Concrete Slab For Metal Building

[FTCKUBOTA]

I am adding onto a metal building I have. I am adding a 30x80 addition onto the existing building. I had to add fill dirt to bring up to grade for the slab. The dirt i used has sand clay mixture mostly sand seems to pack very well. I had to fill 3 to 4 foot thick at the most. It has been in place for about 2 months and has had a bunch of rain on it. My question is what is a good way to tell if ground is compacted enough to put a slab on it. when the area is dry it seems very good when it is wet it seems a little spongey

I am going to pour a 6inch slab with rebar every 18inches with wire also and gravel and plastic

thanks for the input

 

[Schemp]

I am adding onto a metal building I have. I am adding a 30x80 addition onto the existing building. I had to add fill dirt to bring up to grade for the slab. The dirt i used has sand clay mixture mostly sand seems to pack very well. I had to fill 3 to 4 foot thick at the most. It has been in place for about 2 months and has had a bunch of rain on it. My question is what is a good way to tell if ground is compacted enough to put a slab on it. when the area is dry it seems very good when it is wet it seems a little spongey

I am going to pour a 6inch slab with rebar every 18inches with wire also and gravel and plastic

thanks for the input

The only way to truly tell is to hire an engineering firm that does soil testing, hopefully for no more than a couple of hundred bucks. 95% compaction is an elusive animal even for the experienced. It should have been backfilled in lifts appropriate to the material, moisture content, and the machine compacting it. If you used a small plate tamper, doing 2 to 4 inches at a time, running over it a million times, you might get compaction on a good day.
You didn't say what was on it when it seemed spongy. If it was your footprint, obviously bad compaction. If it was your tractor and it drops a couple of inches, bad compaction. If it was a concrete truck full of gravel and it drops no more than an inch, good compaction.
If it is going to be a monolithic slab with thickened edges for your building foundation, and the bad areas are under the foundation, you're probably going to have to dig it up and put it back right, because your inspector should catch that if he's doing his job. No matter how much you run over it with a compactor, you'll never affect what's down three or four feet. If your slab is going to be isolated from your footers, the bad areas are small and under the slab only, and you don't mind a little cracking, you might be able to get away with it, if you not going to be driving huge equipment on it. You could even tighten up the rebar spacing on the bad spots to twelve inches on center and go with a #5 or #6 rebar, but you'll have to decide which added expense you'd rather have.
Mother Nature will eventually compact it herself, but maybe in two to five years, not two months. Remember, even at 95% compaction, a four foot fill has the potential to sink another two and a half inches before it becomes 100%.

 

[flusher]

I am adding onto a metal building I have. I am adding a 30x80 addition onto the existing building. I had to add fill dirt to bring up to grade for the slab. The dirt i used has sand clay mixture mostly sand seems to pack very well. I had to fill 3 to 4 foot thick at the most. It has been in place for about 2 months and has had a bunch of rain on it. My question is what is a good way to tell if ground is compacted enough to put a slab on it. when the area is dry it seems very good when it is wet it seems a little spongey

I am going to pour a 6inch slab with rebar every 18inches with wire also and gravel and plastic

thanks for the input

Doesn't seem very stable to me.
I would have built a concrete retaining wall with the top of the wall at the floor level of your existing builting and filled it with rip rap and smaller size crushed rock and then build the slab.

Good luck.

 

[Egon]

95% compaction is an elusive animal even for the experienced./QUOTE]

Do you say that packng it with my Tractor Tires Isn't good enough??:laughing:

 

[Deere Dude]

I wouldn't think would dig anything out, but i would consider a man with one of these 3-4' driving rollers with a hydraulic vibrator to drive over the thing a few times. It should cost only a couple hundred bucks and it will get as hard as it's ever going to get. I had one for my pole building and when I had to put a sewer line in I had to almost get a pick to dig it up.
The only difference I can see is I don't have sand, but subsoil which here is clay and a few small stones. Mine was about 18" thick.

 

[Egon]

Hate to say this but with clay it has to layed in in layers and packed with a lug type packer so the layers bind together. Jut vibrating from the top down may not do much.

Vibratory works well with granular materials though.

 

[Hooked_on_HP]

There is no good way to compact 3-4' of fill at once.As others have stated it needs to be done in lifts. Since the fill is already in the only thing you can do is wait. Over time it will tighten up. I would wait at least a year. If you know any one that works for an engineering company they could test the compaction for you. I have seen old timers check compaction by driving a steel rod into the ground and seeing how hard it drives in the filled area compaired to the undisturbed ground.
Bill

 

[Egon]

With clay it's usually good when the packer stars to walk out.