Soil Classification & Systems
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The document provides an overview of soil classification systems and their purposes, highlighting that soils exist as mixtures and possess varying engineering properties. It details methods for classifying soils based on particle size distribution, including mechanical and sedimentation analysis, as well as the Indian Standard Classification System (IS 1498-1970). Additionally, it explains the significance of particle size distribution in various engineering applications and outlines the common classifications for coarse and fine-grained soils.
Soil Classification & Systems
- 1. SOIL Classification & systems Arbaz Mubarak Kazi, B.E, M.E (Civil Engineering) Email: arbaazkazi91@gmail.com https://gtearchives.wordpress.com www.linkedin.com/in/arbaz-kazi-20747570 “Everyday is an Adventure When you are Civil Engineer”
- 2. CONTENTS ➢Purpose of soil Classification ➢Soil Classification systems ▪ Particle Size Classification ▪ Dry & Wet Sieve Analysis ▪ Sedimentation Analysis ▪ Stokes Law ➢ Indian Soil Classification System
- 3. Purpose of Soil Classification 1. Soils in nature rarely exist separately as gravel, sand, silt, clay or organic matter, but are usually found as mixtures with varying proportions of these components. 2. Classifying soils into groups with similar behavior, in terms of simple indices, can provide geotechnical engineers a general guidance about engineering properties of the soils through the accumulated experience. 3. Two commonly used approach for Classifying soils is based on particle distribution andAtterberg limits
- 4. Soil Classification Systems 1. Particle Size Classification 2. Textural Classification 3. Highway Research Board (HRB) Classification 4. Unified Soil Classification System (USCS) 5. Indian Standard Classification System (ISCS)
- 6. ▪ In this system soils arranged according to grain sizes. ▪ Terms such as gravel, sand, silt and clay are used to indicate grain sizes. ▪ These terms are used only as designation of particle sizes. ▪ They do not signify naturally occurring soil types, as naturally occurring soil are mixture of particles of different sizes. ▪ Plasticity characteristics of soil is not accounted for soil classification in this system. ▪ In India Particle size classification is done on the basis of IS 1498:1970 Introduction
- 8. US Bureau Soil Classification
- 9. IS Classification of Grain Size
- 10. ▪ The percentage of various sizes of soil particles in a given dry soil sample is found by mechanical analysis or particle size analysis. ▪ By mechanical sieve analysis is meant for separation of a soil into its different size fractions. ▪ The mechanical sieve analysis is performed in two stages as shown below: Particle Size Distribution Mechani cal Analysis Sieve Analysis Sedimentation or wet mechanical analysis
- 11. Sieve Analysis: • Sieve analysis consists of shaking the soil sample through a set of sieves that have progressively smaller openings. • In the Indian Standard (IS: 460- 1962), the sieves are designated by size of opening in (mm) as given. • The complete sieve analysis can be divided into two parts- the coarse analysis and fine analysis. Sieve Number Size of Opening (mm) 4 4.750 6 3.350 8 2.360 12 1.680 16 1.180 20 0.850 30 0.600 40 0.425 50 0.300 60 0.250 80 0.180 100 0.150 140 0.106 200 0.075
- 12. • An oven dried sample of soil is separated into two fractions by sieving it through a 4.75mm IS sieve. • The portion retained on it is termed as gravel fraction and is kept for coarse analysis, while portion passing through it is subjected to fine sieve analysis. • Soil passing 4.75mm I.S. Sieve and retained on 75micron I.S. Sieve contains no fines. Those soils can be directly dry sieved rather than wet sieving. SieveAnalysis
- 13. Mechanical Sieve Shaker Dry Sieving: • Take 500gm of the soil sample after taking representative sample by quartering. • Conduct sieve analysis using a set of standard sieves as given in the data sheet. • The sieving may be done either by hand or by mechanical sieve shaker for 10minutes.Weigh the material retained on each sieve. • The percentage retained on each sieve is calculated on the basis of the total weight of the soil sample taken. • From these results the percentage passing through each of the sieves is calculated. • Draw the grain size curve for the soil in the semi- logarithmic graph provided.
- 14. Wet Sieving: If the soil contains substantial quantity (say more than 5%) of fine particles, a wet a sieve analysis is required. All lumps are broken into individual particles. • Take 200gm of oven dried soil sample and soaked with water. • If deflocculation is required, 2% sodium hexametaphosphate solution is used instead of water. • The sample is stirred and left for soaking period of at least 1 hour. • The slurry is then sieved through 4.75 mm sieve and washed with a jet of water. • The material retained on the sieve is the gravel fraction, which should be dried in oven and weighed.
- 15. • The material passing through 4.75mm sieve is sieved through 75μ sieve. • The material is washed until the water filtered becomes clear. • The soil retained on 75-micron sieve is collected and dried in oven. • It is then sieved through the sieve shaker for ten minutes and retained material on each sieve is collected and weighed. • The material that would have been retained on pan is equal to the total mass of soil minus the sum of the masses of material retained on all sieves. • Draw the curve for the soil in the semi-logarithmic graph to obtain grain size distribution curve. Wet Sieving:
- 18. • Well graded Soil will have particles from almost all the size ranges and will give a stable mix. • Gap graded Soil will have deficiency of certain particles of a particular size range. • Uniformly or poorly graded Soil will have almost same size or from narrow range of particle sizes of soil in the sample. This sample will contain single size soil.
- 19. Coefficient of curvature (Cc) should lie between 1 and 3 for well grade gravel and sand. Cu should be more than 4 for gravel and more than 6 for sand.
- 20. ❑ Sieve analysis was performed on 1000 gm of dry soil sample and the following observations were made as given: Use particle size classification system and classify the soil, also find Cu and Cc Sieve Size (mm) Mass Retained (gm) 20 33 10 49 4.75 85 2 140 1 160 0.6 142 0.425 118 0.3 82 0.212 56 0.15 35 0.075 23
- 21. Sieve Size (mm) Mass Retained (gm) % Mass Retained % Cumulative Retained % Finer 20 33 3.3 3.3 96.7 10 49 4.9 8.2 91.8 4.75 85 8.5 16.7 83.3 2 140 14 30.7 69.3 1 160 16 46.7 53.3 0.6 142 14.2 60.9 39.1 0.425 118 11.8 72.7 27.3 0.3 82 8.2 80.9 19.1 0.212 56 5.6 86.5 13.5 0.15 35 3.5 90 10 0.075 23 2.3 92.3 7.7
- 23. D60 1.419 D30 0.465 D10 0.150 Cu = D60/D10 = 1.419/0.150 = 9.46 > 6, Hence it is Sand Cc = D302/(D60*D10) = 0.4652/(1.419*0.150) = 1.01 > 1, Hence it is well graded The soil may be classified as Well Graded Sand (SW)
- 24. Importance of Particle Size Distribution 1. Used for the soil classification. 2. Used to design drainage filter. 3. Used to select fill materials of embankments, earth dams, road sub-base materials. 4. Used to estimate performance of grouting, chemical injection and dynamic compaction. 5. Effective Size, D10, can be correlated with the hydraulic conductivity. 6. Estimate approximate value of co-efficient of permeability. 7. Used to determine susceptibility of soil to frost action. 8. Used of Soil stabilization and pavement design.
- 25. ▪ For particles ≤ 0.075 mm (silt and clay fractions) sedimentation methods based on Stokes law are used to deduce particle size distribution. ▪ Soil particles settle in aqueous solution attaining terminal velocities proportional to their mass and size. ▪ The amount of suspended soil after a given settling time is used to determine particle size fractions. ▪ The amount of soil in suspension is determined by either extracting a sample by the pipette method or from a direct hydrometer reading. Particle Size Distribution - Sedimentation
- 26. • Buoyancy and drag forces act against the gravitational force. • A spherical soil particle D=5 um reaches 99% of its terminal velocity in aqueous solution within 0.017ms, and for D=1 mm the time is 0.68s. • Buoyancy Force (weight of displaced liquid)Drag Force (exerted by the surrounding liquid) Gravitational Force Stokes Law Three forces acting on a spherical particle.
- 27. The three forces acting upon the settling particle quickly equilibrate and the particle reaches a constant settling velocity. We can solve the force balance equation to obtain the settling velocity Since we know that velocity equals length per time we can calculate the time particles of a certain size need to settle through a distance h: t is the time required for particles of a certain size to settle below a certain depth h. Stokes Law
- 28. • Particles are large enough to be unaffected by the thermal (Brownian) motion of the fluid molecules. • All particles are rigid, spherical, and smooth. • All particles have the same density. • The suspension is dilute enough that particles do not interfere with each other • Fluid flow around the particles is laminar. That means no particle exceeds the critical velocity for the onset of turbulence. • In practice we know that soil particles are neither spherical nor smooth. Hence the diameter calculated from Stokes law does not necessarily correspond to the actual dimensions of the particles. We rather receive an effective or equivalent settling diameter. Stokes Law - Limitations
- 29. Methods of Sedimentation Analysis Pipette Method Hydrometer Method
- 30. IS SOIL CLASSIFICATION SYSTEM IS: 1498-1970 describes the Indian Standard on Classification and Identification of Soils for general engineering purposes. It is similar to U.S. Soil classification system except that the U.S. Soil classification system has 15 groups while this system has 18 groups Significant provisions of this system are given below: Soils shall be broadly divided into three divisions: 1. Coarse-grained Soils: More than 50% of the total material by weight is larger than 75μ IS Sieve size. 2. Fine-grained Soils: More than 50% of the total material by weight is smaller than 75μ IS Sieve size. 3. Highly Organic Soils and Other Miscellaneous Soil Materials: These soils contain large percentages of fibrous organic matter, such as peat, and particles of decomposed vegetation. In addition, certain soils containing shells, concretions, cinders and other non-soil materials in sufficient quantities are also grouped in this division.
- 31. Coarse-grained soils shall be divided into two sub-divisions: • Gravels: More than 50% of coarse fraction (+ 75 μ) is larger than 4.75 mm IS Sieve size. • Sands: More than 50% of Coarse fraction (+ 75 μ) is smaller than 4.75 mm IS Sieve size. Fine-grained soils shall be divided into three sub-divisions: ❖ Silts and clays of low compressibility: Liquid limit less than 35% (L). ❖ Silts and clays of medium compressibility: Liquid limit greater than 35% and less than 50% (I). ❖ Silts and clays of high compressibility: Liquid limit greater than 50 (H). The coarse-grained soils shall be further sub-divided into eight basic soil groups, and the fine- grained soils into nine basic soil groups; highly organic soils and other miscellaneous soil materials shall be placed in one group
- 32. The symbols used to designate soil in this system are GW – well graded gravel GP – poorly graded gravel GM – silty gravel GC – clayey gravel SW – well graded sand SP – poorly graded sand SM – silty sand SC – clayey sand CL – clay of low plasticity CI – clay of medium plasticity CH – clay of high plasticity ML – silt of medium plasticity MI – silt of medium plasticity MH – silt of high plasticity OL – organic silt and clays of low plasticity OI – organic silt and clays of medium plasticity OH – organic silt and clays of high plasticity Pt – peat
- 33. IS SOIL CLASSIFICATION SYSTEM For Video, Click the link: https://youtu.be/0DyP-LdKByU