LAB MANUAL 4HydrometerAnalysis

LAB MANUAL 4HydrometerAnalysis - 36 CIVE 310 Soil Mechanics...

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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 particle-size distribution in a soil for the fraction that is finer than No. 200 sieve size (0.075 mm). The lower limit of the particle-size 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 soil-water 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 152-H 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 = cross-sectional 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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LAB MANUAL 4HydrometerAnalysis - 36 CIVE 310 Soil Mechanics...

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