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Hydro lab manual 2013 - Copy

If the suspension is allowed to stand the particles

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Unformatted text preview: uivalent spherical particles. The density of a soil‐water suspension depends upon the concentration and specific gravity of the soil particles. If the suspension is allowed to stand, the particles will gradually settle out of the suspension, and the density will be decreased. The hydrometer is the instrument used to measure the density of the suspension at a known depth below the surface. The density measurement, together with knowledge of specific gravity of the soil particles, determines the percentage of dispersed soil particles in suspension which is determined using a calibrated hydrometer. Stokes’ law is used to calculate the maximum equivalent particle diameter for the material in suspension. A series of hydrometer measurements at known times Winter 2013 2 CIVE 153 – Earth Engineering Hydrometer Analysis Department of Civil and Environmental Engineering allows the determination of the percentages of particles finer than. Using a hydrometer and Stoke’s law the particle diameter (D) can be calculated using: L(cm) D(mm) K t (min) where D is the particle diameter in mm, K is the hydrometer constant based on the water temperature and viscosity (unit less), L is the hydrometer length in the fluid (cm) as shown in Figure 1 and t is the lapse time from the start of the test in minutes. Figure 1: Hydrometer grain size distribution test and length (L). Winter 2013 3 CIVE 153 – Earth Engineering Hydrometer Analysis Figure 2: Start of a soil hydrometer grain size distribution analysis. Department of Civil and Environmental Engineering APPARATUS AND MATERIALS 1. Sieves. 2. Brush for cleaning sieves 3. Balance ‐ sensitive to 0.01 g. 4. Oven. 5. Stirring apparatus ‐ mechanically operated, with an electrical motor able to turn a vertical shaft at a speed of not less than 10,000 r.p.m. without load. The shaft shall have a stirring paddle made of metal, plastic, or hard rubber. The paddle shall be not less than 19.0 mm or more than 38.1 mm above the bottom of the...
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