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Unformatted text preview: 36 CIVE 310 Soil Mechanics Hydrometer Analysis Section Assigned Due Before Lab: Read this Handout 37 HYDROMETER ANALYSIS Hydrometer analysis is the procedure generally adopted for determination of the particlesize distribution in a soil for the fraction that is finer than No. 200 sieve size (0.075 mm). The lower limit of the particlesize determined by this procedure is about 0.001 mm. In hydrometer analysis, a soil specimen is dispersed in water. In a dispersed state in the water, the soil particles will settle individually. It is assumed that the soil particles are spheres and Stoke&s law as can give the velocity of the particles 2 18 D w s = where : = velocity (cm/s) s = specific weight of soil solids (g/cm 3 ) w = unit weight of water (g/cm 3 ) = viscosity of water (g.s/cm 2 ) D = diameter of the soil particle If a hydrometer is suspended in water in which soil is dispersed (Figure 1), it will measure the specific gravity of the soilwater suspension at a depth L. The depth L is called the effective depth. So, at a time t minutes from the beginning of the test, the soil particles that settle beyond the zone of measurement (i.e., beyond the effective depth L) will have a diameter given by ( ) 2 2 3 10 ) ( ) . ( 18 / 60 (min) ) ( = mm D cm s g cm g t cm L w s Figure 1. Hydrometer suspended in the water in which the soil is dispersed 38 (min) ) ( ) ( 18 60 10 ) ( t cm L A t L mm D w s = = ) ( 30 ) ( 60 1800 w s w s A = = In the test procedure described here, the ASTM 152 H type of hydrometer will be used. From Figure 1 it can be seen that, based on the hydrometer reading (which increases from zero to 60 in the ASTM 152H type of hydrometer), the value of L will change. The magnitude of L can be given as L ) ( 2 1 2 1 C B A V L L L + = where; L 1 = distance between the top of hydrometer bulb to the mark for a hydrometer reading. For a hydrometer reading of zero, L 1 = 10.5 cm. For a hydrometer reading of 50 g/liter, L 1 = 2.3 cm. Thus, in general, for a given hydrometer reading = ) 50 3 . 2 5 . 10 ( 5 . 10 ) ( 1 cm L hydrometer reading L 2 = 14 cm V B = volume of the hydrometer bulb = 67.0 cm 3 A c = crosssectional area of the hydrometer cylinder = 27.8 cm 2 In addition to the above formula for calculation of L values, Table 1 can be used for calculation of L. That table shows the variation of L with hydrometer readings....
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 Spring '08
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