Compaction Perm

[caddyr2]

I have a simple question that I hope someone could answer. What method do you use to compact the material in the mold to acheive 95%? Obviously you need a specific amount of soil in the constant mold volume to produce a density. I calculate the amount of soil needed and place it in three lifts in general accordance with ASTM D698 although it takes about half the blows needed per the ASTM. Some times the amount of blows is too much and the soil is below the lip so over-compacted. Sometimes the blows are too little and the soil is above the lip so under-compacted. Does anyone out there have a better way at getting the density correct? Right now it appears to be trial and error and my lab tech compacting the soil is getting frusterated.

 

[singingk]

Your right, it's just try and error, and sometimes it's a challenge for lab tech's patience to match such requirements (for example to prepare a sample for direct shear tests). But with your approach (given soil mass and moisture content) I think it should not take more than five trials to find the right number of blows to get 95%.
There have been more general Information about such problems in a very funny thread here, I think last month.

 

[singingk]

See: 95 modified proctor posted by Lozano in earthwork/grading engineering in February

 

[wannabeSE]

Caddyr2,
My only experience comes from the Soils Lab class that I was required to take for a CE degree. The class performed a standard Proctor Compaction test. The soil is compacted so that it is above the top of the mold. Then, the excess soil is removed by trimming with a straight edge before weighing.

A good book for the fundementals is Soil Mechanics Laboratory Manual by Braja Das. An understanding of the basics of soil mechanics is required. Das also wrote a good text on soil mechanics, Principles of Geotechnical Engineering.

 

[caddyr2]

wannabeEIT: That wouldn't work in this case because I need a specific amount of soil in the mold and if I compact it as a standard Proctor I will never acheive my 95% compaction. The 25 blows per layer will densify it much further than the 8-12 that I currently need. I have come to the conclusion that I will just have to run this as a trial and error. Not a problem, I was just looking for an easier way. Thanks for the help

 

[geonebular]

What we do in our lab when we need to prepare a sample to 95% of the max. dry density (mostly for triaxial samples) is to calculate the mass of the soil needed per inch of the mold when compacted to 95%. Then place that amount of soil in the mold and compact by pressing on the soil with a proctor hammer removed from the sleeve (not dropping it), at regular intervals we measure from the top of the mold lip down to the top of the soil at several points and stop compaction once that mass is one inch in thickness, after scratching the surface to help bond the next lift, we repeat this until we have our full sample. For our triaxial samples we end up with (6) 1-inch lifts. I don't know of an ASTM detailing this procedure but we have fairly high confidence in our test results of samples prepared this way.

 

[fattdad]

Just a note on compacted permeability. Although you are seeking 95 percent compaction, the resulting permeability can vary by an order of magnitued based on the compaction moisture content. Mitchell, Hooper and Campanella (ASCE, SM4, July 1965 - and in particular Figure 6) show that remolded permeability is dramatically lower when compacted on the wet side of the LOO (line of optimums). (Bear in mind that the optimum moisture content to acheive 95 percent compaction is greater than the line of optimums to acheive 100 percent compaction.) For the case that you are seeking confirmation that a clay sample will be suited for a landfill liner or a pond liner, this knowledge can have a dramatic affect. Typically if you prepare the sample at 90 percent saturation (or greater), you will be in the appropriate range.

It does take trial and error to get the proper amount of dirt into the mold however. . .

f-d

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