Proctor Cuve on Granular Soils

[DirtLabNut]

I have been doing all the research I can on this topic, and I have gotten mixed results. A traditional nice parabolic curve with at least 4 points to find your OMC and MDD on higher fines content soils is great. Works every time. I understand that soils with low fines content should be run by RD, vibrating table. We do not have a table or can find any other labs in the area that do, so we run lower fines soils by Proctor as well D1557.

I have found that the graph never falls or drops on the wet side of the curve, but only goes higher until it reaches the z line and we stop. The last/wet point often is very high in density and does not follow the angle or trend that the curve was going with the drier points. That last point is sometimes a mud puddle. Our Geotechs always want a parabolic curve to submit in reports or to inspectors.

Would it be wrong to draw your curve following the angle of the first two or three points, and fall the curve just before, or on the z line? You would bypass the last wet/muddy point that is abnormally high, to fall the curve where your traditional line of optimum tends to be near the z line. This means that you are extrapolating your proctor curve based on the theory of the test without obtaining a falling wet point. Is this something that is acceptable or should we leave these free draining curves facing concave up without a proper parabola? See attach. Thank you.

 

[Ron]

DLN.....I'm not sure why your curve is off so much; however, with the unit weights your are getting and considering that you say the material has few fines, I would bet that your specific gravity is actually higher than 2.65. Having said that, you curve still looks whacky! Have you run this several times? I've run hundreds of Proctors on granular materials in coastal plains soils. The method works fine, including having a curve section parallel to the ZAV curve.

Check your procedure. Granular materials will generally produce a flatter curve than materials with some fines; however, there is almost always a defined curve in the classic sense. Occasionally we run into a "double hump" curve; however, that is usually on lower unit weight, poorly graded fine sands.

Run your test again and post your results, including the data.

 

[killswitchengage]

i have seen this before ! if i am not wrong it has to do with the material it self . You see some material when crushed will have higher specific gravity to it , think porous grains : water will enter the pores and substantial crushing will demand even more water to attain higher densities. This idea was introduced to us from an expert but i have forgotten the solution to it
i believe you should weigh the material after crushing not before .

 

[DirtLabNut]

Ron- we run into this constantly with low fines material. This is why ASTM has the relative density standard, but very little labs do this. They still use Proctor. The last wonky point will be a mud puddle, standing water/pumping. We seal the bottom of our mold to prevent seepage. These are type 17 pit run, poorly graded sand with gravel. Rarely do I see this type of material show a falling or typical proctor curve. I see the very shallow curving graphs with lower density clean sands. I have seen the double hump as well. Whenever I see the traditional graph with these soils, I look at it suspect. Moisture, given these soils free draining abilities does not affect the density of these soils as a SM or ML soil would. It seems to get to a point where the soil is saturated/standing water and when you weigh the sample,excess water is weighed and weighs high. Even though we can see pumping and saturation, the scale reads it as an abnormal gain in density.

Killswitchengage-If you could dig into the solution that you found that would be great! This is a topic that has been a thorn in my side as there are many differing opinions. Thanks to all.

 

[Ron]

DLN...what is the actual specific gravity of the material?

 

[oldestguy]

Have you ever taken each point material and run a gradation test on it? Do you re-use material from dryer points? I'd bet a few bucks your pounding into that mold results in a different gradation by breaking some particles to a finer situation. this is a common reason why at times the poor contractor can't come up with the same densities as that Proctor curve and the inspector rejects the work.