Analysis Of Sieve Analysis

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Figure 4.1: Sieve Analysis • Fine To determine the grain size distribution of material passing the 75m sieve the hydrometer method is commonly used. The soil is mixed with water and a dispersing agent, stirred vigorously, and then allowed to settle to the bottom of a measuring cylinder. As the soil particles settle out of suspension, the specific gravity of the mixture reduces. One hydrometer is used to record the variation of specific gravity with time, Figure 4.2. By making use of Stoke’s Law, which relates the terminal velocity of a free falling sphere to its diameter, the test data is reduced to provide particle diameters and the % by weight of the sample finer than a particular particle size. Figure 4.2: Sedimentation Analysis Retained in each sieve (gm) 2 Percentage on each sieve Rn 3 Cumulative %tage retained on each sieve Rn 4 % finer 100 - Rn 5 Remarks Draw graph of log sieve size vs % finer. The graph is known as grading curve (see Figure 4.3). 2. Obtain diameters designated as D10, D30, D60 corresponding to 10%, 30% and 60% finer from the graph. 3. Determine the percentages of Clay, silt, fine sand, coarse sand and gravel : Clay = ˂ 0.002 mm; Silt = 0.002 - 0.02 mm; Fine sand = 0.02 - 0.2 mm; Coarse sand = 0.2 - 2.0 mm Gravel = ˃ 2.0 mm 4. Calculate Cu and Cg Uniformity Coefficient Cu = D60/D10 4.4 Coefficient of Gradation or Coefficient of Curvature Cg Cg = (D30)2/ D60 x D10 4.6 5. Comment on the results and soil Besides determining the particle sizes and frequency of their occurrence, some conclusions can be drawn on their grading. A soil can be said to be well graded or poorly graded or gap-graded depending on the particle size distribution curve. 6. The number or sizes of sieves in the nest depends on the type of soil and the distribution of the particle sizes. Sieve numbers 4, 10, 40, and 200 are typically used in classifying

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