subbase fill for pole barn slab

[Buck455]

Hi all.

I'm looking for some advise on what material I should be using to bring up the grade underneath a future pole barn concrete slab. I'm building a 30x48 barn in southeast Michigan, and I have about a quarter of the area that tapers from 1' to 4' undergrade. Also, I have two trees to pull and fill.

Can anybody suggest what the proper fill material(s) should be to bring up the grade? My plan thus far is to remove the top 4-6 inches of sod and top soil, dig out the tree stump and roots, level what I can with a bobcat and compact, then bring in the fill.

Thoughs?

Thanks in advance!

 

[gumshu]

Depending on your terrain, you may need to cut a key-way to get proper compaction on whatever fill material you decide to use. There are a variety of fill materials you can use. Stay away from any top soil or dirt containing organic decomposition. Subsoil is probably cheapest and 95% compaction is typically adequate. You can use a "sheep's foot" or tractor to compact the moist soil.

 

[BHD]

I would most likely use gravel

 

[LD1]

As gumshu said, sub-soil is probabally the cheapest. But it needs compacted somehow. That requires either a sheeps foot, or doing it an inch or two at a time and driving over the whole area with the SS or tractor before the next inch or two. Either that, or wait a few years for things to settle on their own before the pour.

IF neither of those is what you want, then gravel. Something like 304's (or what others call crusher run). But it will take alot. I figure about 80 yards just to make up the 3' difference in elevation. And about another 20 yards if you want 4" of base on top of that. So 100 yards, you are looking at about 150T of limestone or about 200T if you go gravel. Either way, you are looking at about $2000-$3000 of stone.

Two other options is either cut the whole hillside out down to virgin ground.....or

Only cut about half of the hillside out, and use that dirt to build up the lower half of the hillside. But again, you have to compact that lower section.

 

[Buck455]

Thanks for the input guys. Sand is pretty cheap in this area, would that be a viable option for that much fill?

 

[LD1]

Thanks for the input guys. Sand is pretty cheap in this area, would that be a viable option for that much fill?

No. I wouldnt use sand. Not unless you had a SOLID way to capture it to keep it from squishing/washing out from underneath the concrete.

Would you pour a concrete slab on a beach and expect to to hold up to driving on without cracking??

 

[Buck455]

That's fair. I will be backfilling at least 5' around the barn with sub soil/topsoil.

 

[DJ54]

Are there any gravel banks near you..?? Such as like Bank Run gravel..?? That's what I used for my two new buildings I just had put up. Put it in in 8" lifts,and rolled 3 times with my Massey 180 with a carry-all on back with all that would stick on there. I hit a decent seam of yellow clay, so mixed it @ about 30%. When I backed in with my 1 ton dump, with approx. 4 tons on, it just left a tire print, and it did not sink in. When they dug the holes for the poles, they used a Bobcat with an auger w/an aggresive bit. He had to rear back on the auger to dig the holes... Last Friday when my buddy poured the floor for my new shop, he had to use a 5 lb. sledge to drive in 1" steel form pins. I'm pretty confident it's not going anywhere.

Not sure what you native soil is below the topsoil, but if there is some shaley clay, that is excellent fill, if you have a knob you can strip the topsoil from, then remove enough clay to fill, then reclaim the area.

 

[nybirdman]

We are in the process of doing a pole barn ourselves(my son-in -law) and he is an engineer.Removed the top soil and leveled with my tractor/box blade.Bringing in "crusher-run underneath.30x40x12.Estimated cost of $9,000 plus the stone which will be about $350/20 ton loads.Planning on concrete in one bay next year.

 

[BHD]

be careful on using clay soils as most clay is expansive and will swell and shrink depending on moisture content,

 

[cyamaha2007]

Look into concrete washout. It is free around here. I paid for the owners fuel $50 a tractor trailer side dump load. Its easy to work with and sets up hard as a rock. Concrete washout comes from redimix plants concrete plants. When a truck comes back with they clean the drum with water and dump the watery concrete on the washout pad. They let it dry and push it up into piles. I just went to the plant near me and asked if they sold it he was very nice and agreed to drop off 10pluss loads. Heres a link to my 36x56 pole barn build on another site you can see the washout im talking about. My diy 36x56 fab shop "pic heavy" - The Garage Journal Board

 

[PhysAssist]

Look into concrete washout. It is free around here. I paid for the owners fuel $50 a tractor trailer side dump load. Its easy to work with and sets up hard as a rock. Concrete washout comes from redimix plants concrete plants. When a truck comes back with they clean the drum with water and dump the watery concrete on the washout pad. They let it dry and push it up into piles. I just went to the plant near me and asked if they sold it he was very nice and agreed to drop off 10pluss loads. Heres a link to my 36x56 pole barn build on another site you can see the washout im talking about. My diy 36x56 fab shop "pic heavy" - The Garage Journal Board

For what it' s worth, you may not want to disturb too much or too deeply into your base.

We're in a frost area (between Buffalo and Rochster, NY), like you are, and every one of the contractors we got quotes from agreed (independantly) that the footings needed to be sunk below the frost line, (='ing in my area) 42" into VIRGIN or UNDISTURBED soil, meaning, if you regrade it, they have to go that much deeper with the footings.

We are regrading,but only by filling in; first with clay (and rocks spread around the area, but held away from the perimeter areas), that will be covered by 3" +crusher run, followed by 1" crusher, but we won't be stripping any more than the absolute least amount needed to get to subsoil, so as to be able to limit the necessary depth of the posts/footers where ever possible.

Our low areas run up to 42" of fill needed to get level, plus another 6"to get the inside floor above grade in a 30x45' building area, but that also means we need a minimum 2' wide surrounding bolster, set with a 3/1 slope, meaning that it needs to be 12' wide at the lower areas, estimated at 80-90 yards of gravel, not including the clay and rock and running about 3500$ minimum.

We thought that picking a building contractor and getting building would be the hardest part, but finding the right excavation contractor and plan has been much harder.

Thomas
No matter where you go; there you are...

 

[DJ54]

Completely forgot about the concrete washout.... That's what I used under my big building at my present location. I put it in in 1' lifts, and rolled with tractor, then with the dumptruck as I backed in for another lift. That was in '93 and no settling what so ever, and it is over 6' deep on the north end.

 

[mx842]

Another thing that works really good is old crushed concrete. Here they recycle old concrete, they haul it to a storage yard and run it through a crusher and it is a lot cheaper than regular crushed stone. I used it in my building and on one end I had to bring it up about 3 feet in places. I pushed it in to fill it up to about 8 inches of grade and run over it a time or two with the skid steer then watered it good and went back over it again a few times with the tractor and the next day it was like solid rock.

This stuff around here is over a hundred bucks a load cheaper than crushed stone and I think it is better for stuff like this than stone or sand. I hate sand for use as fill for a pad especially if it need more than 4 or 5". It will shift too much even when compacted and unless it is completely encased in concrete it will move over time. It also makes it easy for mice and other critters to dig under your pad and make tunnels for nice warm homes in the winter or cool ones in the summer.

 

[radioman]

I kinda agree with physassist- The key here is virgin or undisturbed soil. However taking a local virgin soil and add on to already virgin soil "should" raise the frost line higher so footings doesnt need to be deeper. (I am not saying it wuiill be less then 42 but the filled in area frost line is still 42") The problem is compaction so its simalar to undisurbed soil. You also need "time" to allow soil to settle in after filling and compaction for best setup.
Question is do you have the time like at least year or two to let rain and frost to settle out the dirt after filling in before building? I am sure you have the right idea to pull stumps and roots and any other organic materail before filling in, but you also will be disurbing the soil- by alot. a sheep foot roller or jumping jack should help here .

 

[George2615]

I used bank run as well to level off and fill the area where the pole barn went. After leveling I used a gas powered compactor to pack it down. Compacted it a little each day for about 3 days. 2 weeks later the floor was poured. After it set expansion joints were cut.

 

[Buck455]

Sounds good. I'll be looking into the crusher run and crushed concrete. I assume as you near the top of fill you'd want to make sure you keep the grain size low.....less than 1".

My plan right now is to take 1' off the top of of my highest point and set grade there....sloping the surrounding area away. That area is actually the end of my driveway, so I believe it's safe to assume no organics in that area...we'll see when I pull the roots though. The rest of the area is grass. I'll pull as little away as possible to get the vegetation out and go below the undisturbed surface 42". I have ordered posts extra long to account for being 4' low on grade at the far corner and 2' low along the adjacent sides to make sure I'm below frost line without any fill. So at the far corner, I'll be over 7' below finished grade. Once I have the skirts up, I'm going to start filling in about 6" lifts until I get to final grade. I plan on renting a jumping jack to do the compacting as I don't have anything heavier than my 3/4ton pickup to roll it with.

Does that all sound appropriate?

Beyond that, how do you guys feel about insulating and vapor barrier? Is insulation necessary or worthwile? Do I need and inch or two of sand over the vapor barrier or should I lay concrete directly on plastic?

Thanks again for all the advice.

 

[sdkubota]

Gumsho was exactly correct...a non topsoil, no organics soil is fine. Put it in 6" lifts and make sure it gets driven on good before adding another layer. Just by placing the soil, you will pretty much get your compaction coverage. The soil you place and compact will be noticable stronger than the surrounding soil. Use 8" or 6" of gravel at the top to aid in leveling for the concrete and add stability to the concrete floor base.

 

[mx842]

Sounds good. I'll be looking into the crusher run and crushed concrete. I assume as you near the top of fill you'd want to make sure you keep the grain size low.....less than 1".

My plan right now is to take 1' off the top of of my highest point and set grade there....sloping the surrounding area away. That area is actually the end of my driveway, so I believe it's safe to assume no organics in that area...we'll see when I pull the roots though. The rest of the area is grass. I'll pull as little away as possible to get the vegetation out and go below the undisturbed surface 42". I have ordered posts extra long to account for being 4' low on grade at the far corner and 2' low along the adjacent sides to make sure I'm below frost line without any fill. So at the far corner, I'll be over 7' below finished grade. Once I have the skirts up, I'm going to start filling in about 6" lifts until I get to final grade. I plan on renting a jumping jack to do the compacting as I don't have anything heavier than my 3/4ton pickup to roll it with.

Does that all sound appropriate?

Beyond that, how do you guys feel about insulating and vapor barrier? Is insulation necessary or worthwile? Do I need and inch or two of sand over the vapor barrier or should I lay concrete directly on plastic?

Thanks again for all the advice.

I'll probably get beat on for saying this but here goes. I think some folks put a little too much thought in as one would say 'soil compaction'. Yeah you want to have a good base under your floor but it's not really necessary to go overboard. Topsoil will pack just as hard as bank gravel and if it is kept dry you shouldn't have a problem with a floor poured right on top of a topsoil base under a normal work shop garage. You do want to make sure the soil is clean of roots and other organic material are removed but these things have a habit of working themselves to the top as you are moving the soil around so if you miss a few when taking out the root mat you will find most any remaining trash as you spread the dirt around. As they pop up you can pick them up and throw them off to the side.

In most cases when you have a sloping area where you want to place a building with the difference of 3 feet from one end to the other by the time you strip the root mat off which is normally somewhere around 6" and then cut the high end out and move it over to the lower end and smooth it out you are not going to need much fill at all. The beauty of pole barn construction you can wait to pour the floor once the building is up and the roof is on. By this time the dirt under the gravel you will put on will have settled well enough to pour your slab. You may have to remove a soft spot here or there where rain water didn't drain off but just cut out those spots and fill in with stone.

Keep in mind if you have a big difference between one end to another you can lower the high end more and by doing this you are going to create more fill to help level out the building pad. You will find more dirt than you need because you will need to cut a swale around this end so that you will have proper drainage away from your building. You will need to grade away from the building regardless weather the lot is sloped or flat so if you need fill material you may as well use what you have on site rather than paying 4 or 5 hundred bucks for a load of gravel just to use a fill if you don't have to. You also need to remember that if you build up the inside pad area 3' you will also need that much on the outside of the building to back fill with and this can take a lot of dirt as well but you can use the root mat and less desirable soil to do this with. Just another reason to lower the high end somewhat to help bring the whole building pad construction cost down and have a better overall building site.

Also you are going to grow dirt when you dig your post holes because you are going to back fill them with concrete and this dirt can be mixed in with what you have already spread out in the area. When you have a situation like you have and you move the dirt from one side to the other and mix in what you have left over from post holes and other things as you are working on inside the building site you will probably find you are not going to be far off from sub grade and a load or two of some type of gravel will be all you will need to be close enough for the time being and you will be glad you have a nice gravel layer to work on while you are working on the building. By the time you are ready to fine grade the area and get it to sub grade you will see that the gravel you placed on the dirt inside the building will be already packed hard from just the normal everyday walking and working on it. Just grade it so that the water can run off and not puddle and this too will help settle the soil and gravel. By getting it close but not too high when you first add stone to cover the moved around soil you hopefully wont have to do anything but add an inch or two of some type of gravel and dust mix like crusher run which is easy to move around to get it up to final sub grade. You shouldn't even have to run a compactor on it unless you need over 5 or 6" to bring it up the sub grade.

yes I would put 6 mil poly down before you lay out your rebar or wire. This will help keep moisture from wicking up through the concrete when it's damp outside, you will be glad you did. Yes pour the concrete right on top of the poly. It's okay to throw a little sand or gravel on the poly to hold it down while you lay out your wire.

As far as insulation I don't see any need to add insulation under your slab unless you will be installing pex in the floor for a floor radiant heating system. In my view that would be added expense that you would not see enough benefit from to justify doing so. I would however consider putting in a slab floor heating system if you plan on heating the building it would be money well spent and hard to go back and do after the floor is already poured, just a thought.

 

[sdkubota]

Here is where you are mistaken...topsoil may pack fine but is prone to swelling and shrinking with changes in moisture levels. Once a concrete floor is constructed the evaporation/transportation (capillary action) mechanism is blocked and moisture levels will increase below the concrete floor.

Footings can be placed on compacted fill without any problem. Having it all undisturbed would provide for uniform bearing but in most cases with a large light framed building it is not the down pressure that exerts the greatest pressure but the uplift (giant wing). A good compacted clay will work fine and in fact is capable of supporting greater forces than the undisturbed soil.