Soil Mechanics-I(CENG-2202) Chapter 2 : Simple Soil Properties - 16 - Department of Civil Engineering, Faculty of Technology Addis Ababa University2.2 GRAIN SIZE DISTRIBUTION Determination of the size range of particles present in a soil is useful in a wide range of areas such as soil classification, estimation of hydraulic conductivity, selection of aggregates for concrete and selection of material for grouting and chemical stabilization. The main engineering properties of soils are permeability, compressibility, and shearstrength. The tests required for determination of engineering properties are generally elaborate and time-consuming. It may often be necessary to have rough assessment of the engineering properties without conducting elaborate tests. This is possible if grain size distribution and consistency limits (to be discussed in the next section) are determined. Various correlations between these physical properties and other soil properties are then employed. The method of determination of the size range of particles present in a soil known usually as mechanical analysis or particle size analysis is achieved by one or a combination of the following two techniques: a.Sieve analysis – used to determine the average grain diameter of coarse-grained soils having particles larger than 0.075mm, and b.Hydrometer analysis – used to determine the size distribution of fine-grained soils having particles less than 0.075mm. SIEVE ANALYSIS This method involves shaking of a known weight of soil sample through a stack of sieves that have progressively finer mesh from top to bottom. The particle diameter in this screening process is the maximum particle dimension to pass through the square hole of a particular mesh size. Prior to conduction sieve analysis the soil must first be oven-dried. All lumps are then broken into smaller particles. In the case of cohesive soils, breaking the lumps into individual particles may not be easy. In this case, the soil may be mixed with water to make slurry and then washed through the sieve, the process is thus known as wet sieving. Some common standard sieves with their standard numbers (US standard) and opening sizes are listed below. Sieve no. Opening (mm) 4 4.75 10 2.00 20 0.85 40 0.425 100 0.15 200 0.075
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