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Stem wall fill dry out time before slab pour

Bw1LL1s

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Mar 2, 2024
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Greetings to everyone. I’ve lurked on here for sometime, but never got around to registering. Yall have some beautiful shops, and there has been a ton of useful info on here. I’ve been in the process of planning/building a red iron building over the last 4 years. Dreaming for 30 🙃 The rain has been a huge back up the last few months here in VA. I could say it has almost been as big of a hold up and pain as the county permitting process. We have finally manage to reach the point of having the stem wall prepped, fill/compacted , and ready for the slab pour. Since it was completed we’ve manage to have a couple more hits of rain. To evacuate any built up moisture/ additional rainfall we drilled a 4 inch core against the footing through the base of the stem wall at the rear corner. In the process of filling the foundation with structural fill we sloped it towards the drain, and used layers of aggregate/fabric to percolate better that way. Any saturated fill that was inside walls during this process was skimmed and either dried out or dumped outside walls for backfilling/sloping later. I have at least 8-10” of compacted aggregate covering the entire surface. There will also be a substantial swale with drainage pipe/stone dug along the low left side of foundation. As it sits now there is no breech over walls even in a heavy rain. After substantial rain night before last water is still percolating steadily out the core hole. We are leaning towards putting plastic down and draping it over the sides temporarily to keep any extra rain off until slab is poured. I’m debating as to how long I should wait before slab is poured if I need to at all. If water stops percolating out the drain, and we are able to get it covered should I be good to go? Or would it be better to let it have more drying time. People seem to be all over in regards to this. For what it’s worth there will be a minimum of 6” of slab. This foundation is completely overbuilt to say at the least but between codes, somewhat subpar geotechnical reports, location, and slope there wasn’t much of a choice. Luckily I have some contacts in concrete as I’m in the concrete demo/cutting business. I also plan to be here long term as the home has been in my family since childhood. Otherwise I’m not sure this would have been feasible cost/time wise.
 

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Hank11

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I don’t know the answer for sure, but I am envious of your very nice work so far. I would be inclined to pour the slab now or soon.
 

Shiftless

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Mar 9, 2014
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East Bay SFO
Looks good to me.
Did the design engineer voice concerns about the unsupported (no retaining wall) steep slope on that downhill side? I assume you did well compacted fill.
Maybe it’s not required with your particular soil. Pardon my possible over abundance of caution.
 

PCustoms

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VT
I don’t know the answer for sure, but I am envious of your very nice work so far. I would be inclined to pour the slab now or soon.
Certainly beefy!

What is the fill? I'd think as long as your hitting your compaction #s (based on the robustness I see I am assuming you tested) then good to go. @ConCretin is pretty much the site expert, let's see if he chimes in.
 

Dig Doug

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Apr 16, 2018
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Put down some 6 mil visqueen let it over hang all the sides, that will capture any rain and not perk down to your subgrade, then pump out any standing / puddling water on the visqueen w/ a small sump pump.

double edge sword
wait for it to dry out vrs pour the slab

not sure how much rain you got
but
I would pour it asap !

you have a vent core and rock in place, is your soil expansive/ clay
 
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Bw1LL1s

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Mar 2, 2024
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Besides some poor soil the slope is why we did such an overbuilt stem wall. The rebar specs were completely over board, but it’s what he (my engineer) felt was necessary in order to appease the inspectors,( if not shock them) lol and guarantee it was sound. Kind of screwed myself with the geo report and their absolutely ridiculous recommendation of 12 2’x20’ piles. One for each structural beam. After that I hired a retired engineer I knew I could trust for the stamp. It’s a floating footing as much as it is one that’s held down. Footings are 6’ wide 18” deep on 12” compacted aggregate. Walls are 18” thick as well 5’ tall on two low sides and 3’6” on other. All of it is tied together with a huge amount of rebar. There will be drains on two sides with a swale on one with the drains below that as well. All 4 sides will be covered with fabric and stone. The back low side will just be stone on the ground as a parking area. I have a road cut around to it, along with the option of building it up eventually if I decide to. The fill was trucked in as far as what’s in wall. Whats not stone is structural fill. Lots of hard clay here on site but also silt and organic material. This was all dense forest 4 years ago. Probably took out 15-20 large trees. It backs up to a creek valley. It will be a 40x70x14-18”overhangs all 4 sides/gutters with 12x13 doors center of gable ends (drive thru) 10x10 rear of downhill side culvert over swale and a 7x10 to the right of 12x13 on frontside of building. I wanted as much access as possible for ease movement. I have several vehicles that will be kept here along with a tractor. I plan to have a full bar/rec area and a 2 post lift with a work area easy to access. The site was a challenge not to mention the county. I had to factor in aesthetics as well. This is a residential area and it needed to flow. Here are some picture's of the site and footing work. As I said if I didn’t have the commercial concrete connection it wouldn’t have been feasible to do. If there’s one area I have to go overboard on I’d rather it be the foundation. I also wanted this to be 100% legit and have the paper work should I ever sell.
 

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My Old Tools

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Jun 4, 2014
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Hamrick Lake, TX
Yours is built heavier than mine by a good 50%. Mine has been in the ground for 7.5 years with no cracks.
 

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PCustoms

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Curious why such a heavy continuous footing and stem wall for a red iron building.
 
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36truck

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Jul 13, 2010
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With everything you have done in your footings you should be good to go. I like the over build. That will keep you going for a 100 years.
 

Hank11

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Aug 19, 2019
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Tennessee
I was guessing it to be half that size or smaller -- now with the dimensions and pictures I am really impressed. Looks like something for a nuke plant.
 
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Bw1LL1s

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Mar 2, 2024
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😂 nuke plant. I’ve been been referring to it as the foundation for a 6 story parking deck or fallout shelter. I appreciate the feedback y’all. (My old tools) I love the steel mezzanine in yours. I plan to do something similar down the road. The lake view is awesome too! I love the creek behind mine. Completely overbuilt, but I really had no choice to make it happen. In all honesty the 4+ years I’ve put into it have been stressful, not to mention a strain with old lady (as far as my time). 😩 in order to keep cost under control and make it work it was necessary. Now that I’m finally rounding the corner it’s a relief. As I said it’s been a dream my entire life. I’m a huge car/truck guy and it will be a sanctuary/man cave as much as it will be used for work/storage. I had every intention of doing the erection on my own as well but I’m gonna throw the towel in here. I found some guys that do excellent work. They specialize in steel building erection also had a fair price. They were even willing to unload the building for me at their farm. They will bring in pieces as they erect it so it’s not laying around here. With the 4 to 12 pitch and steep access on sides it won’t be the easiest job out there. Ithaca steel is who I went thru for the building, and I will say so far they have been great. Steve my salesman has worked with me for years on this before I jumped.
 
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Bw1LL1s

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Mar 2, 2024
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Dig Doug, i appreciate the advice. Yes there was a bit of expansive clay around. The rain set a record here in Chesterfield/Richmond VA area for Dec. it has been very wet. It looks the last couple weeks to finally be letting up. We plan to move asap on slab. I just figured I’ve waited this long to do it right. Also thought I’d reach out to you guys on here and get some input 👍🏻
 

ConCretin

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Central Maine
I'll second the comments regarding the robustness of your stem wall reinforcing. Very impressive. Probably overkill as you acknowledge but we do love our overkill on the GJ now don't we. With regard to your question about placing the slab, I think you're fine to go ahead and get it placed. Most if not all of the settlement caused by water has already occurred. You are always going to get some settlement within a fill but as long as the base provides uniform support for the slab, you'll be fine. Good luck with the rest of the build and keep us up to date.
 

C-S-H

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That is quite the massive foundation structure. With the 6' wide footings and the 18" wall I assume that your building is a gable frame structure and the wall has to take all the lateral thrust? So the slab will be floating and not serve as a tension tie? What type of aggregate gradation is under the footing, and is there a geotextile under it? If open graded aggregate was used with no geotextile, then I would expect some settlement of the structure in the short term. In that case I would want to cast the slab after the building is completed to allow some settlement time.

Also, since the subgrade under the future slab is wet, and you mentioned expansive clay, I would want some drying time before the slab is cast. The clay subgrade under the structure will come to an equilibrium moisture content similar to the clay down deeper. I have seen slabs move both up and down over the long term. I think your slab would move down over the long term given the wet soil conditions now. Will the foundation and the slab settle the same? Who knows.
 

PCustoms

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I'll second the comments regarding the robustness of your stem wall reinforcing. Very impressive. Probably overkill as you acknowledge but we do love our overkill on the GJ now don't we. With regard to your question about placing the slab, I think you're fine to go ahead and get it placed. Most if not all of the settlement caused by water has already occurred. You are always going to get some settlement within a fill but as long as the base provides uniform support for the slab, you'll be fine. Good luck with the rest of the build and keep us up to date.
And there you have it, pour away.
 

Beemer

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Northeast
Nice concrete work, no doubt a commercial effort.

Luckily we don't have much clay to deal with here but I seem to recall foundations were not put on clay and slabs got a very thick layer of compacted structural fill over the clay. When I note foundations were not on clay, alternative designs were used to get the loads through it. Those jobs were on a different scale than yours though.
 
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Bw1LL1s

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Mar 2, 2024
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That is quite the massive foundation structure. With the 6' wide footings and the 18" wall I assume that your building is a gable frame structure and the wall has to take all the lateral thrust? So the slab will be floating and not serve as a tension tie? What type of aggregate gradation is under the footing, and is there a geotextile under it? If open graded aggregate was used with no geotextile, then I would expect some settlement of the structure in the short term. In that case I would want to cast the slab after the building is completed to allow some settlement time.

Also, since the subgrade under the future slab is wet, and you mentioned expansive clay, I would want some drying time before the slab is cast. The clay subgrade under the structure will come to an equilibrium moisture content similar to the clay down deeper. I have seen slabs move both up and down over the long term. I think your slab would move down over the long term given the wet soil conditions now. Will the foundation and the slab settle the same? Who knows.
Yes it is a gable structure and the wall will support a 100% of the weight. The slab is not gonna be structural in any way. It will have an min. Thickness of 6”. Any expansive clay was dug out the best possible. The rear right corner by concrete culvert/low corner had to be dug out the deepest. Originally my engineer called for just 3’6” walls all around, but when digging down we changed it to 5’ on 2 sides the right and rear to make sure we had good elevation and reached a good base. It was the lowest spot in elevation to begin with. There was a fairly deep vein of nasty/jiggly/organic material that ran across that area fairly deep. After clearing trees and stumps/topsoil I excavated down until I hit good soil. It was fill back and compacted with good stuff a couple years ago at this point. The wall and footings have been done since September. We are gonna cover it like you said and hold off at least a 2-3 more weeks.
 
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