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Relationship between Relative Density and Standard (or Modified) Proctor

Relationship between Relative Density and Standard (or Modified) Proctor

Given that cohesionless soils (less than 15% fines or so) should be done by means of relative density - but this isn't usually the case as almost all highway specs I have seen still call for Proctor (standard or modified) for compaction control - I was wondering if anyone out there has actually done any comparisons of the 100% MDD (std or mod) vs Relative Density - say, then, too, what 95% of MDD would yield for RD? If you have and are willing to share, I would appreciate it - am putting together a presentation to our lads (and lasses) on site about compaction.

Too, has anyone ever determined, say for a well graded sand and gravel (natural or crushed) what difference in deformation modulus would be expected compared to various percentages of MDD. Many times we get this fixation on 95% and then go bonkers if we get a 93% - so what is the expected difference in settlement or support behaviour between 93 and 95%?

Appreciate any information that one has . . . - first hand would be best. cheers

RE: Relationship between Relative Density and Standard (or Modified) Proctor

BigH....we tried something like that about 35 years ago here in the land of the coastal plains. Our sands can be relatively clean but they are poor graded (SP, SP-SM,SP-SC). We were the only lab in the area with a vibration table to do RD (that has always been one of the impediments to using RD vs. Proctor). We tried a few correlations but didn't get very far with it. Because of the limitations with equipment and training (there's more diligence required to do RD than Proctor!), we did what everyone else did....we lived with the occasional quirky Proctor curve. For the most part, we could develop good Proctor curves but occasionally we would get a "double hump" curve or one so flat that everything would either pass or in-between.

Wish I had the data you seek...but not available. You might check with John Davidson at the University of Florida. He has been around for quite some time and might have done something (he was there quite a while before Schmertmann left)....haven't seen a paper on it though.

Good luck.

RE: Relationship between Relative Density and Standard (or Modified) Proctor

In my case the relative density method was used mainly for Vibroflotation jobs for buildings.
There I think the 70 percent figure maybe came from Ralph Pecks's work and we used that as an acceptable degree of compaction. For other building jobs I also think we reverted to relative density, when Proctor type criteria looked goofy, to accept a job that didn't meet that criteria (95%, etc). I don't think we tried to relate the two as you ask.

One factor that we probably considered for some materials was the breakdown of some materials in the Proctor test as compared to the vibration method for max density for RD.

RE: Relationship between Relative Density and Standard (or Modified) Proctor

Thanks Ron and Oldest Guy - - I fully understand that not many have the vibrating table and in looking at ASTM's method of doing the maximum test, I can see why almost all would back away. BS 1377-4 is much simpler in the reading and understanding that the verbose ASTM (2 pages vs 14) - they actually use a impact vibrating hammer as one does with Roller Compacted Concrete - but breakdown in this could be evident too. I've see one example from a ppt that I got off the internet - but can't remember the URL that shows that testing on Fort Worth - 28 filter sands - gave 70% RD = 1 point Proctor and 50% RD = 95% of the 1 point Proctor.

Our sands are basically 90% finer than 2mm for filter - compact really well with a 1-tonne tag-along . . . I will be doing a standard Proctor to compare against the RD values we are getting which are consistent.

Appreciate the thought.

RE: Relationship between Relative Density and Standard (or Modified) Proctor

BigH....I assume you are using the standard proctor (vs. modified) to limit the compaction not increase it, since this is a filter application?

RE: Relationship between Relative Density and Standard (or Modified) Proctor

Ron - yes, standard Proctor. But for my purpose I'd take any correlations that might be out there - as I am putting together a presentation of our lads and wanted to show them, even if for highway base or subbase, what might be expected if RD was used rather than Proctor.

RE: Relationship between Relative Density and Standard (or Modified) Proctor

refer to Lee and Singh, Journal of the Soil Mechanics and Foundations Division, ASCE, V. 97, No. 3, 1971.

In summary, RC=80 + 0.2Dr

The implication of this equation is that at 0 percent relative density, you have 80 percent relative compaction.

Please note that there is no pracical meaning to 0% relative compaction, but there is meaning to 0% relative density.

So, 5 percent relative compaction has a 25 percent effect on the relative density.

Now, I'm sure that the work of Lee and Singh is based on Standard Proctor, which confuses me as Modified proctor maximum dry density is typically 5 or so percent greater than Standard Proctor.

Hope this helps.


¡papá gordo ain’t no madre flaca!

RE: Relationship between Relative Density and Standard (or Modified) Proctor

fattdad - it is good to see someone else still remembers papers from the 60s and 70s! Unfortunately, almost all my references have been in deep storage since 1995 when I took off for Asia . . . and thanks!

RE: Relationship between Relative Density and Standard (or Modified) Proctor

Maybe 0% relative compaction means a porosity of 1?

Don't let your lads over-compact the filter! It's easy for a bored operator to make several extra (too many) passes while waiting for the next truckload of filter material. In his later years, Peck told us that 70% RD was pushing the upper limit of density, because of crushing -> loss of vertical permeability (more than horizontal permeability), stiffness, and cracking potential. Consider a test fill (lift thickness, roller passes, wetting yes/no) and a procedure spec based on that, with occasional record tests. We've done that on some fairly large filters for dam rehab.


RE: Relationship between Relative Density and Standard (or Modified) Proctor

Yes - that is the one . . . Thanks BigHarvey! and thanks, too, to David!

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