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Hydrometer Problem combining ASTM D6913 and D7928

Pu73

Civil/Environmental
Mar 21, 2025
1
Im facing the issue of having a jump in the gradation curve when combining data from sieve analysis D6913 and hydrometer D7928
Basically the jump is up not down, which means if my passing #200 is 25%, the passing particle size 0.05mm is 30%. Which does not make sense.
Its organic soil and has a lot of small wood particles that can not be easily removed from the sample. I know this interfere with the accuracy of hydrometer results, but D7928 did not address this issue specifically.
The curve does not smoothen unless I went with SG=3 for example. Which does not make sense.
Any tips please?
 
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Did you wash and shake the hydrometer specimen for the sieve test? If not, and you used two separate specimens as per the ASTM STPs, then it's possible that the hydrom specimen may have had a greater percentage of P200 than the shook gradation sample and this will cause an issue.
 

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