrill

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Jun 20, 2012
7
The place I want to put my pool had lots of trees and brush on it so I rented an excavator and went to town tearing it all out. I pulled up huge roots and basically ended up turning all the soil in the process. I want to place a 16' round summer escapes metal frame pool and from what I have read you do not want to backfill the dirt because it hasn't settled yet and can cause your level pool to tip over time. So my question is should I be concerned and what can I do to prevent this?

I am thinking I will dig down maybe 5" then tamp the soil down. Then buy a bunch of sand to fill in that space and tamp that as well. Is that going to be good enough or I am doomed?


Thanks in advance for any advice.
 
That's the thread that actually started making me question what to do. I assume the reason they suggest not backfilling is because undisturbed ground is compacted naturally. However the ground I plan on setting this pool on has been turned over and is not at all compacted. I'm just not sure if tamping is enough.
 
It all depends on what kind of dirt it is, and what kind of equipment you have available to compact it with.

If it is the softer topsoil then it is going to be this side of impossible to get it compacted enough to work.

Since you have the excavator there, go ahead and shave the loose/turned soil out as best you can without digging anymore undisturbed ground, then backfill to level with the screenings.
 
It is soft topsoil and unfortunately I don't have the excavator anymore. I just rented it for a day to clear up the lot and level it out. That was before deciding to get a pool and reading here. I was planning on just hand tamping it but I could rent a compactor if that would be best. I am going to have to dig it out by hand. How deep would you suggest I dig? Also you suggest screenings instead of sand?


Thanks!
 
Dcarrill said:
That's the thread that actually started making me question what to do. I assume the reason they suggest not backfilling is because undisturbed ground is compacted naturally. However the ground I plan on setting this pool on has been turned over and is not at all compacted. I'm just not sure if tamping is enough.
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Going to get a little technical here, but this is what I went to school for and did for a number of years (not pool installation, Civil Engineering - specifically earthworks)

Every soil has its own particular maximum density. That maximum density can only be acheived at a specific water content. Too much or too little water and you will never compact that soil to its maximum density. What then happens is, if the water content changes to closer to optimum, either from drying or from rain/groundwater, the soil may further compact on its own.

Some soils have very sharp compaction curves. If you stray a little bit from the perfect amount of water you are only going to get maybe 80% compaction. Other soils are more forgiving, their curves are flatter. You have more leeway and can still be within the %95 of maximum density that we look for.

As the other thread suggests, QP, Crusher Run, Quarry Process, 3/4 + fines, or whatever you want to call it (it varies from locale to locale) is a very forgiving medium. It is 3/4" crushed stone, fines, and stone dust. If compacted correctly, it will set up almost like concrete. It's compaction curve is very flat. You can vary by a couple of percentage points and still be fine.

You can recompact excavated soil, but to do it right you would have to compute compaction curves for it. It's not rocket science but you do need some equipment that really serves no other purpose and is not exactly cheap.

Your best bet to excavate down to virgin udisturbed soil, and then backfill with QP first and then sand or stone dust as a top layer (QP can be a bear to screed and get level)

You want to compact the backfill in lifts. If you are using a jumping jack type compactor, no more than 6" lifts (and really, the jumping jacks are useless unless you are in a trench). A vibratory plate compactor is better. The heavier you can handle, the better. Keep your lifts small - 8" or so, and compact them well.

Topsoil is not used for structural fill, as it contains a lare amount of organic material. Organic material rots, leaves voids, and voids collapse.

If you have large rocks you are burying, you also do not want to nest them. Spread them out and make sure there are no voids around them. Fill will eventualy infiltrate into voids.

-dave
 
Dcarrill said:
It is soft topsoil and unfortunately I don't have the excavator anymore. I just rented it for a day to clear up the lot and level it out. That was before deciding to get a pool and reading here. I was planning on just hand tamping it but I could rent a compactor if that would be best. I am going to have to dig it out by hand. How deep would you suggest I dig? Also you suggest screenings instead of sand?


Thanks!
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You don't have to "dig" any deeper than you already have, just "shave/scoop" out the loose dirt so you expose the undisturbed ground under it.

Yes, I suggest screenings over sand, first sand doesn't really compact all that well, and if it gets saturated with water then it basically becomes fluid like.

Screenings are cheaper than sand, and almost every quarry has them, it is considered a "waste" product of the screening/sifting process they use to seperate the different sizes of rock, once they get down below 1/2 inch all that is left are the very small rocks and dust, and those small rocks are usually more rounded with few if any sharp corners or edges like some rocks have.

They sell the screenings "cheap" because it is better to get something for it rather than just shove it to the side and get nothing for it, plus they aren't paying anything extra to make it, it is just a by-product of the main process.

Like Dave said this stuff will compact and once it gets wet and is compacted it basically sets up like concrete, HOWEVER, if you do not put a border all the way around it, in a heavy rain with lots of runningwater across it, then it WILL wash out like sand, just not as easy, a border all the way around and it stays put and makes for a very solid base.

Layer it in, no more than 6" deep per layer, wet it really good, allow it to sit until the surface is dry enough that it will not stick to the vibrating compactor and then run the compactor over it a couple of times, then add another layer and repeat until you get to the level you need.

Once you get to the grade level you want, use the swinging 2x6 trick to check for level, if you need to lower a high spot just use a rake to loosen the screenings and then you can move some out of your way.

Hope this helps.
 
Use this:

#10 Limestone screenings 1/10" max. in size material. It is referred to as diamond dust or crusher dust. It is used for baseball diamonds, infields and is most commonly used by landscapers as a base material for brick pavers.
*Note: We sell this as a substitute for “Slag Sand”

You can fill very deep with this stuff and it will compact very well and be very solid, and it will be cheaper as stated above.

This is the stuff I was referring to.

Trust me 16 tons of this stuff goes a LONGGGGGGGGGG way.
 
Dcarrill said:
Fantastic information Dave thank you very much. I think I may have to dig down a couple feet to get closest to undisturbed ground. Assuming I do that can you take a look at this selection and tell me what you think I should put in to fill it back up?

http://www.alstrucking.com/sand_gravel_delivery.htm

Maybe 1 foot of crushed concrete then 1 foot of mason sand?
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How much earth did you disturb if you have to go down a couple of feet? Wow

21AA limestone or the 21AA crush concrete should be fine. You don't even want to go with a foot of sand. 6" is fine.You could even use the diamond dust they sell.

As Samantha said, you want to wet the DGA before compacting it. Her method is OK. In reality, you are putting a pool on it, which is an evenly distributed load. If you get any settling, it is not going to be differential settling, as you would get with a building. Just make sure you compact the whole area. Fill in lifts, and compact each lift well (go over it more than once with the plate compactor)

-dave
 

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2 foot might be a bit of an overstatement I guess I won't really know until I get in there and start moving the soil around. Thank you both for your help I think I will start with removing the loose soil and see where I am at. At least now I have a solid game plan and feel a lot better about the whole process. :-D
 
Dcarrill said:
2 foot might be a bit of an overstatement I guess I won't really know until I get in there and start moving the soil around. Thank you both for your help I think I will start with removing the loose soil and see where I am at. At least now I have a solid game plan and feel a lot better about the whole process. :-D
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The area where you have already worked does not have to be perfectly flat and level, if you can remove the loose soil and just shave off a few high spots here and there so your fill is going to be 6" or so deep at min, then you can fill any low spots and bring everything up to level.

As long as the fill is going over undistrubed ground it doesn't matter if one spot is a foot deep and the next spot is only 6" deep.

The more level the better, but there is no need to brake your back and butt hand digging everything down to one level.
 
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