Another criteria is "structural fill" such as beneath footings or heavily loaded floor slabs where I would use Modified Proctor (granular soils) - most highway subgrade and fills is standard Proctor until you reach pavement structure - subbase and base where Modified is typically used - tells the Contractor you are "really" serious.
is proctor test only applied on fill material ? or may it applied on natural ground too ?
i mean it do usually comparison between field density and lab density for natural ground to check the compacted .
If you employ any compaction, whether natural ground or fill material, you must have a means of comparison, so a laboratory moisture-density relationship (Proctor) is necessary for each different material to be compacted.
I've never been one to specify a compaction for natural ground - only that the natural ground be "undisturbed" (footings, etc.) For parking areas and roads we would proofroll the natural ground to locate any soft spots; if found they would be subexcavated and then backfilled. Supposedly, if the natural ground is the material on which the designer designed, he was satisfied that the natural ground was suitable for his purposes; hence, undisturbed / proofrolled. I have seen specs and known others that differ, though.
many specs call out to scarify and recompact the cut or stripped subgrade surface. this would be done to the compaction criteria specified. i typically disregard this and only proofroll the subgrade and correct as needed (as is also usually specified). one could perform compaction testing on recompacted cut, but i don't see the benefit except achieving some sort of bureaucratic pursuit.
Per Big H's comments, I have had a density tests done on natural ground from which material will be taken for a compacted structural fill, generally a clay. The purpose is to be able to justify a percent compaction of the fill equal or better than what exists naturally in "acceptable' conditions. This first came about when we were raising hell with a contractor not getting the specified compaction of a silty clay fill. Contractor asked our tech to "test" the natural ground where we had OK'd the use of footings. That was a surprise to us and made sense I guess. Since then I have used this "check" from time to time. Most of those checks of "suitable ground" showed percentage of lab Modified Proctor as low as 83 percent and still acceptable for footings at maybe 3,000 psf and for sure many a parking lot.. After that, I have leaned more to using the unconfined compression test as the deciding testing acceptance when compaction specs are difficult to meet. We also later learned that 95 percent of the lab density might result is a density which, later results in a significant problem with expansion of some clays. That 90 or 95 percent number is not a magic solution to getting a good job. It can be the cause of great difficulty if not used wisely.
