Density Testing using modified Proctor when standard is required!

[jharm]

I have a situation. I have been testing for 2-days using a VTM-12 (Virginia Test Method) One Point Proctor values of 104.7 lb/cu.ft @19.2 OMC. The VTM-12 test uses Standard effort.

For 2 days I have passed compaction in a green area requiring 85% of Standard Proctor. My lab tech mistakenly ran a modified Proctor yielding values of 115.3 lb/cu. ft @ 14.9% OMC. Obviously, the previous tests no longer meet the 85% compaction required.

I will have him rerun the test, but in the meantime, can anyone give a general %-comp equivalency for 85% and 95% of Standard Proctor? Soil is a sandy CL with negligable gravel.

TIA

 

[DarthSoilsGuy]

you're one-point testing is much more accurate than any rule of thumb will be. What was your one-point?

also, if I specify 85% for a yard area, i'm more or less telling the grader to "track it in" since they won't be able to build on it later. i can't see anything bad happening in the future if it were 82's and not 85+'s, unless it should have been specified higher in the first place.

i would double check to see if there might be a higher utility backfill soil specification that may be crossing your green area. They may have to put in utilities and not dig all the way through the yard fill to existing materials.

on another note, i have seen some retaining wall engineers specify 95% Std or 92% Mod. i believe their rational is to keep the design as general as possible to work with site specs thus keeping the phone calls down. In my experience, relation b/n the (Mod Proc/Std Proc) is greater proportionally for clays than silts, or silts than sands, and finally sands than gravels. so, i couldn't give you a rule of thumb.

 

[jharm]

Thanks. The one-point yielded a 104.7 @ 19.2% Gravel is negligable.

 

[DarthSoilsGuy]

i followed that the one-point yielded 104.7 @ 19.2. i was asking what the point was itself that got you to the maximum dry density.

You are not saying your one-point and your maximum dry density are the same point?

If that were the case, you would need to dry back the sample and run your one-point again. One-points must be a little dry (3%-5% is good) of optimum moisture content to give meaningful results to extrapolate a maximum dry density.

 

[jharm]

I'm sorry. Misunderstood the ? WD = 120.9; DD(calculated) = 102.2; MC = 18.3%

Thx

 

[DarthSoilsGuy]

my artistic interpretation gives a 104@20 so i don't see any problems there as long as the methods are right. it is a little closer to the saturation lines than i prefer myself.

the 1st thing i always would check when reviewing density testing was if the one-pt looked legit. just a habit of mine.

I think you'll be fine. Let us know if you get any surprises.

-Cheers,
dsg

 

[fattdad]

the difference between standard and modified Proctor is about 5 percent. 85 percent modified would be about 90 percent standard, etc.

hope this helps. for what it's worth, other very important points have already been addressed.

f-d

¡papá gordo ain’t no madre flaca!

 

[civilperson]

I find on silty clays and clayey silts that Sandard Poctor is 8-9% lower wet density at the same moisture of a Modified Proctor.