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Oversize Correction for Modified Proctor (D1557)

Oversize Correction for Modified Proctor (D1557)

(OP)
Does anyone know how to come up with the moisture content for use in calculating the oversize correction for proctor tests?

I think the idea is that larger gravel has less surface and holds less water. Therefore, the overall water content of the soil in the field will be less than the split portion tested in the lab. I'm just not sure how to figure out what that value is specifically. When the soil has up to 30% oversize, this number can make a big difference.

Bonus points to explain why the portion passing a #200 is relevant. I don't get why the standard even bothers saying to record it.

Cheers.

RE: Oversize Correction for Modified Proctor (D1557)

See ASTM D4718 "Standard Practice for Correction of Unit Weight and Water Content for Soils Containing Oversize Particles"

RE: Oversize Correction for Modified Proctor (D1557)

Let's say you have some fine to coarse sandy gravel with silt. You process out the plus 3/4 and run a proctor. You have 30 percent oversize material. From the minus 3/4 you get 125 pcf at 12 percent moisture. (I'm just pulling this example out of my head.) Well the rock that you removed (if it was present) would add 165 pcf if it was floating about the minus 3/4 material. So for any given cubic foot of material compacted to 100 percent relative compaction, you'd have 70 percent at 125 pcf dry density and 30 percent at 165 pcf dry density. That'd give you a maximum dry density of 137 pcf. That just isn't much water inside a plus 3/4. So, your optimum moisture content would go to 8 or 9 percent. I'd have to look at the equations in the ASTM for that, as there may be some assumptions for SSD moisture. On first principals, though it all makes sense to me. . .

f-d

¡papá gordo ain’t no madre flaca!

RE: Oversize Correction for Modified Proctor (D1557)

(OP)
Perhaps my question was not clear. I simply want to know how to figure the oversize moisture content to use in the equation. ASTM D4718 says to do just what you said fattdad, a weighted average. I.e. (percent passing 3/4"*moisture of passing 3/4")+(percent oversize*oversize moisture). But what is the oversize moisture?

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