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Proctors on Granular Free Draining Soils

Proctors on Granular Free Draining Soils

(OP)
thread261-294727: Bleeding Effect during Proctor Testing

This is in response to the another thread that mentioned bleeding water while running free draining proctors, and I would like to re-open the discussion.

I manage a soils lab for a Geotechnial firm, and the majority of questions or challenges come from preforming compaction testing on structural/pit-run/free draining soils. I believe this happens because the way of traditional compaction is beginning to become obsolete for the current soil standards today. What I mean is, that ASTM D1557 Modified Proctor test was made for using soils in-which moisture affects its compaction to generate a moisture/density curve. These structural soils that are free draining now being used are causing problems with this standard as moisture does not affect the density as much as a native silty sand or fine grain soil would.

When running these free draining soils water will begin to leach out of the mold at higher water contents and at that particular point should be scrapped. You are compacting soil that is at varying moisture contents throughout the test as water is being removed with every blow of the hammer and therefore will not be the correct moisture when done. If you grease or seal the mold as some do that water will come to the surface making a muddy mess and can splash out of the mold causing the same water loss problems. Often times these soils present the first two or three dry points moving upward at a constant angle on the graph and then the wet point/points jump up in density to give the curve an exponential graph look, concave up. The curve will never drop as normal to create a typical wet side of the curve or a concave down parabolic graph we all know and love.

These soils I tend to recommend doing a maximum field density test having a contractor roll and roll and constantly testing to see its maximum effort, or to run ASTM D4253 Vibrating Table method for cohesionless soils. However, that standard is not available very often and ASTM does not require it, and until it does, I see D1557 continuing to be used rather than buying the new equipment.

When presenting these curves to Engineers it is always questioned and an explanation always follows.

How do you handle running free draining compaction testing? Does it work out for you? How do you explain the results of unnatural curves? Thanks.

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