Ex 4 sieve analysis and soil classification
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1) The document describes a laboratory experiment to determine the particle size distribution of a soil sample through sieve analysis according to IS: 2720 (Part IV) - 1985. Sieves ranging from 75mm to 75 micron are used to separate the soil particles by size. 2) The percentage of soil retained on each sieve is recorded and a particle size distribution curve is plotted to classify the soil. Parameters like D10, D30, D60 and coefficients of curvature (Cc) and uniformity (Cu) are calculated. 3) Based on the particle size distribution curve characteristics like grading, permeability and shear strength can be estimated to classify the soil and determine its engineering suitability.
Ex 4 sieve analysis and soil classification
- 1. Experiment No: 04 Date: SIEVE ANALYSIS, PARTICLE SIZE DETERMINATION AND IS CLASSIFICATION Object and scope: Quantitative determination of grain size distribution of given soil sample by Dry Sieve method, plot distribution curve and classify given soil sample as per the criteria given in IS: 2720 (Part IV) - 1985. Reference: IS: 2720 (Part IV) – 1985 Theory: Grain size analysis means determination of percentage by means of fraction of different sizes of particles in the soil sample. It is also known as mechanical analysis. Soil classification is required to identify wither the given soil is suitable for different engineering purpose. Sieve analysis is adapted to find the distribution of grain sizes larger than 75 micron IS Sieve. The dry sieve method is suitable for non-cohesive soils. Particle size distribution curve is obtained after plotting all the results of mechanical analysis on semi- logarithmic graph. The curve gives an idea about the type and gradation of soil. Particle size distribution curves of different soils are shown in figure. Curve with a hump, such as curve- A, represents the soil in which some of the intermediate size particles are missing. Such a soil is called Gap-graded or skip graded soil. Flat S-Curve such as curve-B, represents a soils which contains the particles of different sizes in good preparation. Such a soil is called a well-graded or uniformly graded soil. Steep curve such as curve-C, indicates a soil containing the particles of almost the same size. Such soils are known as Uniform soils. The particles size distribution curve also reveals whether a soil is coarse – graded or fine-graded. A curve situated higher up and to the left (Curve-D) indicates a relatively fine grained soil, where as a curve situated to the right (Curve E) indicates a coarse grained soil. Fig.1. Grading of Soil
- 2. Equipments: 1) Balance- sensitive to 0.1% of the weight of sample to be weighed 2) Sieves- 100mm, 75mm, 19mm,10 mm,6.3mm, 4.75mm, 2.36mm, 1.18mm, 600 micron, 300 micron, 150 micron and 75 micron IS sieve conforming to the requirement of IS: 460 3) Rubber Pestle and Mortar Preparation of sample: The soil sample received from the field shall be prepared as specified in IS: 2720. The soil fractions retained on and passing 4.75mm IS sieve shall be taken separately for the analysis. Depending on the maximum size of material present in substantial quantities in the soil, the mass of soil sample taken for analysis may be as follows: maximum size of material present in substantial quantities (mm) Mass of soil taken for test (kg) 75 60 40 25 25 13 19 6.5 12.5 3.5 10 1.5 6.5 0.75 4.75 0.4 Procedure: 1) The sieves are arranged in the descending order of their size from top. 2) Soil sample of known weight is put into the topmost sieve, the sieve set is fixed on a sieve shaker and shall be agitated so that the sample rolls in irregular motion over the sieve. No particle shall be pushed through the sieve. The material retained on the sieve shall be rubbed with the rubber pestle to make sure that only individual particles are retained on the sieve. Care shall be taken to ensure that sieving is complete. A minimum of 10 minutes shaking shall be used. 3) The soil fraction retained in each sieve shall be carefully collected in containers and the mass of each fraction is determined and recorded. 4) The cumulative mass of fraction retained on each sieve shall be calculated. The percentage of soil fraction retained on each sieve shall be calculated on the basis of the mass of the sample passing 4.75mm IS Sieve taken for analysis. 5) Plot particle size distribution curve, percentage finer (N) is taken as ordinate on a natural scale and particle diameter (D) on logarithmic scales as the abscissa. 6) Find D10, D 30 and D60. D10 represents a particle size in mm such that 10% of the particles are finer than this size. D30 means 30% of particles are finer that this size and D60 means 60% of the particles are finer than the size of the particle at 60% point on the curve. 7) Calculate coefficient of curvature and uniformity (i.e. Cc and Cu). 8) Depending upon values of Cc, Cu and shape of particle size distribution curve, determine the grading of soil as per IS classification.
- 3. Observation Table: Sr. No. IS sieve size Mass of soil retained (gm) % mass retained Cumulative % % finer Calculations: Coefficient of Uniformity Cu = D10 D60 Coefficient of curvature Cc = (D30 )2 (D10 × D60 ) Result: Soil can be classified as: Uses of particle size distribution curve: 1) For classification of coarse grained soils. 2) For the design of drainage filters. 3) It gives idea about shear strength of soil. Generally a well-graded compacted soil has higher shear strength. 4) It gives information about Compressibility of soil. A uniform soil is more compressible than a well graded soil 5) Useful in soil stabilization and design of pavements 6) The coefficient of permeability of a coarse grained soil can be determined from the particle size. 7) The particle size distribution curve of a residual soil may indicate the age of the soil. 8) It may indicate the mode of deposition of a soil, for example a gap graded soil indicated deposition by two different agencies.
- 4. Fig.2. Set of Sieves arranged in descending order of sizes.