subbase fill for pole barn slab

[PhysAssist]

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.

As to insulating with vapor barrier or not, having worked in a heated building with uninsulated concrete floors, unheated building with insulated (but no vapor barrier), and an unheated building with an insulated floor with vapor barrier- having the floor insulated and dry makes working so much more comfortable that I never even considered not having the floor insulated and dry when we planned our soon-to-be-built building...

While I'd love to have a radiant heated floor, we can't afford tp put one in, and while this probably should be a no-brainer for anyone living in the rust belt, the dry insulated floor is next best....

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

 

[mx842]

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.

In a perfect world, yes I will agree that topsoil is not the best example of good base material for a building pad. To be clear, when I stated top soil I was not referring to the top most part of the soil where the root mat lives. That should be removed from the building pad altogether and that layer could be anywhere from 6" to 18" or more depending on the type and condition of the soil from one place to another. Heavily wooded areas the root mat will be deeper than bear or grassy type landscapes. What I referred to as topsoil was the layer under the root line that is somewhere in-between topsoil and the more desirable soil used to build things on. This layer is perfectly okay to build on if mixed well and graded so that it drains well. Have you ever heard of the term soil cement?

There are a lot of secondary as well as super highways that are build on road beds made of nothing more than removing the root layer of soil then preparing and stabilizing the less than desirable type soils that would cost to much to replace because of the lack of proper road building material close by.

Prepared soils; soil improvement which is nothing more than mixing the different soil types together and compacted. Soil stabilization goes a step further in adding in a hydraulic binder that is scarified and then run over with a machine that tills the soil finely and as this layer is mixed all together, lime, powdered cement or other hydraulic binders along with the proper amount of water is added to the mix leaving a smooth layer ready to be rolled to compact and seal the surface. Then a layer of gravel, surface treatment, concrete or asphalt is placed on top of this leaving a reliable road for travel.

What we are talking about here is a pole barn not a super highway there is little if any transportation involved here that a good 4" layer of 3500 lb concrete mix cannot handle regardless of what is under it.. Once the concrete is placed on top of the base material it will seal it off and if proper grading is done to remove runoff then excess moisture will be kept to a minimum so shrink swell should not be a factor with this type construction. Shrink swell soil problems are more related to crappy clay type soils than it is to the top most layers which usually have more sandy content. Shrink swell soils effect foundations more so than concrete pads because of the great amount of area that the movement is distributed to through out the floor.

 

[sdkubota]

I deal in facts using science and 20+ years experience as a registered professional engineer.

 

[mx842]

I deal in facts using science and 20+ years experience as a registered professional engineer.

Good for you sir! I'm no engineer nor do I have any fancy pedigree's. Facts and science sometimes has a way of creating heated pizzing matches on forums like these so I guess we'll have to just agree to disagree on this one because there usually will be no winners in discussions like this. All I will say is that my 40+ years experience of actually being out in the field building subdivisions, roads, Apartment complex building sites and site work on hundreds of other building projects sometimes what happens out in the real world does not match up with what goes on around a drawing table in some engineering firm down town so I will leave it at that.

 

[PoleBarnGuru]

Many sites can be graded with a skid steer (a.k.a. Bobcat) or backhoe. Some cases will require heavy equipment to properly grade site to allow water to drain away from building. If a professional is engaged for site grading, make certain finished grade prepared is adequate before making final payment. In far too many cases flat sites which are out of level have been experienced by disappointed owners.

At a minimum, site preparation includes:

Remove all sod and vegetation.

For ideal site preparation, remove topsoil and stockpile for later use in finish grading. In frost prone areas, remove any clays or silty soil from within the future building f��ootprint.

Replace subsoil removed from around building with granulated fill to help drain subsurface water from building.

Distribute all fill, large debris free (no pit run), uniformly around site in layers no deeper than six inches.

Compact each layer to a minimum 90% of a Modified Proctor Density before next layer is added. Usually, adequate compaction takes more than driving over fill with a dump truck, or earth moving equipment.

When any building portion sits on fill, rest columns, as well as any concrete encasement, on or in undisturbed soil. In many cases, building inspectors will require a soils engineer to confirm compaction adequacy on filled sites. Soils engineers can be expensive, but are even more costly when called in to do analysis after the fact.

Follow me at: http://www.hansenpolebuildings.com/blog

 

[jimgerken]

I prefer a mix of subsoil and crushed rock. It seems from my experience that the combination of rock and soil packs way tighter than either alone. When doing my own pad, I had the luxury of also having a gravel driveway to rip out that was 1000 feet away, so I ripped it out and loaded it over to the building pad site. The action of scraping it up and hauling it over and spreading it onto the building pad area really mixed the rock and soil together. It packed so well that it was very difficult to hand (shovel) dig into later and even a pick was too much work. Each day I'd bring over as much as I could haul with the loader, driving over the area with the tractor with full bucket, then backing up and spreading the bucket load, driving over again, backdragging, etc. Then after most of a day of this, a layer of a few inches had been deposited, I put the hose sprinkler on the whole area and let it run for several hours till bedtime. In the morning it was clear where the low spots were, so those areas were filled first, then an entire coarse was added again, and water sprinkled, etc. I brought one side up three feet this way, which took weeks of me working alone with my compact tractor. The action of adding water, if you can tolerate the mud or work it into the schedule properly, is incredibly powerful at causing natural re-arrangement of the fines that make the voids fill properly.
If I had to, I'd buy crushed rock, like 2 inch minus size stuff, to blend in with the subsoil and spread to pack. There must be huge regional differences in the cost of crushed rock because one guy in a previous post said 100 yards deliverd would cost him $2000-$3000. In my area, that would be $1000. I had 48 yards delivered a month ago and the bill total was about $500.
I have great confidence in the bearing capacity of this method, as I later had to dig into it in certain areas, and it is incredibly well packed together. I'd much rather dig into virgin subsoil than into this packed pad.
BTW, no inspection or standards trying to be met here, it is an Ag pole building, by definition.

 

[PhysAssist]

Duplicate post deleted...

 

[PhysAssist]

Quote:

"When any building portion sits on fill, rest columns, as well as any concrete encasement, on or in undisturbed soil. In many cases, building inspectors will require a soils engineer to confirm compaction adequacy on filled sites...."

Please explain what you mean here in the first sentence....

Do you build in New York state?

Your site is pretty complete and comprehensive!

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