Can a concrete pad support AGP?

kellyfair

Gold Supporter
Bronze Supporter
Jun 29, 2016
4,147
Tampa, FL
Pool Size
7000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
I decided to do option 1 but the guys kind of messed me up a little. They leveled out the area but they dug out the grass but built it up instead of down!! Now I have to get a retaining wall in and the cheapest option is to use lumber vs cinderblocks but the lumber will last probably 10 years he says.. either way I'm not happy about that and I will negotiate the price down if possible. They are coming back in 2 days to put in the retaining wall. I'll add pictures then. Thanks everyone for your suggestions
I’m confused... if they built the area up, what is the retaining wall for? To keep weight of pool from displacing the dirt it is sitting on?

I would insist that they do what you originally asked them to do.
 

Woodstock1234

Gold Supporter
Aug 4, 2020
103
Illinois
I decided to do option 1 but the guys kind of messed me up a little. They leveled out the area but they dug out the grass but built it up instead of down!! Now I have to get a retaining wall in and the cheapest option is to use lumber vs cinderblocks but the lumber will last probably 10 years he says.. either way I'm not happy about that and I will negotiate the price down if possible. They are coming back in 2 days to put in the retaining wall. I'll add pictures then. Thanks everyone for your suggestions
Hopefully, they didn't build up the area that the pool will sit on.
 

JoeSelf

Gold Supporter
Jun 18, 2014
760
Glassboro, NJ
You need to dig down to undisturbed soil & level for the pool. If they just thru in some soil and compacted it will settle and then the pool could fail. If they used stone, it would need to be done in small lifts and compacted until the area was level.
 

cj133

Well-known member
May 6, 2018
355
NJ
If the area was built up it needs to be compacted some how. There are different methods depending on what the soil is but it needs to be done correctly or it'll settle.
 

chi-chi

Active member
Jun 21, 2019
35
DC
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
What they did is they first removed the grass and then they added what he called a crushed compacting sand/stone (I forgot what grade or exact name is) and then they compacted, added and compacted and rinsed and repeated until it was level. They added some sand I had on top and compacted again. The retaining wall is for where the high side just stops. Its and L shape that needs the retaining wall.. I will take pictures tomorrow. But I wanted to use Ground contact pressure treated lumber for them to build the wall and want to know if that is sufficient?

I'll post pictures of the area tomorrow as it is raining today. I also plan to add 4" concrete blocks in the area for the legs, level with the compacted area.
 

jseyfert3

Silver Supporter
Bronze Supporter
TFP Guide
Oct 20, 2017
1,494
Southern WI
Pool Size
15000
Surface
Vinyl
Chlorine
Liquid Chlorine
What they did is they first removed the grass and then they added what he called a crushed compacting sand/stone (I forgot what grade or exact name is) and then they compacted, added and compacted and rinsed and repeated until it was level. They added some sand I had on top and compacted again. The retaining wall is for where the high side just stops. Its and L shape that needs the retaining wall.. I will take pictures tomorrow. But I wanted to use Ground contact pressure treated lumber for them to build the wall and want to know if that is sufficient?

I'll post pictures of the area tomorrow as it is raining today. I also plan to add 4" concrete blocks in the area for the legs, level with the compacted area.
That seems to me like a reasonable way to build up a surface for a pool if compacted well, but I'm not an expert.

Ground contact pressure treated lumber is for, well, ground contact. :) So that should be fine, but yes it will not last forever.
 
  • Like
Reactions: chi-chi

phonedave

Well-known member
May 30, 2012
779
Montville NJ
Pool Size
17000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Hayward Turbo Cell (T-CELL-5)
What they did is they first removed the grass and then they added what he called a crushed compacting sand/stone (I forgot what grade or exact name is) and then they compacted, added and compacted and rinsed and repeated until it was level. They added some sand I had on top and compacted again. The retaining wall is for where the high side just stops. Its and L shape that needs the retaining wall.. I will take pictures tomorrow. But I wanted to use Ground contact pressure treated lumber for them to build the wall and want to know if that is sufficient?

I'll post pictures of the area tomorrow as it is raining today. I also plan to add 4" concrete blocks in the area for the legs, level with the compacted area.


Here is the thing. There is nothing inherently wrong with placing a pool on properly compacted fill. The issue is, how do you know you have properly compacted fill.

You cannot just "put in dirt and compact it really well" even if you are using the correct fill material, you cannot just "compact it really well". Soils have a optimal moisture content (percentage) where they will compact to their maximum dry density. If you have more or less water in the soil, you can compact it until the cows come home and it will never reach its maximum potential density. Then 2 years down the road when it dries out some, or it rains and it gets a little wetter, with your pool sitting on it, it compacts some more. No bueno.

Some soils are more forgiving than others. The goal in construction (most of the time) is to reach 95% of the maximum dry density. Some soils have a flatter curve. What that means is that if your moisture content is between say 4% and 9% you can still hit that 95% compaction. Other are really sharp, and if you are more than a 1% off you will never reach 95% compaction.

So how do you know these curves and measure the compaction? You hire a geotechnical engineer (sorry, I left that field a long time ago and no longer do site inspections). They run compaction curves (Proctor tests) in the lab and then measure the in place density in the field.

Now we come to point #2. Isn't that a lot of overkill you say? I'm building a pool, not a garage. Ahh, there is the difference. A pool is HEAVY. More psi loading than a garage. Also, a garage on a slab is much more rigid, and is able to bridge minor variations in the substrate. An ABG is a big flexible bag of water with almost no structural rigidity. If something starts to settle, the whole bag o' water is going in that direction, with disastrous results.

Which brings us to point #3. A concrete slab is only as good as the ground under it. As I said above, a slab can bridge some very minor imperfections in subgrade preparation. But chances are it will crack, and shift, and that is worse under a pool than a small amount of soil settling. To have a slab that will not crack or shift, you basically have to prepare the ground as you would for a pool anyway.
 
  • Like
Reactions: JoeSelf and chi-chi

chi-chi

Active member
Jun 21, 2019
35
DC
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
Here is the thing. There is nothing inherently wrong with placing a pool on properly compacted fill. The issue is, how do you know you have properly compacted fill.

You cannot just "put in dirt and compact it really well" even if you are using the correct fill material, you cannot just "compact it really well". Soils have a optimal moisture content (percentage) where they will compact to their maximum dry density. If you have more or less water in the soil, you can compact it until the cows come home and it will never reach its maximum potential density. Then 2 years down the road when it dries out some, or it rains and it gets a little wetter, with your pool sitting on it, it compacts some more. No bueno.

Some soils are more forgiving than others. The goal in construction (most of the time) is to reach 95% of the maximum dry density. Some soils have a flatter curve. What that means is that if your moisture content is between say 4% and 9% you can still hit that 95% compaction. Other are really sharp, and if you are more than a 1% off you will never reach 95% compaction.

So how do you know these curves and measure the compaction? You hire a geotechnical engineer (sorry, I left that field a long time ago and no longer do site inspections). They run compaction curves (Proctor tests) in the lab and then measure the in place density in the field.

Now we come to point #2. Isn't that a lot of overkill you say? I'm building a pool, not a garage. Ahh, there is the difference. A pool is HEAVY. More psi loading than a garage. Also, a garage on a slab is much more rigid, and is able to bridge minor variations in the substrate. An ABG is a big flexible bag of water with almost no structural rigidity. If something starts to settle, the whole bag o' water is going in that direction, with disastrous results.

Which brings us to point #3. A concrete slab is only as good as the ground under it. As I said above, a slab can bridge some very minor imperfections in subgrade preparation. But chances are it will crack, and shift, and that is worse under a pool than a small amount of soil settling. To have a slab that will not crack or shift, you basically have to prepare the ground as you would for a pool anyway.
I know I won't be able to get an engineer, but I am trying to get it as good as possible for my ground. I'm hoping they come back today so that they can put in the retaining wall and I can take pictures. I also bought 4" thick concrete blocks that I plan to have them put in flat at all of the leg locations like the attached images from another posters thread..
 

Attachments

  • 20190530_204147-min.jpg
    20190530_204147-min.jpg
    762.4 KB · Views: 15
  • 20190603_185642.jpg
    20190603_185642.jpg
    726.7 KB · Views: 15
  • 20190602_091130-min.jpg
    20190602_091130-min.jpg
    1 MB · Views: 14
  • 20190601_124746-min.jpg
    20190601_124746-min.jpg
    935.4 KB · Views: 14
  • 20190531_134200-min.jpg
    20190531_134200-min.jpg
    913.4 KB · Views: 13
  • B67950D8-BCA5-47FA-98C1-0158ACCF5E3B.png
    B67950D8-BCA5-47FA-98C1-0158ACCF5E3B.png
    736 KB · Views: 14
  • image.jpeg
    image.jpeg
    56.3 KB · Views: 15
Last edited:
  • Like
Reactions: kimkats

anjy99

New member
Apr 10, 2021
1
Denver, CO
We did a circular paver patio so we can have patio chairs out when it's not pool season and otherwise the pool is set up for summer
 

kellyfair

Gold Supporter
Bronze Supporter
Jun 29, 2016
4,147
Tampa, FL
Pool Size
7000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
Super neat work so far!
 

Enjoying this content?

Support TFP with a donation.

Give Support

chi-chi

Active member
Jun 21, 2019
35
DC
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
Here is an update, they're currently working on the ground leveling. They have put up a retaining wall made from Ground contact Lumber and they are putting in the 4" thick concrete pavers at each of the leg locations. Then they will add another layer of compacting material and compact it all level..
 

Attachments

  • 20210410_130614_copy_2250x3000.jpg
    20210410_130614_copy_2250x3000.jpg
    785.1 KB · Views: 17
  • 20210410_130607_copy_2250x3000.jpg
    20210410_130607_copy_2250x3000.jpg
    888.8 KB · Views: 16
  • 20210410_130552_copy_2250x3000.jpg
    20210410_130552_copy_2250x3000.jpg
    960.1 KB · Views: 17
  • 20210410_130539_copy_2250x3000.jpg
    20210410_130539_copy_2250x3000.jpg
    780 KB · Views: 17
  • 20210410_130526_copy_2250x3000.jpg
    20210410_130526_copy_2250x3000.jpg
    929.4 KB · Views: 17

chi-chi

Active member
Jun 21, 2019
35
DC
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
Okay update: the ground is prepped and ready. I am open to any more suggestions or ideas.. I plan on renting a compactor possibly to compact it one last time? Is that a good idea or should I avoid that since I might crack some of the 4" concrete blocks? Also I still plan to put 2" x 12" pressure treated lumber at each leg per the instructions despite already having the concrete blocks there. Is that a bad idea? I'd rather go overkill if it's not going to harm anything .
 

Attachments

  • 20210423_093720_copy_3000x2250.jpg
    20210423_093720_copy_3000x2250.jpg
    806 KB · Views: 13
  • 20210423_093701_copy_3000x2250.jpg
    20210423_093701_copy_3000x2250.jpg
    604.3 KB · Views: 12
  • 20210423_093619_copy_3000x2250.jpg
    20210423_093619_copy_3000x2250.jpg
    820.4 KB · Views: 11
  • 20210423_093602_copy_3000x2250.jpg
    20210423_093602_copy_3000x2250.jpg
    1,002.2 KB · Views: 13
  • 20210423_093551_copy_3000x2250.jpg
    20210423_093551_copy_3000x2250.jpg
    828.9 KB · Views: 13
  • Love
Reactions: Newdude

kellyfair

Gold Supporter
Bronze Supporter
Jun 29, 2016
4,147
Tampa, FL
Pool Size
7000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
Will the entire bottom of the leg fit on the blocks? If so, I’m not sure why you would put wood down, or even where you would put it?
 

chi-chi

Active member
Jun 21, 2019
35
DC
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
Will the entire bottom of the leg fit on the blocks? If so, I’m not sure why you would put wood down, or even where you would put it?
So I put the two concrete blocks based on a post by @sammckin and it does look like the u shaped legs fit, but the reason I am thinking to do the pressure treated lumber is because the instructions call for it and it's a softer less abrasive material. Plus I am hoping it would avoid any potential cracking to the pavers even if they're 4" thick. I plan to sit a tarp in between the concrete blocks and the lumber and another tarp over top of the lumber in between the legs and the lumber. Is this a bad idea or just overkill? I'm okay with overkill as long as it's not detrimental..
 

chi-chi

Active member
Jun 21, 2019
35
DC
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
Oh and the wood would sit right on top where the concrete blocks are. The raised height of 2" is good too because I plan to use the 4'x8' foam insulation and a waterproof flooring underlayment which will add 2" in height under the pool floor..
 

kellyfair

Gold Supporter
Bronze Supporter
Jun 29, 2016
4,147
Tampa, FL
Pool Size
7000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
Personally I think that is overkill. The 4” thick blocks are highly unlikely to crack, nor will they rot.
 
  • Like
Reactions: chi-chi

chi-chi

Active member
Jun 21, 2019
35
DC
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
I'll take heed and just use the blocks praying they don't crack.. I am considering one last compaction with the a plate compactor. I just need to find one with a rubber plate pad. Just to be sure it's solid
 

kellyfair

Gold Supporter
Bronze Supporter
Jun 29, 2016
4,147
Tampa, FL
Pool Size
7000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
If the blocks are on firm foundation, it would take a lot to crack them. Don’t worry!
 
  • Like
Reactions: chi-chi