Soil Classification Lecture Notes PDF

CLASSIFICATION OF SOIL OBJECTIVES: ✓ Recognize the different methods used in the classification of soil. ✓ Identify the type of soil using the different classification system. ✓ Know how to classify soil ✓ Solved problems involving the Classification of soil....

CLASSIFICATION OF SOIL OBJECTIVES: ✓ Recognize the different methods used in the classification of soil. ✓ Identify the type of soil using the different classification system. ✓ Know how to classify soil ✓ Solved problems involving the Classification of soil. Prepared by: Gine O. G. (KSU-CEIT) CLASSIFICATION OF SOIL: INTRODUCTION Classification systems provide a common language SOIL to concisely express the general characteristics of CLASSIFICATION soils, which are infinitely varied, without detailed descriptions. Classification Textural by Engineering Classification behavior U.S Department of AASHTO Unified Soil agriculture (USDA) Classification Classification Classification System System (USCS) System Prepared by: Gine O. G. (KSU-CEIT)  In a general sense, texture of soil refers to its surface appearance. Soil texture is influenced by the size of the individual particles present in it CLASSIFICATION Sand size: USDA 2.0 to 0.05 mm in diameter METHOD Silt size: TEXTURAL 0.05 to 0.002 mm in diameter Clay size: smaller than 0.002 mm in diameter In the textural classification system, the soils are named after their principal components, such as sandy clay, silty clay, and so forth. Textural classification systems developed by the U.S. Department of Agriculture (USDA). This classification method is based on the particle-size limits as 𝑆𝑜𝑢𝑟𝑐𝑒: 𝐹𝑢𝑛𝑑𝑎𝑚𝑒𝑛𝑡𝑎𝑙𝑠 𝑜𝑓 𝐺𝑒𝑜𝑡𝑒𝑐ℎ𝑛𝑖𝑐𝑎𝑙 𝐸𝑛𝑔𝑖𝑛𝑒𝑒𝑟𝑖𝑛𝑔, 4𝑡ℎ 𝐸𝑑𝑖𝑡𝑖𝑜𝑛 𝑏𝑦 𝐵𝑟𝑎𝑗𝑎 𝑀. 𝐷𝑎𝑠 described under the USDA system Prepared by: Gine O. G. (KSU-CEIT) Classify the following soils according SOIL A: to USDA textural classification system. Particle-size SOIL Gravelly clay loam distribution A B C D (%) Gravel 10 21 0 12 Sand 20 12 18 22 Silt 41 35 24 26 Clay 29 32 58 40 Modified % of sand, silt and clay Particle-size SOIL distribution A B C D (%) Sand 22.2 15.2 18 25 Silt 45.6 44.3 24 29.5 Clay 32.2 40.5 58 45.5 %sand Modified % sand = x 100 100 − %gravel %silt Modified % silt = x 100 100 − %gravel %clay Modified % clay = x 100 100 − %gravel USDA SAMPLE PROBLEM SOLVING: Prepared by: Gine O. G. (KSU-CEIT) method Classify the following soils according SOIL B: to USDA textural classification system. Particle-size SOIL Gravelly Silty Clay distribution A B C D (%) Gravel 10 21 0 12 Sand 20 12 18 22 Silt 41 35 24 26 Clay 29 32 58 40 Modified % of sand, silt and clay Particle-size SOIL distribution A B C D (%) Sand 22.2 15.2 18 25 Silt 45.6 44.3 24 29.5 Clay 32.2 40.5 58 45.5 %sand Modified % sand = x 100 100 − %gravel %silt Modified % silt = x 100 100 − %gravel %clay Modified % clay = x 100 100 − %gravel USDA SAMPLE PROBLEM SOLVING: Prepared by: Gine O. G. (KSU-CEIT) method Classify the following soils according SOIL C: to USDA textural classification system. Particle-size SOIL Clay distribution A B C D (%) Gravel 10 21 0 12 Sand 20 12 18 22 Silt 41 35 24 26 Clay 29 32 58 40 Modified % of sand, silt and clay Particle-size SOIL distribution A B C D (%) Sand 22.2 15.2 18 25 Silt 45.6 44.3 24 29.5 Clay 32.2 40.5 58 45.5 %sand Modified % sand = x 100 100 − %gravel %silt Modified % silt = x 100 100 − %gravel %clay Modified % clay = x 100 100 − %gravel USDA SAMPLE PROBLEM SOLVING: Prepared by: Gine O. G. (KSU-CEIT) method Classify the following soils according SOIL D: to USDA textural classification system. Particle-size SOIL Gravelly Clay distribution A B C D (%) Gravel 10 21 0 12 Sand 20 12 18 22 Silt 41 35 24 26 Clay 29 32 58 40 Modified % of sand, silt and clay Particle-size SOIL distribution A B C D (%) Sand 22.2 15.2 18 25 Silt 45.6 44.3 24 29.5 Clay 32.2 40.5 58 45.5 %sand Modified % sand = x 100 100 − %gravel %silt Modified % silt = x 100 100 − %gravel %clay Modified % clay = x 100 100 − %gravel USDA SAMPLE PROBLEM SOLVING: Prepared by: Gine O. G. (KSU-CEIT) method Classify the soil according to USDA textural classification system. PROBLEM 1 Opening (mm) % Finer 4.75 100 2 94.51 0.850 86.28 0.150 9.33 0.050 1.00 0.002 0.65 USDA STUDENT ACTIVITY method Classify the soil according to USDA textural classification system. PROBLEM 2 Opening (mm) % Finer 2.00 100 0.075 70 0.050 65 0.005 32 0.002 15 USDA STUDENT ACTIVITY method Classify the soil according to USDA textural classification system. PROBLEM 3 Particle-size distribution SOIL (% Finer) A B Gravel 20 0 Sand 8 17 Silt 48 57 Clay 24 26 USDA STUDENT ACTIVITY method  AASHTO CLASSIFICATION SYSTEM AASHTO CLASSIFICATION SYSTEM The AASHTO system of soil classification was developed in 1929. According to this system, soil is classified into seven major groups: A-1 through A-7. Soils classified under groups A-1, A-2, and A-3 are granular materials of which 35% or less of the particles pass through the No. 200 sieve. Soils of which more than 35% pass through the No. 200 sieve are classified under groups A-4, A-5, A-6, and A-7. These soils are mostly silt and clay-type materials. Prepared by: Gine O. G. (KSU-CEIT) AASHTO CLASSIFICATION SYSTEM This classification system is based on the ff. criteria: Gravel: fraction passing the 75-mm (3-in.) sieve and retained on the No. 10 (2-mm) U.S. sieve GRAIN SIZE Sand: fraction passing the No. 10 (2-mm) U.S. sieve and retained on the No. 200 (0.075-mm) U.S. sieve Silt and clay: fraction passing the No. 200 U.S. sieve The term silty is applied when the fine fractions of the soil PLASTICITY have a plasticity index of 10 or less. The term clayey is applied when the fine fractions have a plasticity index of 11 or more (size larger than 75 mm) are encountered, they are excluded BOULDERS & from the portion of the soil sample from which classification COBBLES is made. However, the percentage of such material is recorded. Prepared by: Gine O. G. (KSU-CEIT) AASHTO CLASSIFICATION SYSTEM 𝑆𝑜𝑢𝑟𝑐𝑒: 𝐹𝑢𝑛𝑑𝑎𝑚𝑒𝑛𝑡𝑎𝑙𝑠 𝑜𝑓 𝐺𝑒𝑜𝑡𝑒𝑐ℎ𝑛𝑖𝑐𝑎𝑙 𝐸𝑛𝑔𝑖𝑛𝑒𝑒𝑟𝑖𝑛𝑔, 4𝑡ℎ 𝐸𝑑𝑖𝑡𝑖𝑜𝑛 𝑏𝑦 𝐵𝑟𝑎𝑗𝑎 𝑀. 𝐷𝑎𝑠 AASHTO CLASSIFICATION SYSTEM Plot of the range of the liquid limit and the plasticity index or soil that fall into group A-2, A-4, A-5, A-6, and A-7 Prepared by: Gine O. G. (KSU- 𝑆𝑜𝑢𝑟𝑐𝑒: 𝐹𝑢𝑛𝑑𝑎𝑚𝑒𝑛𝑡𝑎𝑙𝑠 𝑜𝑓 𝐺𝑒𝑜𝑡𝑒𝑐ℎ𝑛𝑖𝑐𝑎𝑙 𝐸𝑛𝑔𝑖𝑛𝑒𝑒𝑟𝑖𝑛𝑔, 4𝑡ℎ 𝐸𝑑𝑖𝑡𝑖𝑜𝑛 𝑏𝑦 𝐵𝑟𝑎𝑗𝑎 𝑀. 𝐷𝑎𝑠 CEIT) AASHTO CLASSIFICATION SYSTEM To evaluate the quality of a soil as a highway subgrade material, one must also incorporate a number called the group index (GI) 𝐆𝐈 = (𝐅₂₀₀ − 𝟑𝟓)[𝟎. 𝟐 + 𝟎. 𝟎𝟎𝟓(𝐋𝐋 − 𝟒𝟎)] + 𝟎. 𝟎𝟏(𝐅₂₀₀ − 𝟏𝟓)(𝐏𝐈 − 𝟏𝟎) ✓A negative value for GI is taken as 0. ✓The group index calculated is rounded off to the nearest whole number Ex: GI =3.4 then GI=3; GI =3.5 then GI=4 ✓The group index of soil/s belonging to group/s A-1-a, A-1-b, A-2-4, A-2-5, and A-3 is always 0. ✓When calculating the group index for soils that belong to groups A-2-6 and A-2-7, use the partial group index for PI, or use equation: 𝐆𝐈 = 𝟎. 𝟎𝟏(𝐅₂₀₀ − 𝟏𝟓)(𝐏𝐈 − 𝟏𝟎) Prepared by: Gine O. G. (KSU- CEIT)  Sample Problem: Classify the following soils according to AASHTO SOIL % passing Sieve No. Dia. (mm) A B 10 2 100 40 0.425 80 200 0.075 58 95 Liquid Limit 0.250 30 60 Plasticity index 0.150 10 40 Prepared by: Gine O. G. (KSU-CEIT)  Sample Problem Solution: SOIL A: Since 58% passed No. 200, it falls under Silt-Clay materials 𝐆𝐈 = (𝐅^𝟐𝟎𝟎 − 𝟑𝟓)[𝟎. 𝟐 + 𝟎. 𝟎𝟎𝟓(𝐋𝐋 − 𝟒𝟎)] + 𝟎. 𝟎𝟏(𝐅^𝟐𝟎𝟎 − 𝟏𝟓)(𝐏𝐈 − 𝟏𝟎) 𝐆𝐈 = (𝟓𝟖 − 𝟑𝟓)[𝟎. 𝟐 + 𝟎. 𝟎𝟎𝟓(𝟑𝟎 − 𝟒𝟎)] + 𝟎. 𝟎𝟏(𝟓𝟖 − 𝟏𝟓)(𝟏𝟎 − 𝟏𝟎) 𝐀 − 𝟒 (𝟑) 𝐆𝐈 = 𝟑. 𝟒𝟓 ≃ 𝟑 Prepared by:  Sample Problem Solution: SOIL B: Since 95% passed No. 200, it falls under Silt-Clay materials PI = 40 > LL - 30 𝐆𝐈 = (𝐅^𝟐𝟎𝟎 − 𝟑𝟓)[𝟎. 𝟐 + 𝟎. 𝟎𝟎𝟓(𝐋𝐋 − 𝟒𝟎)] + 𝟎. 𝟎𝟏(𝐅^𝟐𝟎𝟎 − 𝟏𝟓)(𝐏𝐈 − 𝟏𝟎) 𝐆𝐈 = (𝟗𝟓 − 𝟑𝟓)[𝟎. 𝟐 + 𝟎. 𝟎𝟎𝟓(𝟔𝟎 − 𝟒𝟎)] + 𝟎. 𝟎𝟏(𝟗𝟓 − 𝟏𝟓)(𝟒𝟎 − 𝟏𝟎) 𝐆𝐈 = 𝟒𝟐 Prepared by: 𝐀 − 𝟕 − 𝟔 (𝟒𝟐) Gine O. G. (KSU-CEIT) EXERCISE: Classify the following soils according to AASHTO SOIL % passing Sieve No. Dia. (mm) A B 4 4.75 100 100 10 2 92 98 20 0.850 87 92 40 0.425 53 84 60 0.250 42 79 100 0.150 26 70 200 0.075 17 63 LL 35 47 PL 20 24 Prepared by: Gine O. G. (KSU-CEIT)  ASSESSMENT: Classify the following soils according to AASHTO ATTERBERG LIMITS SIEVE NUMBER ( % passing) SOIL CLASSIFICATION SOIL W (%) LL PL #4 #10 #20 #40 #60 #200 PI GROUP Classification GI A 22.95 51 22 94 62 35 25 7 4 B 25.15 55 31 100 99 99 97 C 35.85 62 37 99 53 38 29 16 2 D 47.61 70 39 90 50 31 26 15 5 E 21.38 72 24 92 63 41 27 18 1 F 49.87 47 35 100 99 98 97 95 G 33.51 68 30 96 57 45 21 15 3 H 39.09 55 28 90 53 39 21 18 0 I 43.91 44 29 100 99 99 98 97 J 46.24 47 28 98 52 30 23 18 2  UNIFIED SOIL CLASSIFICATION SYSTEM  COARSE-GRAINED SOIL FINE-GRAINED SOIL UNIFIED SOIL CLASSIFICATION SYSTEM ✓Gravelly and sandy in nature ✓Silty and Clayey in nature ✓Less than 50% passing through ✓50% or more passing through No. 200 sieve. No. 200 sieve. ✓Group symbol : ✓Group symbol : Starts with M, Start with G or S C, O Pt G – gravel or gravelly soil M – Inorganic silt S – Sand or sandy soil C – Inorganic clay O – Organic silts and clays Pt – peat and muck and other highly organic soils Other symbol for classification W – Well graded P – Poorly graded L – Low plasticity (LL50) Prepared by: Gine O. G. (KSU-CEIT) UNIFIED SOIL CLASSIFICATION SYSTEM For proper classification according to this system, some or all of the following information must be known: ✓Percent of gravel—that is, the fraction passing the 76.2-mm sieve and retained on the No. 4 sieve (4.75-mm opening) ✓Percent of sand—that is, the fraction passing the No. 4 sieve (4.75-mm opening) and retained on the No. 200 sieve (0.075-mm opening) ✓Percent of silt and clay—that is, the fraction finer than the No. 200 sieve (0.075-mm opening) ✓Uniformity coefficient (Cu) and the coefficient of gradation (Cc) ✓Liquid limit and plasticity index of soil passing the No. 40 sieve  The group symbols for coarse-grained gravelly soils: UNIFIED SOIL CLASSIFICATION SYSTEM GW, GP, GM, GC, GC-GM, GW-GM, GW-GC, GP-GM, and GP-GC. The group symbols for fine-grained soils: CL, ML, OL, CH, MH, OH, CL-ML, and Pt. ❑FINE FRACTION: % passing through No. 200 sieve. ❑COARSE FRACTION: % retained on No. 200 sieve. ❑GRAVEL FRACTION: % retained on No. 4 sieve ❑SAND FRACTION: % retained on No. 200 - % passing on No. 4 sieve Prepared by: Gine O. G. (KSU-CEIT) UNIFIED SOIL CLASSIFICATION SYSTEM Source: Fundamentals of Geotechnical Engineering, 4th Edition by Braja M. Das  UNIFIED SOIL CLASSIFICATION SYSTEM Prepared by: Gine O. G. (KSU-CEIT) UNIFIED SOIL CLASSIFICATION SYSTEM UNIFIED SOIL CLASSIFICATION SYSTEM UNIFIED SOIL CLASSIFICATION SYSTEM Prepared by: Gine O. G. (KSU-CEIT) 𝑆𝑜𝑢𝑟𝑐𝑒: 𝐹𝑢𝑛𝑑𝑎𝑚𝑒𝑛𝑡𝑎𝑙𝑠 𝑜𝑓 𝐺𝑒𝑜𝑡𝑒𝑐ℎ𝑛𝑖𝑐𝑎𝑙 𝐸𝑛𝑔𝑖𝑛𝑒𝑒𝑟𝑖𝑛𝑔, 4𝑡ℎ 𝐸𝑑𝑖𝑡𝑖𝑜𝑛 𝑏𝑦 𝐵𝑟𝑎𝑗𝑎 𝑀. 𝐷𝑎𝑠 COMPARISON OF AASHTO AND USCS Both soil classification systems, AASHTO and Unified, are based on the texture and plasticity of soil. Also, both systems divide the soils into two major categories, coarse grained and fine grained, as separated by the No. 200 sieve. AASHTO USCS ✓ FINE GRAINED SOILS: ✓ FINE GRAINED SOILS: More than 35% passes More than 50% passes through the No. 200 sieve through the No. 200 sieve. ✓ No. 10 sieve is used to separate ✓ No. 4 sieve is used to separate gravel from sand gravel from sand ✓ The gravelly and Sandy soils ✓ The gravelly and Sandy soils are not separated. are clearly separated. ✓ Classification of organic soils is ✓ Classification of organic soils is not provided or indicated. provided. Prepared by: Gine O. G. (KSU-CEIT)  Sample Problem: Classify the following soils according to USCS SOIL % passing Sieve No. Dia. (mm) A B 4 4.75 70 10 2 100 40 0.425 80 200 0.075 58 30 Liquid Limit 0.250 30 33 Plasticity index 0.150 10 12 Prepared by: Gine O. G. (KSU-CEIT) Solution – SOIL A: Prepared by: Gine O. G. (KSU-CEIT) Solution – SOIL A: ✓GROUP SYMBOL : CL ✓GROUP NAME : SANDY LEAN CLAY Prepared by: Gine O. G. (KSU-CEIT) Solution – SOIL B:  Solution – SOIL B: ✓GROUP SYMBOL : SC ✓GROUP NAME : CLAYEY SAND WITH GRAVEL Prepared by: Gine O. G. (KSU-CEIT)  Sample Problem: Classify the following soils according to USCS SOIL A SOIL B Liquid Limit 35 20 Plastic Limit 27 15 % passing No. 200 11 82 % retained No. 4 10 0 Soil A have the ff: D10 = 0.09 mm ∶ D30 = 0.12 mm ∶ D60 = 0.14 mm Plasticity Index 8 5 Cu = D60/D10 1.556 Cc = D30^2 / (D60*D10) 1.142 SP-SC CL-ML Soil Classification Poorly graded sand with clay Sandy Silty Clay