We have a hole in the ground! New O/B in Queen Creek, AZ

[Copperhed51]

After a bunch of saving and planning, we have begun construction on our owner build pool. Excavation went smoothly, gas is done except for final hookup, and the equipment is in the garage. Plumbing and rebar are scheduled for this week. Electric and shotcrete will hopefully happen next week. After that, we'll tackle decking while the shotcrete cures before getting plaster/pebble.

How long is it recommended to wait before working on coping and waterline tile? The plaster company recommends waiting 28 days before applying plaster, but I'm unsure of cure time prior to tiling.

I do have a couple of concerns. During the dig, the excavators dug through a layer of very loose, sandy soil around 7' down. The deep end will be 8' deep, so the bottom will sit below this loose layer. The shallow end will obviously sit above it. How concerned do you guys think I should be about differential settlement and future cracking of the pool? I've contacted some engineers, but none seem too interested in working with me on it. I'm also thinking of bumping up the rebar to 6x6 for the entire pool to try to make for a stronger shell. One engineer I talked to said it may help, but there's no guarantee it will. The extra rebar will cost me $850. Any thoughts?

I'll try to get some pics up soon. Any good photo hosting site recommendations?

I'm also looking at The Pool Cleaner vacuum to get me started. I'd like to get a robot eventually, but the budget is bumping right up against the limit, so I'll settle for something to get me by for a couple of years. The pool is approximately 18x30 plus a 14x6 baja/sun shelf. Is The Pool Cleaner a good choice and what do you recommend between the 2-wheel and 4-wheel versions?

Thanks!

 

[JamesW]

For coping and tile, I would suggest that you wait as close to plaster as possible. Maybe within about a week before.

For rebar, I would suggest #4, grade 60 on 9" centers.

For the concrete, I would suggest an 8" to 9" thickness with a strength of 5,000 psi.

If you feel that the soil is an issue, you should get a geotechnical engineer to evaluate and advise.

You might need piers if the soil is not considered stable.

Rebar doesn't really prevent cracking unless rebar is prestressed because rebar doesn't really begin to help until it's under tension.

Rebar will help reduce the size of cracks and reduce the separation of the concrete either opening or shear sliding.

It's always best to have an engineer design a plan for your specific project. Using "standard" designs only works for nominally standard projects.

Note: Make sure that all inspections are completed before scheduling shotcrete.

 

[Copperhed51]

Thanks for the reply, James. I have been in contact with a couple of geotechnical engineering firms to try to get some help, but they don't seem too interested in getting involved so far. I would like to do this right, but we are going to be stretched on budget as it is. I'm pretty worried about how many thousands of dollars we will end up spending on revised plans and remedies. Maybe piers aren't as expensive as I'm envisioning, but I really have no idea.

I will talk to the rebar sub about stepping up to #4 and loosening up the spacing a bit. Maybe that won't drive the price up too terribly much. I know we are basically engineering by the seat of our pants at this point, but do you think the entire shell should be done in #4 on 9" centers or just in certain areas? Thanks again.

 

[Copperhed51]

Here is a picture of what I'm concerned about. Maybe I'm freaking out over nothing, but this stuff is very crumbly. I have no idea why this keeps loading upside down.

 

[JamesW]

The exact rebar specifications should be designed by an engineer for the project. My suggestions are just general specifications.

While rebar can be helpful, tight spacing and big diameter can increase "shadowing", which is where concrete does not get behind the rebar properly and creates weak spots.

 

[Arizonarob]

Copper, is it just a certain amount of loose soil, like 2 ft or so, then goes back to the firm soil we have here below it?
I’m thinking somewhere in the past, that area may have been a dumping zone for excavating projects going on.

 

[Copperhed51]

Copper, is it just a certain amount of loose soil, like 2 ft or so, then goes back to the firm soil we have here below it?
I’m thinking somewhere in the past, that area may have been a dumping zone for excavating projects going on.

Yep. According to the soil report, my section of the neighborhood was built up with about 7 feet of compacted fill. There's then about a foot or foot and a half of loose stuff, then back to normal looking soil. I may be freaking out over nothing, but I dunno. $850 of extra rebar may be worth it for a little peace of mind, but may be completely unnecessary or not enough. I just can't get an engineer to do much for me. I'll get pics up of the entire dig soon. I probably also made a little mistake going from 4' to 8' deep on a 30' long pool. The slope gets a little steep, but I'm also not sure that's going to bother me much. Nearly half of the pool will be pretty easy to stand in and the rest would be too deep to stand in anyway, so a steeper slope is no big deal. As of now, I'm moving forward with plumbing in the next couple of days and am still mulling over the rebar options.

 

[Arizonarob]

Ok, so the key word you used was “compacted”.
When they raised up your neighborhood (it most likely flooded during monsoon rains) to build on, all that soil was compacted down. So because you are disturbing it from excavation, it’s turned loose again. I’m by no means an expert, but I’m with James on the extra rebar and you should be fine.
Keep seeing if you can get an engineer out there to firm up your suspicions, and in the mean time, see if you can talk to any of your neighbors that have a pool. They may have run into the same thing you’re dealing with, and may have some insight.

 

[Copperhed51]

Ok, so the key word you used was “compacted”.
When they raised up your neighborhood (it most likely flooded during monsoon rains) to build on, all that soil was compacted down. So because you are disturbing it from excavation, it’s turned loose again. I’m by no means an expert, but I’m with James on the extra rebar and you should be fine.
Keep seeing if you can get an engineer out there to firm up your suspicions, and in the mean time, see if you can talk to any of your neighbors that have a pool. They may have run into the same thing you’re dealing with, and may have some insight.

Thanks Rob. The portion of soil that they filled and compacted is in great shape. I think we've dug below that soil and are into the old, original soil. Had I kept the pool at 5' or less, I wouldn't have ever reached this loose stuff. I think things will turn out ok with the extra rebar, but an engineer's opinion would be nice to have. I'm going to keep reaching out to them. I really think the soil will be ok. I am a little concerned that a lot of the soil on the bottom of the pool in the deep end is very soft. The excavators seem to have just spread the sandy soil around to get things level and the proper depth. When they were digging, it was like they were digging in a sandbox. It was hard to get everything out of the hole without a bunch of sandy soil just spilling everywhere. When I walk around in the excavated hole, my feet can sink down an inch or two into the sandy soil. I wish I had more success getting a soil sample taken before excavating. I could have chosen to make the pool more shallow and potentially avoided a lot of the issues.

 

[Copperhed51]

Here is the soil we were dealing with during the dig as we got deeper down:

And some general pics of the completed dig:

 

[PoolguyinCT]

The risk with a sandy dig , is the shell sinking.

More steel will not compensate for the possible deficiencies of a sandy soil.

- you will get your these answers some day, best to get them now.

Be glad you haven’t shot yet & now is the time to have your soil deemed competent or make corrections.


*** striated soil is a major red flag in my book.
I just realized you are OB, probably why nobody is running over to test for you. Have your shotcrete contractor make the call for you.

 

[Copperhed51]

I just realized you are OB, probably why nobody is running over to test for you. Have your shotcrete contractor make the call for you.

I'll get in touch with them and see if they can help. They are probably the biggest shotcrete contractor in the valley, so they can point me in the right direction.

 

[Arizonarob]

Yeah, I didn’t realize how sandy your soil is,(kind of strange for these parts) that would worry me.
You need to get real answers on that before moving forward. (If your sinking down into it just walking on it, imagine the weight of the pool)

 

[JamesW]

I suspect that you're going to need some sort of remediation plan to provide a stable base for the pool.

Maybe piers, but an engineer would be the person to determine what, if anything, should be done.

 

[Copperhed51]

Yeah, I am fairly close to the QC Wash, so maybe that has something to do with it. I wetted the bottom of the dig a little bit yesterday and doesn’t sink much at all when I walk on it now, but that’s maybe as concerning as it is comforting. Hoping to hear from some folks today to get this looked at. I’m thinking helical piers could be necessary, but that’s going to run us into the thousands of dollars of engineering and work. We definitely didn’t budget for that. All of the PB’s in the area warned us about hard digs, but nobody ever mentioned soft digs. It wasn’t on my mind at all.

 

[Arizonarob]

It is really strange in this area to have loose soil like you do, 99% of the time you need a jackhammer just to plant a shrub around here.
Makes me wonder where they trucked the fill in from.

 

[mslaman]

You definitely need a soils engineer. That area is very well know for fissures. Fissures were big news in QC about 10 years ago.
Helical piles are very expensive in the valley. I just had them priced for a project at AZ Heart Hospital. Only one company qualified to perform the work in Maricopa County.
However that is big commercial construction. helical piles are mostly placed on the coast.

A quilified soils engineer would would be best before you stress yourself out worrying about speculations.. get the facts. Then act. They will recommend the best solution. Hard to be sure just by pictures and gut feelings. I believe you have very legitimate concerns that should be investigated before continuing with your projects.

‘Unknown issues that manifest themselves during construction are always irritating. But you’ll get through it.

 

[Copperhed51]

Thanks for the reassurance I’m doing the right thing. Geotech engineer should be here tomorrow. I’ve checked the fissure map and we aren’t close to any known fissures, luckily. I really believe this is mostly sand from the QC wash, which is close enough to have deposited all this sand before the neighborhood was filled and compacted. The plumber and gas guy said they see this a lot in my area. They didn’t seem concerned when I asked them about it, but it’s not their pool and $

 

[Copperhed51]

The soil guy has given us his blessing to continue along with some mitigation strategies I've been implementing the past 2 days. The situation is not perfect, but we should be ok structurally. Other than that, plumbing is getting closer to completion. I'm amazed they just have one guy out here doing the entire job. This plumbing contractor is regarded as the best in the valley. I had them plumb the main drain and skimmer separately, so I had to run and grab an extra 3-way valve for that, but things seem to be going smoothly otherwise. The back yard looks like a war zone. I'm ready to get some shotcrete in this hole so I can hopefully begin to relax a little bit. Minus the soil conditions, the OB process hasn't been too bad. Having this hole open to the elements for an extended period of time is just somewhat scrary. Anyway, here are a couple of plumbing pics. If you see anything weird, let me know. It's pretty tough to tell where everything is going. The black pump is the main filter pump (Pentair 011056) and the tan is the feature pump. The sub who got me my equipment could only get the main VS pump in black, but I don't care much about that. It's not exactly planned to be a show piece.

I should mention that I'm incredibly glad we got the gas line run before the plumbing. That's a lot of PVC the gas sub would have had to run the line under and potentially break/cut. The gas line runs to the heater and also branches off under the plumbing to stub out for a BBQ. We had him size it to add a fire pit and maybe fire bowls in the future

 

[Copperhed51]

I've got a question about the plumbing. The plumber is off getting parts, so I went out and took pictures so I could have documentation of where everything is and where it goes before it's covered in dirt. I noticed the valve on the filter outlet goes to the heater, then the outlet from the heater goes to the SWCG and is looped back around to that same valve at the filter outlet. The valve would allow me to shut off the filter outlet entirely, or shut off the looped return from the heater. Is this right? I would think it would be a bad idea to be able to shut off the filter outlet completely in case you accidentally do it with the pump running. I'd like to notify the plumber asap if this is a problem. Thanks for any help.