Pre-contract questions (DFW/expansive soil experts needed!)

[Tuttle]

Hi all,

After discussing a pool for many years my husband and I are about to pull the trigger on our contract for an in ground gunite pool. I've been lurking for months but had a question for all of you DFW/expansive soil pool owners.

The dream layout (for me) is to have the largest dimensions of the pool run the length of our house, with the spa on the right side of the picture below. I have been concerned by the rather sharp slope to the left side of the picture. (I apologize for the size and angle of the photo. I don't currently have a picture that shows a better view of our lot.) Our first choice is going to build up that side with a retaining wall. The other pool builders all oriented their renderings in a perpendicular fashion to our house, one saying he would never build near a slope of that size.

My question is how concerned should I really be with future movement and/or significant cracks in the gunite on the lower side of the yard (with a retaining wall)? Are we signing up for a nightmare in the making if we go with our first choice? Thank you for any help!


(P.S. Ignore the busted windows and patched roof. Our town received hail over 5+" in diameter this spring. This picture was used as documentation for our insurance company.)

SaveSave​

 

[gocubs418]

I've heard it depends on what part you live in. From the hail damage and lot size, I'm going to guess Murphy/Sachese/Wylie. I haven't heard of bad soil out there.

My PB pretty much "threw in" chemical injections because he insisted yet I told him I didn't want it.

I've heard all Texas soil is bad because of the heat and the constant expansion and contraction and I heard that nothing will go wrong. All I know is I am chemically injection and my PB will warranty my shell cracking or popping out of the ground.

Good luck.

 

[pooldv]

How much drop is there? Will the pool bottom be sitting on undisturbed soil? The key to managing movement is constant moisture level. Our pool cracked and leaked the first winter because of the drought and dry winter the soil contracted. I installed a micro irrigation system around the pool and it solved the problem for a few years. Then after all that rain last spring I was slow to turn it back on and it dried out faster than I thought and cracked again, no leak that time. So, I pretty much leave it on all the time now at least a little. I can see the soil contracting away from the pool and turn it up to stop it. We are on a slope and the police sticks out of the ground 18-24" on the downhill side. Pics in build thread, link in sig.

 

[ntobik]

I'm not from Texas, so I don't know Texas soil. But I live in Western Pennsylvania where I'm not sure there is a flat piece of anything anywhere. Our pool was dug out of a hillside and we have a 7-8' retaining wall holding the hill back. The wall is 40 years old and has moved some, in this area all walls move. The hills are in constant (slow) motion.

The pool was dug out of a newly flattened area. The pool is a giant concrete shell and we have a vinyl liner for it. When we renovated the pool I had a chance to inspect the concrete itself. There were a few hairline cracks, but for a 30yr old pool built into a hillside it looked fantastic. I like having a liner because then I'm not worried about chasing cracks after a bad winter.

The question I'd have is what is the soil like? Not the topsoil they dumped, but the real soil that sits a foot or two under the grass. If it's clay or rocky you will be fine. If it's very loose then I'd be concerned. Although there are a lot of people on this board with pools in Florida where the ground is just sand.

Instead of building up why not have them dig down? It's a lot easier to level the area and have a step down from your patio verses building up a retaining wall.

If you're worried about retaining wall strength go Versa-Lok or a similar technology. You should see some of the wall insanity we have around here. I just had some walls put up, one is holding back 7' of a dirt hillside with ease. The Versa-Lok has pins to hold the blocks together. Don't let anyone convince you of a stacked block wall. Stacked block will eventually fail. Also have the builder dig an extra foot and set the wall footer on concrete. The last item of importance is make sure there's proper drainage behind the wall.

All things considered I'd just have the builder give the backyard a bit of a haircut. At most you'll end up paying for a bit more labor and a few more truck loads of dirt. You can mitigate that cost if you know someone in your neighborhood who needs clean fill. Or if the builder can just shift the dirt around in your yard.

 

[Caco]

Personally if I was to build a retaining wall in moisture sensitive ground I would use gabion baskets (big wire mesh baskets with loose rock fill). Easy to put drainage behind and through to control moisture levels, like this

I would also make contact with a local geotechnical engineer and get him to do some basic testing. Things like scalas for CBR (how much load the soil can take) Plasticity index and linear shrinkage to determine how the soil reacts to moisture. If you tell them what you are trying to do they could tell you what tests you need. Should be about $1500 for a whole raft of tests that will give you certainty, otherwise everyone is just guessing what you need