3_Soil-Classification (1).pdf

SOIL CLASSFICATION CLASSIFICATION OF SOIL Soil classification is a separation of soil into classes or groups each having similar characteristics and potentially similar behavior. A classification for engineering purposes should be based mainly on mechanical properties, e.g. permeability, stiffness...

SOIL CLASSFICATION CLASSIFICATION OF SOIL Soil classification is a separation of soil into classes or groups each having similar characteristics and potentially similar behavior. A classification for engineering purposes should be based mainly on mechanical properties, e.g. permeability, stiffness, and strength. The classification to which a soil belongs can be used in its description. Textural Classification (USDA & MIT Classification) Engineering Behavior (AASHTO & USCS) In a general sense, texture of soil refers to its surface appearance. The textural classification is based on the particle-size distribution of the percent of gravel, sand, silt, and clay size fractions present in a given soil. Soil texture is influenced by the size of the individual particles. TEXTURAL CLASSIFICATION Grain Size Classification Mechanical analysis is the determination of the size range of particles present in the soil, expressed as a percentage of the total dry weight. Two methods are used to find the particle- size distribution of soil: 1. Sieve Analysis — for particle sizes larger than 0.075 mm in diameter, and 2. Hydrometer Analysis — for particle sizes smaller than 0.075 mm in diameter. Sieve Analysis Gravelly Soil Sandy Soil Particle-Size Distribution (Sieve Analysis) A sieve analysis (or gradation test) is a practice or procedure to assess the particle-size distribution (also called gradation) of a granular material by allowing the material to pass through a series of sieves of progressively smaller mesh size and weighing the amount of material that is stopped by each sieve as a fraction of the whole mass. Particle-Size Distribution (Sieve Analysis) Soil Sample - Logarithmic Scale Example: Particle-Size Distribution Sieve No. Diameter Mass Retained Cumulative Mass Percent Passing 𝑴𝒂𝒔𝒔 𝑷𝒂𝒔𝒔𝒊𝒏𝒈 (mm) (grams) Retained (grams) (Percent Finer) % Passing = 𝑻𝒐𝒕𝒂𝒍 𝑴𝒂𝒔𝒔 4 4.76 7 7 99.12% 𝟕𝟗𝟕−𝟕 8 2.38 48 7+48 = 55 93.10% #4= x 100 = 99.12% 𝟕𝟗𝟕 10 2.00 60 115 85.57% 𝟕𝟗𝟕−𝟓𝟓 20 0.84 95 210 73.65% #8= x 100 = 93.10% 𝟕𝟗𝟕 40 0.42 149 359 54.96% 60 0.25 115 474 40.53% 80 0.18 210 684 14.18% 100 0.149 65 749 6.02% 200 0.074 36 785 1.51% PAN 12 797 0.00% TOTAL 797 Particle-Size Distribution (Sieve Analysis) This Soil - Logarithmic Scale Particle-Size Distribution (Sieve Analysis) Effective Size, 𝑫𝟏𝟎 = Diameter of 10% finer The effective size of a granular soil is a good measurement for the hydraulic conductivity and drainage of soil Uniformity Coefficient, 𝑪𝒖 𝐷60 𝐷60 = Diameter of 60% finer 𝐶𝑢 = 𝐷10 Coefficient of Gradation or Sorting Coefficient, 𝑺𝑶 Coefficient of Curvature, 𝑪𝑪 (𝐷30 )2 𝐷75 𝐶𝑐 = 𝑆𝑜 = 𝐷60 x 𝐷10 𝐷25 Suitability Number, SN 𝐷10 = Effective Size 𝐷25 = Diameter of 25% finer 3 1 1 𝐷30 = Diameter of 30% finer 𝑆𝑁 = + + (𝐷50 )2 (𝐷20 )2 (𝐷10 )2 𝐷50 = Average Grain Size 𝐷60 = Diameter of 60% finer 𝐷75 = Diameter of 75% finer Example: Particle-Size Distribution Sieve No. Diameter Mass Retained Cumulative Mass Percent Passing (mm) (grams) Retained (grams) (Percent Finer) 4 4.76 7 7 99.12% 8 2.38 48 7+48 = 55 93.10% Logarithmic Interpolation 10 2.00 60 115 85.57% 75% Finer 20 0.84 95 210 73.65% 60% Finer 40 0.42 149 359 54.96% 50% Finer 60 0.25 115 474 40.53% 20%, 25% & 30% Finer 80 0.18 210 684 14.18% 10% Finer 100 0.149 65 749 6.02% 200 0.074 36 785 1.51% PAN 12 797 0.00% TOTAL 797 Logarithmic Interpolation USE MODE > STAT > LOGARITHM INPUT (2 at a time ONLY) Logarithmic Normal X Y Diameter Percent Passing (Diameter) (Percent Finer) (mm) (Percent Finer) 2.00 85.57% 4.76 99.12% 0.84 73.65% 2.38 93.10% 0.42 54.96% 2.00 85.57% 75% Finer 0.25 40.53% 0.84 73.65% 60% Finer 0.18 14.18% 0.42 54.96% 50% Finer 0.149 6.02% 0.25 40.53% 20%, 25% & 30% Finer 0.18 14.18% Shift+Stat > Regression > “% finer” x̂ (i.e 10% x̂ ) 10% Finer 0.149 6.02% Summary: 0.074 1.51% 𝑫𝟏𝟎 = 0.163 mm 𝑫𝟓𝟎 = 0.351 mm 0.00% 𝑫𝟐𝟎 = 0.194 mm 𝑫𝟔𝟎 = 0.506 mm 𝑫𝟐𝟓 = 0.206 mm 𝑫𝟕𝟓 = 0.927 mm 𝑫𝟑𝟎 = 0.219 mm Particle-Size Distribution (Sieve Analysis) This Soil 𝑫𝟔𝟎 = 0.506 mm 𝑫𝟑𝟎 = 0.219 mm 𝑫𝟏𝟎 = 0.163 mm - Logarithmic Scale CALCULATION Sorting Coefficient, 𝑆𝑂 Effective Size, 𝐷10 = 0.163 mm 𝐷75 0.927 Uniformity Coefficient, 𝐶𝑢 𝑆𝑜 = = = 𝟐. 𝟏𝟐 𝐷25 0.206 𝐷60 0.506 𝐶𝑢 = = = 𝟑. 𝟏𝟎 𝐷10 0.163 Suitability Number, SN Coefficient of Gradation or 3 1 1 𝑆𝑁 = + + Coefficient of Curvature, 𝐶𝐶 (𝐷50 )2 (𝐷20 )2 (𝐷10 )2 (𝐷30 )2 (0.219)2 3 1 1 𝐶𝑐 = = = 𝟎. 𝟓𝟖𝟐 𝑆𝑁 = + + = 𝟗. 𝟒𝟏 𝐷60 x 𝐷10 0.506 x 0.163 (0.351)2 (0.194)2 (0.163)2 COMMENTS: For a soil to be well graded 𝐶𝑈 > 4 for gravel, 𝐶𝑈 > 6 for sands, 𝐶𝑈 ~1 for uniformly soils/ poorly graded soils. For soil to well graded 1< 𝐶𝐶