ASTM D422 Hydrometer Test vs Sieve Analysis
ASTM D422 Hydrometer Test vs Sieve Analysis
(OP)
Hello all,
I'm working on a hydrometer test for our small company, but we just started doing these so I'm spending some time reading into the theory and analyzing our results. Technically ASTM D422 has been withdrawn; I've read some studies showing that the estimated particle sizes from the hydrometer portion of the test can be underestimated by up to two orders of magnitude due to the assumption of Stokes Law of falling spheres vs the disk or other shapes of real clay particles. This might be what we're running into but it seems unlikely because it's our first test and the distributions measured from the sieve analysis portion contradict results from the hydrometer portion. That is, the hydrometer portion is measuring all of the soil that passes the #10 sieve, which is estimated by percent suspended (calculated from specific gravity of the fluid+floating soils) and the estimated maximum particle size still in suspension (from Stokes Law). That same soil is later washed, dried, and measured again via a sieve analysis. The sieves are showing only 12% passing a #200, while the hydrometer analysis indicates 42% suspended after 2 minutes (so a particle size of about 0.037mm, about half of the .074mm of a #200 sieve).
Obviously these can't both be true, but we've triple checked the equations and they seem to be right. Is this a common problem with this test or is there something likely wrong with the calcs (spreadsheet attached)? I've double checked the measurements with this material and they are right. Also, is there a better place to ask questions about test-specific calculations than this forum? I've been looking around and can't find anything for that.
Thanks,
I'm working on a hydrometer test for our small company, but we just started doing these so I'm spending some time reading into the theory and analyzing our results. Technically ASTM D422 has been withdrawn; I've read some studies showing that the estimated particle sizes from the hydrometer portion of the test can be underestimated by up to two orders of magnitude due to the assumption of Stokes Law of falling spheres vs the disk or other shapes of real clay particles. This might be what we're running into but it seems unlikely because it's our first test and the distributions measured from the sieve analysis portion contradict results from the hydrometer portion. That is, the hydrometer portion is measuring all of the soil that passes the #10 sieve, which is estimated by percent suspended (calculated from specific gravity of the fluid+floating soils) and the estimated maximum particle size still in suspension (from Stokes Law). That same soil is later washed, dried, and measured again via a sieve analysis. The sieves are showing only 12% passing a #200, while the hydrometer analysis indicates 42% suspended after 2 minutes (so a particle size of about 0.037mm, about half of the .074mm of a #200 sieve).
Obviously these can't both be true, but we've triple checked the equations and they seem to be right. Is this a common problem with this test or is there something likely wrong with the calcs (spreadsheet attached)? I've double checked the measurements with this material and they are right. Also, is there a better place to ask questions about test-specific calculations than this forum? I've been looking around and can't find anything for that.
Thanks,
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RE: ASTM D422 Hydrometer Test vs Sieve Analysis