New AGP build. Looking for Feedback.

[Jometzg]

Hello all,

First time pool owner here. The wife and I decided in late June that we wanted a pool. It's been quite a ride and learning experience since then. I have browsed this site routinely since then, reading many old posts. We originally purchased a 24ft pool, but after consulting the town they wouldn't issue a permit for the work. We ended up dropping down to 21ft. At first we were going to use the installers from the pool retailer, but with with the way the yard slopes we decided to go in another direction. We hired an excavator and cut out some of the high side to fill the low side after he installed a retaining wall. He added the dirt in small lifts and compacted each lift with his mini excavator. There is pipe behind the wall that will assist with drainage.

The blocks are about 80 pounds each and geogrid has been laid between the second and third course. We are planning to let the site sit all winter before installing the pool. Is this recommended or should we go ahead and install the pool? Is there anything else we can do to prevent shifting?

Thanks

 

[doogiegh]

I believe the dirt you added will definitely compact down more. It would be best to let it sit and wait until next spring to build the pool.

 

[Casey]

You should be good to go in the spring to install the pool.

 

[phonedave]

When you say " He added the dirt in small lifts and compacted each lift with his mini excavator" you mean he placed some dirt, and then drove around on it?

Tracking in fill (as we called it in the NE when I did this kind of work) is fine for grass areas, but for structural situations - no go.

Here is the thing about fill, it reaches a maximum compaction at a specific water content. If you are above or below that water content, you can pack that fill with the biggest vibratory drum roller you can find and it will not compact to maximum density

If it sits all winter, and it is wetter than the optimal moisture content, it will not pack down. Then you put a pool on it, and it dries over the summer and it drops an inch - who knows.

I also know almost nothing about your wall. What kind of foundation was it placed on? Virgin earth, compacted 3/4 clean (as most wall systems call for) or concrete. Are there any verts in the wall? What does the wall manufacturer rate it for?

A pool is very heavy, and has no bottom rigidity. It is a big, heavy, bag of water sitting on your ground.

This is not the time for "it looks good to me" analysis

-dave


Some soils are more forgiving than others. being off a few percentage points either way on the moisture content only impacts the maximum dry density by a point or two. Other soils are much less forgiving.

 

[Jometzg]

The soil is almost a clay consistency. I can take a picture of 2 foot tall lip on the high side. The day he started excavating it was raining slightly. He had originally told me that he would need me out there with a hose, but the rain did the trick. Half the pool pad is virgin dirt since he did cut to fill. There should be about 2 foot left between the pool and the wall block.

I'm not sure what the blocks are rated for. I told him the pool could be several dozen tons in weight. He dug down and used 3/4 as the wall base and filled the hollow spots in the block with the same material. Like I mentioned, he placed Geo grid between the last two courses and added a topper (not pictured).

 

[ksguy]

Here's my experience building on a built-up site. My pool was originally built in 2000. They cut into a slope to build it, but ended up actually slightly below grade all the way around, resulting in the trough holding water and rusting the track. When I rebuilt the pool this year, I wanted it raised up to promote drainage. My site is now entirely built on compacted ground.

I started out with a dirt base that was a nasty sticky mix of damp clay due to being slightly dished out. I turned that into soil cement by tilling in about 300 pounds of portland cement into the top 4" of ground then going over it with a jumping jack wacker packer. I let that sit for a few days, then laid down a base of AB3 gravel about 1-3" thick to get the site relatively flat and then compacted several times with a plate compactor. From there I built up using gravel screenings. I went in 1-2" lifts and went over it with a plate compactor twice after each lift. When I was done, some areas were built up as much as 8". It's basically like concrete. I made sure to make my site large enough that if you go down at a 45 degree angle from the track, it stays in compacted base all the way to virgin ground. In total I put down 14 tons of gravel for a 16x32 pool.

I'm saying this just to say that raising the pool area is not trivial. Compacting a site is no joke. Those mini excavators are heavy but they put generally less than 5 psi on the soil, which is not much at all. Consider that a 200 pound person is putting around 3.5 psi on the ground and see that it's really not compacting it much more than you would just walking on it. Heck the heel of a high heel shoe can put 800+ psi on the ground. A sheepsfoot roller as used in construction to compact dirt road base to 95%+ proctor is putting down 300+ psi. The best bet for a soil site like for your pool would be using a jumping jack compactor, even if you let it sit for the winter. Personally I'd go over it once or twice this year because you're almost certainly going to have to add more soil and compact that additional soil as well. It'd be frustrating to wait until spring, then end up having to add soil and compact, just delaying your project when you're already getting antsy for a pool.

One other thing is you need to plan the site so that your pool is no closer to the inside edge of the retaining wall than the tallest part of the wall is tall. For instance if the highest part of the wall is 25" tall, the bottom track of your pool should be no closer than 25" to the back of the retaining wall blocks. I'd give it a buffer beyond that just to be safe.

Best of luck.

 

[Jometzg]

Thanks for the advice, it's appreciated. I can definitely rent a compactor for a day and go over it. I'll wait a few more weeks and do that. As for the second piece of advice, that may present a problem. The pad is semi oval in shape. For about 60% of the pad area, the pool will be as far away as the highest spot of the wall. However it tapers in to as close as 12 inches. Maybe I'll dig out the wall on the high side some more for an extra buffer. Not sure I'll get it to the total height of the wall.

 

[phonedave]

Here's my experience building on a built-up site. My pool was originally built in 2000. They cut into a slope to build it, but ended up actually slightly below grade all the way around, resulting in the trough holding water and rusting the track. When I rebuilt the pool this year, I wanted it raised up to promote drainage. My site is now entirely built on compacted ground.

I started out with a dirt base that was a nasty sticky mix of damp clay due to being slightly dished out. I turned that into soil cement by tilling in about 300 pounds of portland cement into the top 4" of ground then going over it with a jumping jack wacker packer. I let that sit for a few days, then laid down a base of AB3 gravel about 1-3" thick to get the site relatively flat and then compacted several times with a plate compactor. From there I built up using gravel screenings. I went in 1-2" lifts and went over it with a plate compactor twice after each lift. When I was done, some areas were built up as much as 8". It's basically like concrete. I made sure to make my site large enough that if you go down at a 45 degree angle from the track, it stays in compacted base all the way to virgin ground. In total I put down 14 tons of gravel for a 16x32 pool.

I'm saying this just to say that raising the pool area is not trivial. Compacting a site is no joke. Those mini excavators are heavy but they put generally less than 5 psi on the soil, which is not much at all. Consider that a 200 pound person is putting around 3.5 psi on the ground and see that it's really not compacting it much more than you would just walking on it. Heck the heel of a high heel shoe can put 800+ psi on the ground. A sheepsfoot roller as used in construction to compact dirt road base to 95%+ proctor is putting down 300+ psi. The best bet for a soil site like for your pool would be using a jumping jack compactor, even if you let it sit for the winter. Personally I'd go over it once or twice this year because you're almost certainly going to have to add more soil and compact that additional soil as well. It'd be frustrating to wait until spring, then end up having to add soil and compact, just delaying your project when you're already getting antsy for a pool.

One other thing is you need to plan the site so that your pool is no closer to the inside edge of the retaining wall than the tallest part of the wall is tall. For instance if the highest part of the wall is 25" tall, the bottom track of your pool should be no closer than 25" to the back of the retaining wall blocks. I'd give it a buffer beyond that just to be safe.

Best of luck.

Nice build. Also nice to see someone else who appears to have a background in earthworks (Proctor test gave it away).

You are dead on about the ground pressure of tracked machines. In fact, most manufactures of tracked mini devices (loaders, excavators, etc) brag about how LITTLE pressure their machines generate. It saves the homeowners lawns, but it makes them useless for compaction.

 

[ksguy]

Nice build. Also nice to see someone else who appears to have a background in earthworks (Proctor test gave it away).

You are dead on about the ground pressure of tracked machines. In fact, most manufactures of tracked mini devices (loaders, excavators, etc) brag about how LITTLE pressure their machines generate. It saves the homeowners lawns, but it makes them useless for compaction.

Funny you say that, I actually don't have a background in earthworks. I spent all last winter and spring reading everything I could so I wouldn't screw up my build. I knew I wanted to raise it and that I didn't want it to fail. Even after all the reading I was nervous going into it. Overall I'm really pleased with the way things turned out, and I think my experience was enough that I'm qualified to at least chime in on the matter. I've got a few pics of the site with most of the work done pre-pool if you want to see 'em.

Thanks for the advice, it's appreciated. I can definitely rent a compactor for a day and go over it. I'll wait a few more weeks and do that. As for the second piece of advice, that may present a problem. The pad is semi oval in shape. For about 60% of the pad area, the pool will be as far away as the highest spot of the wall. However it tapers in to as close as 12 inches. Maybe I'll dig out the wall on the high side some more for an extra buffer. Not sure I'll get it to the total height of the wall.

With the geogrid in there, you might be okay but if you're able to dig farther into the high side it would be a good thing - more pool on virgin soil.

 

[Jometzg]

Again, thanks for the feedback. I'm going to rent a jumping jack for a day and go to work. It seems like a good way to spend $80

I'll take some pictures of how things look, as it's been raining for the past 2 days.

I'd love to see pictures of your build ksguy.

 

[ksguy]

The first couple pictures aren't great, I was taking them for another purpose but they do show part of the progress.

First pic includes the outside ring which is soil cement underneath, and at the time of the picture had an inch or two of AB3 base compacted onto it. The grayish looking area between the white gravel and the more sandy looking ground is part of the soil cement.

Second pic was taken of the second load of gravel I had delivered, but you can see more of the outside "track". At the right you can see part of a pressure pad installed, it's on top of 2" AB3 and probably 3-4" of screenings. Perspective is screwy and it's hard to tell, but the area in front of the gravel is about 3" lower than the rebar. Side note, about a foot inside the rebar (towards camera) is the highest point of the site, and it ended up under about 1.5" of gravel.

Last pic I've finished spreading the 5 ton load, site is in great shape but I still needed more gravel. I had another 3 tons delivered the next day. That pic you can better see that the far end drops off. The near side is still about 1" low as well. It took about another ton of gravel to get everything where it needed to be.

 

[Jometzg]

Thanks for the pictures. Did you use both a jumping jack and a plate compactor? Should I use one vs the other?

Thanks

 

[ksguy]

Jumping jack on the bare soil, plate compactor on the gravel. The soil has to be rammed into place, whereas the gravel has to have the vibration factor as well to get the particles aligned and locked together.

 

[phonedave]

Funny you say that, I actually don't have a background in earthworks. I spent all last winter and spring reading everything I could so I wouldn't screw up my build. I knew I wanted to raise it and that I didn't want it to fail. Even after all the reading I was nervous going into it. Overall I'm really pleased with the way things turned out, and I think my experience was enough that I'm qualified to at least chime in on the matter. I've got a few pics of the site with most of the work done pre-pool if you want to see 'em. .

Awww, I thought somebody else here could relate to driving all over creation with a drop hammer, proctor ring mold, portable camp stove, sample pans, lab scale, and a Ottowa sand cone in their truck.

Having the camp stove was nice, that way when you were in the middle of nowhere you could have a hot lunch, even if it was a bit dirty.

-dave