Leveling ground for above ground pool

[Indept]

I just joined, this looks like a great site. I looked but did not see a search function so here's my question:
I am replacing my 24' round above ground pool with an 18 x 33' above ground pool. The new pool will basically sit where my existing one is with, of course, an extra 9' of ground space needed. My yard is slightly sloped and I know the best way is to bring the high point down to the lowest to assure well packed earth. The drop off is only about 6". I am not having it installed until next May so IF I raise the lower portion with new soil now (I plan to go a few extra feet past where the new pool will sit) and I am going to install a retaining "wall" to assure it stays, will the new dirt settle enough over the winter with rain, snow etc. (I live in NJ just east of Philadelphia, Pa)?. I am not going to tear down the old pool until next spring to help keep it from erroding and I will have an installer come out & level it with a Bobcat front end loader and pack it down with that hopefully. I don't want to have to remove 6" of soil to bring the existing pool base down if I don't have to. I would have to have it removed if I did (it's a mixture of soil & clay so it's not really usable anywhere else in the yard). Also I have a deck that is just above the existing pool height so if the new pool is installed 6" lower, I will have a lot of extra work to do to mate the deck with the new pool.

Thanks for any advice.

 

[linen]

Welcome to tfp, Indept

If you are going to add fill, make sure it is compacted well (and is fill that compacts and holds). Your idea of putting it there this fall is a good one imo. I would also use a plate compator on it this fall. Then really compact it well again next spring with the heavy equipment and compactor. Add extra fill so once compacted (X2) you will still have a high enough base.

There is risk with this approach, but if done correctly, it can work.

 

[cramar]

Dittos, it has to be done properly or you risk pool failure.

 

[phonedave]

Use structural fill - not "free fill"

You need a well graded fill with no organics in it. Well graded means it has an equal amount of all grain sizes in it. No organics means nothing that will rot and compact - no topsoil, no leaves, no tree roots, no trash. You also do not want large chunks of rock in it, such as broken concrete.

How much fill are you looking at? For my money I would use what is called QP in your area (most likely, I live near you sort of), which is short for Quarry Process. It may also be called DGA/Dense Graded Aggregate, Crusher Run, or a bunch of other local terms - unfortunately people come up with a bunch of different names for the same thing. It is a mix consisting of 3/4" stone down to stone dust. It is very forgiving to work with as far as compaction is concerned. IT is also not expensive. It is however heavy and a pain in the rear to shovel.

It sounds like you are going to fill 6". For me, I would have at most a 30 degree side slope on that fill. Since is is so short, I would even go out to more like 20 degrees, unless you are adding some sort of reinforced wall.

Place the material in 3" lifts, compacting each one well with a vibratory plate compactor - the heavier the better.

Oh, and the search function is on the top right, just above the "Pool School" button.

-dave

 

[Indept]

Thanks for the replies.

phonedave,
You wrote:

You need a well graded fill with no organics in it. Well graded means it has an equal amount of all grain sizes in it. No organics means nothing that will rot and compact - no topsoil, no leaves, no tree roots, no trash. You also do not want large chunks of rock in it, such as broken concrete

So even though the rest of the base (under the existing pool) is topsoil & clay, increasing with topsoil wouldn't be good enough? My concern is that I am having an installer do all the work and they will come out & level it next spring, will the fill you mentioned grade well along with the existing surface?
I was going to put a reinforced retaining wall up & fill it higher than the rest so it would not go too low when compacting, then the installer can remove the extra to bring it down to the existing pool base level?

Where do you get the QP material you mentioned?
Also, isn't it bad to have stone (3/4" you mentioned) under a pool, doesn't it tend to "resurface" under the liner once installed?

 

[phonedave]

Thanks for the replies.

phonedave,
You wrote:

You need a well graded fill with no organics in it. Well graded means it has an equal amount of all grain sizes in it. No organics means nothing that will rot and compact - no topsoil, no leaves, no tree roots, no trash. You also do not want large chunks of rock in it, such as broken concrete

So even though the rest of the base (under the existing pool) is topsoil & clay, increasing with topsoil wouldn't be good enough? My concern is that I am having an installer do all the work and they will come out & level it next spring, will the fill you mentioned grade well along with the existing surface?
I was going to put a reinforced retaining wall up & fill it higher than the rest so it would not go too low when compacting, then the installer can remove the extra to bring it down to the existing pool base level?

Where do you get the QP material you mentioned?
Also, isn't it bad to have stone (3/4" you mentioned) under a pool, doesn't it tend to "resurface" under the liner once installed?

A pool should not be set on topsoil, even if it is existing and level. A pool base should ideally be dug down to undisturbed soil, compacted, and then a sand or fines or screening layer placed, that layer leveled and compacted and then the pool set on that.

You would not set the pool directly on the QP. You would use the QP to build up the level, and then place a layer of sand or rock screenings over the entire pool footprint, compact it, and go from there.

Any of these matierals (stone, QP, sand, screenings, etc) will be available from a stone supply place. Most have a minimum deliver amount.

-dave

 

[MikeInNH]

I cannot answer your questions but I'd like to mention that 18'x33' is a great size to have. Badminton in the pool is fun. I'm curious on how you can use the same deck on a different radius pool. Good luck with the pool install.

 

[Mapoolguy]

Use structural fill - not "free fill"

You need a well graded fill with no organics in it. Well graded means it has an equal amount of all grain sizes in it. No organics means nothing that will rot and compact - no topsoil, no leaves, no tree roots, no trash. You also do not want large chunks of rock in it, such as broken concrete.

How much fill are you looking at? For my money I would use what is called QP in your area (most likely, I live near you sort of), which is short for Quarry Process. It may also be called DGA/Dense Graded Aggregate, Crusher Run, or a bunch of other local terms - unfortunately people come up with a bunch of different names for the same thing. It is a mix consisting of 3/4" stone down to stone dust. It is very forgiving to work with as far as compaction is concerned. IT is also not expensive. It is however heavy and a pain in the rear to shovel.

It sounds like you are going to fill 6". For me, I would have at most a 30 degree side slope on that fill. Since is is so short, I would even go out to more like 20 degrees, unless you are adding some sort of reinforced wall.

Place the material in 3" lifts, compacting each one well with a vibratory plate compactor - the heavier the better.

Oh, and the search function is on the top right, just above the "Pool School" button.

-dave

 

[Indept]

A pool should not be set on topsoil, even if it is existing and level. A pool base should ideally be dug down to undisturbed soil, compacted, and then a sand or fines or screening layer placed, that layer leveled and compacted and then the pool set on that.

You would not set the pool directly on the QP. You would use the QP to build up the level, and then place a layer of sand or rock screenings over the entire pool footprint, compact it, and go from there.

Any of these matierals (stone, QP, sand, screenings, etc) will be available from a stone supply place. Most have a minimum deliver amount.

-dave

dave,
What I don't understand is that you say "not to be set on topsoil"
Now I'll assume you mean not on the top undisturbed soil? Topsoil can go down for a foot or more so I don't think you mean to go down to clay. My existing pool was installed on soil that had been regraded about a year and a half before when the house was built. The installer used a bobcat to dig out the high side & redistribute that to build up the low side. a week later they put up the pool (24' round, 52" deep). It was topsoil & some clay he redistributed. It is level to within a half inch and has not moved in 12 years. The reason I'm replacing it is the lower 6 - 8 inches where I had backfilled with 3/4 round stone is rusting through all the way around (35 year warranty pool no less). The only compacting of the built up side was done with the weight of the bobcat running over it. I'm not implying you're wrong, I'm just trying to understand what really needs to be done. I watched them do that install & they dug in some patio blocks level with the surface to set the uprights on put up the frame & walls and before the closed the wall, they brought in the sand in wheelbarrow to place under the liner but nothing else under the frame.

 

[DBfan187]

That's how its done here too!

 

[Indept]

That's how its done here too!

What I described or what dave wrote?
Your description says "in the industry", do you install?

 

[phonedave]

A pool should not be set on topsoil, even if it is existing and level. A pool base should ideally be dug down to undisturbed soil, compacted, and then a sand or fines or screening layer placed, that layer leveled and compacted and then the pool set on that.

You would not set the pool directly on the QP. You would use the QP to build up the level, and then place a layer of sand or rock screenings over the entire pool footprint, compact it, and go from there.

Any of these matierals (stone, QP, sand, screenings, etc) will be available from a stone supply place. Most have a minimum deliver amount.

-dave

dave,
What I don't understand is that you say "not to be set on topsoil"
Now I'll assume you mean not on the top undisturbed soil? Topsoil can go down for a foot or more so I don't think you mean to go down to clay. My existing pool was installed on soil that had been regraded about a year and a half before when the house was built. The installer used a bobcat to dig out the high side & redistribute that to build up the low side. a week later they put up the pool (24' round, 52" deep). It was topsoil & some clay he redistributed. It is level to within a half inch and has not moved in 12 years. The reason I'm replacing it is the lower 6 - 8 inches where I had backfilled with 3/4 round stone is rusting through all the way around (35 year warranty pool no less). The only compacting of the built up side was done with the weight of the bobcat running over it. I'm not implying you're wrong, I'm just trying to understand what really needs to be done. I watched them do that install & they dug in some patio blocks level with the surface to set the uprights on put up the frame & walls and before the closed the wall, they brought in the sand in wheelbarrow to place under the liner but nothing else under the frame.

Will what your last pool installer did work - sure, sometimes. Is it "right" - no. Driving around with a skid steer is not how to compact fill. Using "topsoil" with organic material in it ias structural fill is also wrong. Now I am going to contradict myself here in the same sentence. A pool is not a light object - 40+ tons is a lot of weight, but by the same token, a pool is much smaller than what I am used to working with. Cutting a filling a 12" slope is cake. I have supervised the setting of municipal libraries on 16 feet of fill (and survived a subsiquent legal snafu because my records were correct, and the fill that I rejected was used elsewhere after I was switched to a different project).

So, to get back to pools. IS what you proposing going to work - most likely yes, but it may fail. It can settle. And remember an ABG is a system that is in balance. 80 tons of water pushing on walls that only really have tensile strenght. Thier resistence or eccentric buckling is quite low. That is why a pool needs to be level. For my money, and peice of mind (and for such a small project as a pool) I would cut to undisturbed ground,and fill where necessary with a solid fill (QP is very easy to work with, the range that it's moisture content can be in is quite large, but any good fill will work) that is compacted correctly (with anything a homeowner has access to, no more than a 6" lift - 4" would be better)

Again, this is me, I tend to overbuild things. I am sure there are plenty of pools out there that were set on wet expansive clay, wood chips, and whatever else you can find. Heck, mine is not on patio blocks, but on pieces of flagstone (and it bugs me every time I think of it - the previous owner did it that way). I am sure many of these installs do just fine, but I am also sure, of the pools that fail, all of them were installed in some questionable way.


-dave

 

[Mapoolguy]

I am an Installer in Ma. When ever we install a pool we always place pool on a level surface, Of course right But more importantly and I think this gets to your question. If you have a grading issue its always best to dig down the high end to get leveled. When as in your situation you need to build up to match installation requirement as set forth by a customer we can build up an area. We do this by bringing in a 50/50 mixture of 3/4 inch stone and stone dust. We compact this with either rental compactor or simply using bobcat machine. If you let this set for a period of time it will turn into a very solid base in which to build on.

If you use regular soil your asking for trouble down the road. If all you need is an inch or two no problem, but 6 inches and higher you want 3/4 stone and stone dust mixture. Make sure once patio blocks are leveled that you bring the rest of the area up to meet the entire track as this will create the best stability you can possibly get.

hope that helps,
Dave from
Dave's Above Ground Pools

 

[phonedave]

I am an Installer in Ma. When ever we install a pool we always place pool on a level surface, Of course right But more importantly and I think this gets to your question. If you have a grading issue its always best to dig down the high end to get leveled. When as in your situation you need to build up to match installation requirement as set forth by a customer we can build up an area. We do this by bringing in a 50/50 mixture of 3/4 inch stone and stone dust. We compact this with either rental compactor or simply using bobcat machine. If you let this set for a period of time it will turn into a very solid base in which to build on.

If you use regular soil your asking for trouble down the road. If all you need is an inch or two no problem, but 6 inches and higher you want 3/4 stone and stone dust mixture. Make sure once patio blocks are leveled that you bring the rest of the area up to meet the entire track as this will create the best stability you can possibly get.

hope that helps,
Dave from
Dave's Above Ground Pools

For the record "50/50 mix of 3/4" and stone dust" is also QP, quarry process, crusher run, or whatever else you want to call it. It is amazing how names vary from place to place. Try asking for bluestone at a supply place, then drive 50 miles away and ask for bluestone. You may get two entirely different things.

Other than that, Dave's advice above is the same as mine (except maybe compacting using the bobcat - me, I wouldn't do that)

-dave

 

[Mapoolguy]

Track machine Bobcat, sorry for not detailing this.

 

[Indept]

phonedave,

Thanks again for the reply, same to you Mapoolguy.

I don't doubt your process, I just want to find out if what they did before was correct. I intend to get the QP (or whatever they call it around here), my concern is will it compact (or should I say retain its density) the same as the surface under my existing pool which consists of soil & clay? I suspect the surface there is pretty solid since it's been there for 12+ years. I know I have to extend the fill a few feet past where the pool will sit. I intend to go about 4 feet past the end of the pool with backfill and construct a retaining wall would 2 feet past be sufficient for Qp with the rest up to the retaining wall filled with topsoil so I can landscape once the pool is in?
Also, once in place and compacted, do you forsee any issues installing the new pool on it next May?

 

[phonedave]

Track machine Bobcat, sorry for not detailing this.

It has nothing to do with tracks or wheels. It is the lack of vibration. I have had contractors try and track in structural fill with a D8 and convince me it was fine. You dig a test pit afterwards and guess what you find - voids. There is a reason even steel drum rollers vibrate. Now we are talking granular soils. A sheepsfoot roller on clayey soils is a different issue,

-dave

 

[phonedave]

phonedave,

Thanks again for the reply, same to you Mapoolguy.

I don't doubt your process, I just want to find out if what they did before was correct. I intend to get the QP (or whatever they call it around here), my concern is will it compact (or should I say retain its density) the same as the surface under my existing pool which consists of soil & clay? I suspect the surface there is pretty solid since it's been there for 12+ years. I know I have to extend the fill a few feet past where the pool will sit. I intend to go about 4 feet past the end of the pool with backfill and construct a retaining wall would 2 feet past be sufficient for Qp with the rest up to the retaining wall filled with topsoil so I can landscape once the pool is in?
Also, once in place and compacted, do you forsee any issues installing the new pool on it next May?

QP is very forgiving. Without getting into the nitty gritty of it, soils will compact the most at a specific moisture content (each soil is different). More or less water than that specific point, and you cannot compact them to their maximum density. QP is very forgiving in that it's range of acceptable moisture content is quite large. That means that unless it is soaking wet or bone dry you are going to get to very close to its' maximum density. That means it will not settle further over time. Once you get it level with the existing soil you will be fine. It will "retain it's density" asyou say.You can slope the QP up to the edge where the pool will be. a 30 degree angle should be just fine. Then cover that slope with topsoil for planting.

-dave

 

[Mapoolguy]

Not arguing man, He would be fine do let it sit over the winter and it would be fine.

 

[phonedave]

Not arguing man, He would be fine do let it sit over the winter and it would be fine.

Not arguing either.

For what he is doing (6" of fill with a pool on top) unless his natural soil is some sort of expansive clay, he should be just fine getting the site prepped and letting it sit over winter.

-dave