Could Standard Penetration Test the relative compaction of the backfilling 2

[TAZKERAH]

Could SPT (Standard Penetration Test) be used to determine the relative compaction of the backfilling in-place for cohesionless soils? and Why?
If yes/ on which basis? and what are the limitations?

 

[MTNClimber]

Sounds like an academic question.

 

[jdonville]

There are easier field tests for use when placing backfill. To my mind, accurately evaluating existing backfill would require sampling, determination of in-place density and then recompacting the sampled soils in a lab to determine what the optimal density is.

I am sure there are papers out there that have looked at this problem.

 

[darthsoilsguy2]

It definitely can be used as an indicator of general compaction, however assigning a number will be subject to debate without doing some testing on a representative sample of known density. Definitely have used it in forensic investigations where compacted fills had been specified and were not provided.

 

[oldestguy]

I have a standing question. Why is it we will accept some reasonable blow count for footing support with no relative density testing when we insist on a high degree of relative compaction with tests that likely would result in a much higher blow count if a drill rig was on hand? I recall a K Mart store site earth moving job where SPT was done for he building as well as parking lot grading work . No field density tests. After many years of use, the parking lot behaved perfectly. It took some convincing the developer it would work and of course it did. Who invented that magic term of "percent compaction" and put any numbers to it anyhow?

Ya I know it was Poctor mimicking a herd of sheep (that's how come the roller got named that).

 

[MTNClimber]

OG - What do you think the standard degree of relative compaction should be?

If the fill material is good, its not hard to achieve 95% of SPD or MPD. If the owner and contractor want to save money and use less desirable fill, then that's on them. Deep fills do experience some amount of settlement. Why not try to reduce it with some effort? Geotechs take on millions of dollars of liability with a relatively very small fee. I haven't been involved in a claim regarding unexpected settlement using what my mentors have taught me. Why change now?

 

[oldestguy]

Run a test on natural ground considered to be OK for a reasonable bearing value. My experience shows it around 85% of standard Proctor generally.

Hey, it isn't a simple test procedure with "no sweat" problems. Take an extreme case at the St. Lawrence Seaway job some 70 years ago. The earth there was a very dense glacial til. Perhaps there was a break-down of coarser particles in the lab Proctor tests, maybe a bad stone correction number. I can't recall all the details, but my boss (a former Corps of Enineer)then was hired by the earthwork contractor to help him with meeting the Corps of Engineer's spec. Apparently it was not possible to meet the spec. with all sorts of effort. It got so heated a problem for the contractor that he committed suicide, even with the best specialist soil engineer helping him. Now that fussyness is really not needed on any job.

 

[MTNClimber]

Hmmm, interesting. I remember getting something around high 70's to low 80's of MPD on loosely placed clean sand and gravel, prior to any compaction.

There are special cases where common sense should prevail when compaction test results are "low" and the contractor is doing everything in their power to do the work correctly. It's certainty not worth causing delays on the project. I'd guess and hope that there were other contributing factors to that person's decision to take his life.

 

[EireChch]

OG - I have raised this question many times. Most natural ground is well below 95% and if we had to put a pavement / foundation on it we just account for the exiting strength. However if we have to raise the ground by 1m, we need a big earthworks specification, 3rd party testing and verification, a sign off report etc.

While in reality, if you use decent material and give it a few runs with the right compaction equipment you get a material much better than the existing. A good site engineer is required too.

I suppose the issue is liability and accountability. Everyone wants to defer responsibility.