Wes, Bruce,

I know that there are rammed earth dams and that highway sections are built on compacted fill -- why not a house?  Is it a function of the type and weight of the equipment that is used?

Very respectfully,
Larry

When I was younger, I worked on a Survey Crew. We performed a lot of subdivision work. I remember them taking about 20' of virgin soil off the top of a hill and moving it to the lower areas. We had piers of dirt so high we couldn't even reach the lath that we had pounded in a few months before. I told myself that I would never build a house in an area that was all fill. There are no guarantees that they did it(the compaction) right.
 
The last thing that anyone would want is their new hose settling into the 'abyss'.

There is a difference of course between compacted soil or organic matter and compacted gravel and sand.

There is absolutely no reason that it can't be done.  As you correctly point out, many things are built on sound, compacted fill (this means no organic matter).  The caveat is that it needs to be done correctly.  This means doing it in lifts appropriate with the compaction equipment, monitoring the moisture content (if your soil is too wet or too dry, it will NEVER compact correctly) and testing, testing and testing.  They have little nuclear density testing devices to do that instead of the old style Proctor sand cone test.

Another way to prepare a building site on fill is to consolidate (a fancy word for compact) the soil by putting 3, 4 or more meters of soil over the area and letting it sit for a while.  The weight of the overburden does the job.  The soil under JC's topsoil storage example was probably well consolidated, but I doubt that is why they did it.

Differential settlement is a problem you want to avoid.  This is a danger if you have a building that bears on different foundation types (i.e., spread footings under one part and piles under another part).  Buildings can usually withstand considerable settlement if it is uniform. 

Bruce

Another point to watch when building on fill is to make sure you start from a level.  I've seen houses built where the fill was simply poured onto a relatively steeply dipping slope to build up a ledge on which to set the house.  Didn't take long for the house to start moving downhill, riding a wave so to speak.  Excavate to level undisturbed soil first.

Monolithic slabs are a regional preference, I have successfully done many in Florida & Louisiana. Clean fill properly placed and compacted in 18" lifts to at least 95% density, I have fiiled as much as 7 feet using a monolithic pour on top and installed an in ground concrete swimming pool, with no problems.
Wouldn't hesitate at all to pour a monoloithic slab in Florida.
Can't speak for other areas like Wes in KY. its usually best to go with what is "normal" for the geographical location.
In Louisiana I would strongly consider a monolithic post-tensioned slab due to expansive clay and river silt.

The subject has swayed a bit.

Getting back to the subject at hand, I've seen and installed radiant heating in many finished concrete floors/slabs. They can be quite beautiful and low maintenance, as you would expect. Your ideas are not misplaced, just used more in areas that are forward thinking in design.

Depending on where you live, you may just have trouble finding a mason capable of producing what you want. Be sure you view their work, ask for and call their references before hiring anyone.

rykertest

A monolithic slab is the most inexpensive way to go and is used frequently in the southeast;
plumbing drains are in the slab but water distribution and electrical can be run from either underneath or overhead.
if you are in a northern climate you may want to consider a different method

Concrete floors that are stained or polished can be very appealing and beautiful when done correctly, and are definitely low maintenance. However you may find that after living and standing on them it is a bit harder on the body, especially the back, then you expected. I can attest to this, not from living in a house with a concrete floor but working as a machinist and standing on one for forty hours a week. My friends who built their house with concrete floors said they would probably overlay with wood flooring if they had to do it over again as well for the same reasons I have mentioned.

I am currently living in a house built by my dad in Tennessee, it is a three story house (2floors+basement) build on a thickened edge monoslab, 12" under the walls and 4" under the floor. The monoslab is about 6' below grade on the back side and 8' below grade on the front. It was installed on excavated soil, not fill, was chocked full of rebar, and the monoslab was tied into the block wall using rebar. The outside was coated in two coats of thoro-seal all the way from the top of the blocks to the bottom of the monoslab, then foam boards, and finally backfilled with gravel. The blocks are exposed with no coating on the inside. I have never seen any evidence of dampness or water anywhere. All the blocks and the slab have that white look to them, where you can tell they have been dry for a long time. We don't even use a dehumidifier. The house is 25 years old, and only has about 3 localized hairline cracks in the whole slab.

I have seen brand new homes built using the "typical footer/blocks/slab" by experienced contractors with dampness issues and serious settlement problems. The monoslab is one of the best foundation styles IF YOU ARE WILLING TO MAKE SURE IT IS DONE RIGHT! If your aren't willing to do your homework and watch your contractor like a hawk, pick something else.

Check out this website. These people did some interesting things with concrete floors. http://www.ourcoolhouse.com

probably the first step is to talk to your building department, then conctere contractors then a civil engineer and you might need a soils report. you will probably get a lot of different answere just like the posted suggestions... some high clay content soil will expand and contract with varing moisture content and can crack floors.I have seen 18 inch bored holes filled with rebar and concrete several feet deep supporting the foundation then a non supporting footing grade beam .. I looks like a buried freeway bridge. some areas have the soil already mapped and others will require a site inspection, I came in on an energy efficient home after it was started. the floor was planned about 3 ft above natural grade. the foundation walls were insulated with 4 inches of foam on the inside, then soil fill compacted then gravel, 4 inches of foam more gravel to sub grade, then the 6 x 6 10 ga 10 ga mesh with the radiant heating-cooling tubes and the final concrete floor. the house is about 2 years old and the home owner was very happy with the results.