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Unformatted text preview: The University of Iowa Dept. of Civil & Env. Engg. 53:030 Soil Mechanics Fall Semester Lab. No. 2: Measuring Grain Size Distributions of Soils Equipment: Sieving: mass balance, nest of sieves, sieve shaker. Hydrometer: stirring apparatus, 1000 ml cylinder, beaker, thermometer, evaporating dish. In this lab session, you will be given two soil samples: a sample of coarse-grained soil named FI-6, and a sample of fine-grained soil named FI-10. You will use sieving to measure the GSD (grain size distribution) of the coarse soil, and hydrometer testing to measure the GSD of the fine-grained soil. I. Coarse-grained Soils A. Procedure for sieving coarse-grained soil . 1. Obtain and weigh approximately 500 grams of oven-dried soil. 2. If necessary, break the soil sample into individual grains using the soil grinder, and/or the mortar and pestle. ( The idea is to break up the soil into individual grains rather than to break the grains themselves. ) 3. Collect the following sieves: #s 20,40,60,100,140,200 and pan. After making sure that each sieve is clean (free of loose soil grains), obtain the mass of each sieve to within 0.1g. 4. Assemble a nest of sieves with the largest sized openings at the top, and with the smallest at the bottom. Make sure that the pan is in place at the base of the stack. 5. Pour the soil sample into the top of the nest. After placing a cap on the stack, place the stack of sieves into the shaking apparatus. Using the apparatus, shake the stack of sieves for 1015 minutes. 6. After shaking, remove the stack from the apparatus, and carefully separate the sieves, making sure not to spill the soil. Obtain the combined mass of each sieve and the soil it retains. 7. If a significant fraction of the total specimen ( say 10% by mass ) is retained on the #200 sieve, then the retained soil must be washed through the sieve. (Ask the lab instructor for assistance in this case.) 8. Compute the mass of dry soil retained on each sieve, and plot the grain size distribution for the soil. The sum of soil masses retained on all the sieves should be almost equal to that of the original soil mass. II. Hydrometer Testing of Fine-grained Soils A. Background: Hydrometer testing is the procedure commonly adopted for determination of the grain size distribution in soils with 0.075mm. In this test, a soil specimen is dispersed in a calgon-water solution so that the particles will settle individually. For simplicity, it is assumed that the individual soil particles are spheres, and that the average settling velocity for each particle is given by Stokes law: = s f 18...
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- Fall '09