I just finished backfilling my foundation (about 7′ deep, mostly sandy soil). Someday, I will pour a driveway over this backfilled area.
How long does one wait until this dirt is considered “undisturbed” and can take a concrete slab?
I figured we would just let it rain on it for a while and maybe I would put some gravel on it and start parking there. Over several months that should do a nice job of packing it down.
MERC.
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Replies
I've always heard 7 years. I would think that you're depth would increase the amount needed...
Jon Blakemore
You can be good to go if you compact it while backfilling. Your plan is probably going to work fine by spring or so.
A seven year situation to me is when the definition of 'disturbed' is in application in wetlands areas or simnilar wherre the ecosystem and fragile flora need to re-establish themselves
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If you backfilled in shallow lifts, say, 10'-12" and compacted the soil in excess of 125% compaction (with a mechanical backfill tamper), you should be able to pour your driveway slab real soon. As an added precaution, if you can afford it, I would install a few #4 rebars at around 12" o.c. along with temperature steel. If you are still concerned about settlement, one practical solution to settlement near the foundation wall is to stub out #3or #4 bars out of the foundation wall (grout the bars solid into the wall approximately 6" into the wall, an extend them bout 12"o.c. 16"-18" out into the new slab. Wire tie the stubbed rebar to the slab rebar, lapping the bars 18 bar diameters (1/2" dia bars = 9"). This ties the slab to the wall, preventing the slab from pulling away, and will help keep the slab in place vertically just in case there is some settlement below the slab. Good Labor Under Correct Knowledge (Good L.U.C.K. to those of you from Rio Linda!)
How do you get 125% compaction?
A modified proctor is 94+%, and I have had spots test to 97%, but never over 100%.
Explain please.
Dave
It is impossible to get over 100% of a modified P.D. When this happen it is always because of a chenge in material and a new P.D. is needed.
We had a jumping jack here when we started backfilling, but we have been so wet here (NC) that the dirt had enough moisture in it to render the jumping jack useless. It just pumped the dirt up really.
So I said the hell with it and just threw the dirt in 7' high with no compacting. I figured the bottom foot or two is pretty much compacted already from the pressure of the dirt on top of it. Then if I just let rain and cars and bobcats work on it for a while, I might be allright in a few months. I'm in no rush to get the driveway in, so it's not a huge deal.
I just want to make sure I don't have to wait "years".
MERC.
i understand that re-cycled concrete has recently been approved for base material here in california for the freeway system.
normally under a section of concrete freeway they put "base", on top of compacted soil.
i have used the re-cycled concrete for driveways and it works great! in no time at all it seems to re-knit itself, a very tight gravel driveway
if you put some of that down where you want future driveway to be and then drive on it, trying to get heavy vehicles/equipment on it that should definitely help compaction and you will have a usable driveway right away
I wouldn't recommend pouring anything on the backfill for a looooong time, if you expect it not to crack or break up.
did I miss anybody saying sluice it??
make the backfill into mud and it'll be like concrete, 2 weeks later pour anything you want on top and it'll never settle.
learned this in 1951 when city contractor dug up our front lawn and gave a moneyed guarantee that there would be zero drop in the yard after they backfilled and resoded. . They were right, recall their backfill was quicksand consistency mud courtesy of the local fire hydrant.
21 days later, the sod on top, etc. , never ever noticed even a dip.
I knew a dip if there was one in the lawn, Pop paid me 25 cents to mow the lawn then.
That all depends what kind of soil mix it is to start with. Water amkes some settle in and some boil out.
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Hmmm....this is interesting thought. A lot of the backfill went in wet, thought it wasn't quite quicksand. But the jumping jack just mushed it aside and didn't do anything to compacting it. So maybe I'll be ok.
Since I'm not really in any hurry, I think I'll just toss gravel on it and drive over 10,000 times.
MERC.
let me try to explain soil 101
water, moisture, the liquid stuff, take up space, this moisture replaced the soil that should be there. Because of the hydraulic it cause the soil to pump, unstable. After awhile this moisture will evaporate, heat or just migrate to another spot. Once it does it will leave air voids in the soil. When a weight or force is applied to top surface, the air void will collaspe and settlement happen. If no force is applied it will bridge. That why the front yard did not settle but the driveway will. If you do not want to compact proper then once it settle just add more material. and apply as much force as possible.
Here the fact: it will settle. If your drive is poured and there is not enough strength in the concrete to bridge , The concrete will crack after awhile there will be a differnt in elevation between the sections of concrete.
Hey bud... if your backfilling, your project must be coming along petty good! Do you have your basement floor in yet? It helps a lot toward bracing the walls. I think your idea of mixing in some gravel and driving on it for a while will work out fine. Let it dry out and keep driving on it - maybe until late spring, early summer. 75 degrees is optimum for pouring concrete. Once you do pour, you may end up with a crack or two after several years, but provided you are not too hasty with placing the concrete, I think you will achieve reasonable results. What I have learned is that if the substrate is all of similar compaction, the slab will tend to float on the substrate and not go "south". If you want to add additional strength to the slab, sometimes the easiest bang for the buck is to just to make it thicker... form up the first 16' with 2x6s and order 3500 psi and you will be good to go. Be liberal with the control joints in your finishing. Raleigh Ready-mix has a sale on, where if you order twice as much you get to pay twice as much!! :-) Matt
Oh yeah, we are moving along. I've attached a current picture for those interested. The ice/sleet slowed us down some, but we seem be turning the corner on the weather here after the big rain on Friday. We backfilled Thursday until about 9PM, then tarped everything to keep it *somewhat* dry. The area beside the house is the place in question about the dirt settling. We dug out from the house about 7' and went about 7 or 8' deep. However, the driveway will cover most of the area next to the house so 1/2 will be "disturbed" earth and the other 1/2 on rock-solid undisturbed earth.
I think I will put lots of rebar in it to help keep it together. Fortunately I still have to pour a topping slab on my back porch so while the concrete truck is here I'll get him to drive over the filled area a few times. That 75,000 lbs ought to do the trick.
My engineer had also suggested doweling the driveway into the foundation, but I haven't decided if the driveway is going all the way over or not.
MERC
Is that black part the ICF with waterproofing on it? Look a lot different than the last pic I saw...
IMO, it looks better when you don't run the concrete up to the house. Leave an area for planting shrubbery. Make it at least 5' wide and make sure it slopes away from the house with a good amount of fall to get the water to run off properly. The only reason to run the concrete up to the house is if you are very space constrained. Matt
Yes, that is the waterproofing on the ICFs. I had them spray up onto the concrete decks about 12" and then I have a sheet of EPDM that I am going to lay down before setting the stone or pouring the topping slab (haven't decided yet).
I have lots of pictures of the project if you want to see anything in particular. I should post a picture of the structural concrete deck pour where we used the Paneldeck product. My back porch is a concrete slab that spans 15' and is 25' wide. It's all basement underneath it. Lots of rebar in that one.
Thanks to all for the replies.
MERC.
I should post a picture of the structural concrete deck pour where we used the Paneldeck product. My back porch is a concrete slab that spans 15' and is 25' wide. It's all basement underneath it. Lots of rebar in that one.
Yes, please.PAHS Designer/Builder- Bury it!
Posted in the photo gallery section...
http://forums.taunton.com/tp-breaktime/messages?msg=39793.1
MERC
I'm ignorant, so please forgive my confusion. If you are worried about settling, wouldn't tying your driveway slab into the foundation with rebar be about the worst thing you could do? Then if the ground under the driveway settles it will be putting pressure on the those spots in the foundation where you've placed the rebar. You'd end up with Falling Water without the post-tensioned engineering that saved it from being Falling House. I'd expect a driveway to have a lot more more movement then the house, since the driveway doesn't have footings below the frost line, so you are combatting both settling and heaving.
If you want to speed up the process going to 'undisturbed' soil, you could do what the road construction crews do here - add extra weight. They pile dirt up on the new offramps and bridge foundations for a year or so, then scrape it down to where they need to be to start the road base. Seems to work pretty well. Driving on it might do this, but I wonder if you'd only compact the spots where your tires go, instead of the whole slab's worth.
I can see your concern, however my foundation is 8" ICF foundation with about 9 miles of rebar in it. I live in NC so we don't have a lot of ground freezing and heaving. If the ground settles and the slab spans it, then you don't worry about heaving.
I do like the idea of piling more dirt on it. If I take the drive on it approach I would plan on making sure I shift around the parking to make sure the wheels do the work all over. Then I would put a compactor on it before I poured.
MERC
Yes, Temp Steel is Woven Wire Fabric. It is just another term for WWF, I call it that sometimes to differentiate it from reinforcing steel. Often, I hear people commenting on WWF as a type of reinforcing steel. I consider rebar as being structural steel.
Your are correct on the P.D. About the best you could expect would 96-98% modified Proctor or 100% standard Proctor. I guess you would be there a long time trying to achieve 125%!
I knew that. I was just giving him a chance to correct his post, politely.
Figured you would do it right away, and since he is pretty new......
Arktect, is pretty sharp,.. he corrected right away.
Dave
Me speaketh out the wrongeth sideth ufff my mouf... see the correction I added.
Just curious what you are calling "temperature steel" is that the same as WWF? No - not those fat muscle head guys wearing shorts that are too small :-) - I mean that stuff that comes in rolls or sheets... Matt
Yes, Temp Steel is Woven Wire Fabric. It is just another term for WWF, I call it that sometimes to differentiate it from reinforcing steel. Often, I hear people commenting on WWF as a type of reinforcing steel, which it is NOT! I consider rebar as being structural steel.
The backfill at my house has been settling for 40 years.
just go rent a jumping jack and pour next week
If you find any dinosaur tracks in it, you can figure it is "undisturbed"
Joe H
Nuts! I wouldn't walk within a mile of that place....Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
For backfilling to support a slab I always specify 97% compaction at optimum moisture content. As described in other posts, the compaction must take place in relativley short lifts, not at seven feet! Your installation will continue to settle for years.
I would want the driveway to be floating, that way if it does settle it would not hurt the house. I have never heard of anybody pinning a driveway or patio around here. With the concrete heat and cool it expands and moves. I would want my house isolated from this.