Figure 13-13.—Apparatus for grain size distribution by hydrometer analysis.HYDROMETER ANALYSISYou learned in the EA3 TRAMAN that a soil isconsidered susceptible to frost when it contains 3percent or more by weight of particles smaller than0.020 mm in diameter. To determine whether or not asoil contains an excessive amount of that size particle,you must perform a particle-size analysis of thematerials passing the No. 200 (0.074-mm) sieve. You dothis by hydrometer analysis. This TRAMAN discussionidentifies the items used for a hydrometer analysis andwill briefly summarize the procedures used. For a fulldiscussion of the procedures, you should refer toNAVFAC MO-330 or to ASTM D 422. You also shouldreview the topic of hydrometer analysis on page 15-24of the EA3 TRAMAN before continuing with thefollowing discussion.ApparatusFigure 13-13 shows some of the items that you willneed to perform a hydrometer analysis. Another itemyou will need is an ASTM hydrometer (fig. 13-14).ASTM hydrometers are graduated by the manufacturerto read in either specific gravity or in grams per liter andare calibrated at a standard temperature of 68°F (20°C).Other needed items are a dispersion cup and stirrer (fig.13-15), a thermometer accurate to 1°F (0.5°C), and aclock, or watch, with a second hand.Sample Preparation and Test ProcedureSamples for hydrometer analysis are taken fromrepresentative material finer than the No. 10 sieve. Theapproximate size of the sample varies according to thetype of soil being tested. For clays and silty soils, you13-16
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