I'll disagree to a certain extent, I worked in the excavation field as an operator for a number of years in my construction career, from residential subdivisions to high rises in NYC.
For a pole barn with a known material, even like run of bank gravel or quarry material like crusher run, using 12" lifts and a heavy vibratory roller is fine, (make sure to clear and grade the site of top soil first) + with the lead time he mentioned prior to placing a slab, it should be no problem there, 1 year to settle. Unless there is underlying geological issues that are unforseen under the site, it should be fine. A known material with the right moisture content will compact at least 95% or better. I've seen higher readings than that with some materials and have also done the key ways of earthen dams that required 100% compaction myself, with a D5 cat and tow behind vibratory roller, using suitable fill.
On more complex jobs, as well as certain local municipalities, say for example; city of ny dept of buildings, every fill lift is tested, and recorded by an independent testing lab, and signed off by a licensed P.E. on a report TR-1 form, on every job a permit is granted for, or you will be in violation, that could easily mean removal of the work. NYC requires controlled inspections throughout the various stages of construction while constructing any building, highway or utility work. I cannot imagine doing work without testing in that area, you would have new buildings and highways failing left and right if left to contractors, even self certifications are a problem there, this kind of keeps suppliers and contractors in check and protects owners.
I'll agree that it's not a necessary thing when you have known good materials and qualified people doing the work, I've done plenty as an operator myself, with no testing needed.
I'd have concrete test cylinders taken if I was doing any structural concrete, even a home foundation, same with fill compaction if it was anything of quantity, say just a few lifts in a few locations, that Troxler Nuclear Density Meter sure does a nice job, density, compaction and moisture, couple of tests can't be that much, and if the material is uniform, most likely it's good from that source, though optimum moisture does need to be monitored.
When doing certain type projects under different circumstances, and something fails, where is the back up, documentation or supporting test reports if no tests are done at the time the work was performed, say like concrete, naaww no need to take test cylinders, the wall or pier fails under a load, and there is no documentation, leaves the contractor or owner wide open for a claim. Well you get into forensics, can do a windsor probe for concrete after the fact, but soil work may be hidden or inaccessible.
On private work, you can obviously do as you like within the applicable codes, but if you are spending a serious amount of money, the costs associated with independent, controlled testing are trivial if a claim ever arises from faulty or defective materials. Not trying to lecture or argue or be a thorn in anyones side here, my intent is to help or share knowledge, (I get carried away sometimes especially when home on doctors orders like today) but a good testing firm, with good field inspectors can be a requirement, or just money well spent to avoid bad situations. I've had testing lab inspectors root out defective or missing reinforcing in a form that I missed,(have photos of this too) same inspector also stopped the contractor and made them correct the work in the middle of the pour or have it rejected and re-done at their cost, not all are as you suggest, I like the ones that don't take crap from contractors, had that structural component failed, it could have caused a building to collapse and opened the door to for people like myself to be liable, simply put that inspector taking test cylinders and inspecting the form, and comparing the work to the approved shop drawings, did his job correctly.
Now look at it this way, say contractor B on this job is awarded the contract at $1000 dollar savings to the owner, to provide the clay/gravel/loam or what have you, a type of unknown fill, say it's spoil off another job or unsuitable, or who knows, the owner may not be aware of it, contractor places and compacts the material, it looks good but is not sound, a year later slab is placed, it settles or fails sometime after. Now what, you have a serious claim that becomes a mess in short order, yeah you can determine that the fill is unsuitable, but now the contractor is gone, you paid him, he's out of business or will fight you. You still have to pay for dispute resolution if it goes to litigation, have to pay to correct and re-do all the defective work, vs., whoa buddy, (at the time it's being done) this fill is unsuitable, take it out, reject now before the rest happens as mentioned above, pay now or pay a lot more later.
I see these kind of thigs happen all the time, concrete wall fails, blame game.... yup was the excavtors fault, he backfilled too close too soon, well did anyone inspect the form for reinforcing, did anyone test the mix with test cylinders, and what were the breaks, was it reinforced correctly, did someone authorize the excavator to backfill too soon or was the mix design just defective ??? Those testing outfits are there to verify that things are what they are supposed to be and provide the owner with documentation stating such.
I hate seeing an owner get taken, yet it happens all the time, not everyone is savvy to sound construction practice, management etc., they trust the contractors to provide a good faith effort to adhere to methods that foster good workmanship, yet we all know there are those contractors who don't do work to industry standards and leave owners hanging, due to poor qualifications, education, ability or plain ignorance, that is exactly why you have construction managers to represent owners and their interests, as well as testing labs too, they do serve a purpose.
