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Lecture 4 classification of soil

Soil Mechanics

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Lecture 4 classification of soil

  1. 1. INTERNATIONAL UNIVERSITY FOR SCIENCE & TECHNOLOGY ‫وا‬ ‫م‬ ‫ا‬ ‫و‬ ‫ا‬ ‫ا‬ CIVIL ENGINEERING AND ENVIRONMENTAL DEPARTMENT 303322 - Soil Mechanics Classification of Soils Dr. Abdulmannan Orabi Lecture 2 Lecture 4
  2. 2. Dr. Abdulmannan Orabi IUST 2 Das, B., M. (2014), “ Principles of geotechnical Engineering ” Eighth Edition, CENGAGE Learning, ISBN-13: 978-0-495-41130-7. Knappett, J. A. and Craig R. F. (2012), “ Craig’s Soil Mechanics” Eighth Edition, Spon Press, ISBN: 978- 0-415-56125-9. References
  3. 3. A soil classification system- It is the arrangement of different soils with similar properties into groups & subgroups based on their application or to their probable engineering behavior. Introduction A classification for engineering purposes should be based mainly on mechanical properties: permeability, stiffness, strength. Dr. Abdulmannan Orabi IUST 3
  4. 4. Most of the soils classification systems that have been developed for engineering purposes are based on simple index properties such as particle size distribution & plasticity. Introduction The aim of a classification system is to establish a set of conditions which will allow useful comparisons to be made between different soils. Dr. Abdulmannan Orabi IUST 4
  5. 5. Classification System SOIL CLASSIFICATION BASICS Commonly based on grain size and soil consistency. Several classification systems exist: 1. Unified Soil Classification System (USCS) (ASTM D2487-11). 2. American Association of State Highway and Transportation Officials (AASHTO) (ASTM D3282-09). Dr. Abdulmannan Orabi IUST 5
  6. 6. Unified Soil Classification System (USCS) According to the USCS, the soils are divided into two major categories: 1. Coarse-grained soil that are gravelly and sandy in nature with less than 50 % passing through the No 200 sieve ( that is F200 < 50%). 2. Fine-grained soils with 50% or more passing through the No. 200 sieve ( that is F 200 > 50%). Dr. Abdulmannan Orabi IUST 6
  7. 7. •The soil is classified into 15 groups. • Each group is designated a symbol consisting of two capital letters. •The first letter is based on main soil type. •The second letter is based on gradation and plasticity . Unified Soil Classification System (USCS) Dr. Abdulmannan Orabi IUST 7
  8. 8. Unified Soil Classification System (USCS) The following Symbols are used in this system: 1. Coarse-grained P – Poorly graded W–Well graded M – Silty C – Clayey G – Gravel S – Sand 2. Fine-grained soil M – Silt, C – Clay, O – Organic L – Low Plastic H – High Plastic First Letter Second Letter Dr. Abdulmannan Orabi IUST 8
  9. 9. Group Symbol Typical Name Sw or Gw Well graded soil (sand or gravel ) SP or GP Poorly graded soil ( sand or gravel ) GM Silty gravel or Silty gravel with sand GC Clayey gravel or Clayey gravel with sand SM Silty sand or Silty sand with gravel SC Clayey sand or Clayey sand with gravel Unified Soil Classification System (USCS) 1. Coarse-grained Dr. Abdulmannan Orabi IUST 9
  10. 10. Unified Soil Classification System (USCS) Group Symbol Typical Name CL Inorganic clays of low plasticity. ML Inorganic silts with slight plasticity. OL Organic soil of low plasticity. CH Inorganic clays of high plasticity. MH Inorganic silts with high plasticity. OH Organic soil of high plasticity. Pt Peat. 2. Fine-grained soil Dr. Abdulmannan Orabi IUST 10
  11. 11. Unified Soil Classification System (USCS) The classification is based on material passing a 75mm sieve: Coarse–grainedSoil Fine– grained SoilR 200 > 50 F200 > 50 Gravel Sand Silt & Clay Sieve No. 4 Sieve No. 200 F200 R200 F4 R4 4.75 mm 0.075 mm Dr. Abdulmannan Orabi IUST 11
  12. 12. Unified Soil Classification System (USCS) F 200 = percent passing No. 200 sieve ( % of fines ) R4 = percent retained above No.4 sieve. ( % of Gravel ) R200 = percent retained above No.200 sieve. F4 = percent passing No. 4 sieve Dr. Abdulmannan Orabi IUST 12
  13. 13. Worked Example F200 = 14% R4 = 18 % R200 = 86% F4 = 82% Gravel = 18 % Sand = 68 % Silt and Clay= 14% Gravel Sand Silt & Clay Sieve No. 4 Sieve No. 200 F200 R200 F4 R4 4.75 mm 0.075 mm Dr. Abdulmannan Orabi IUST 13
  14. 14. Unified Soil Classification System (USCS) If R4/ R200 > 0.5, the soil is a gravel ( G ) 1. Coarse-grained soil Symbol Criteria GW F200<5 % Cu > 4 , 1< Cc < 3 GP F200<5 % Not meeting the GW criteria of Cu & Cc GM F200>12 % PI < 4, or plots below A-Line ( Plasticity Chart ) GC F200>12 % PI > 7, and plots on or above A-Line GW-GM 5<F200<12 Satisfies Cu & Cc crit. of GW, meets PI for GM GW-GC 5<F200<12 Satisfies Cu & Cc crit. of GW, meets PI for GC GP-GM 5<F200<12 Doesn't satisfy Cu & Cc crit, of GP, meets PI,GM GP-GC 5<F200<12 Doesn't satisfy Cu & Cc crit, of GP, meets PI,GM GM-GC F200>12 % PI plots in the hatched area ( Plasticity Chart ) Dr. Abdulmannan Orabi IUST 14
  15. 15. Unified Soil Classification System (USCS) Symbol Criteria SW F200<5 % Cu > 6 , 1< Cc < 3 SP F200<5 % Not meeting the GW criteria of Cu & Cc SM F200>12 % PI < 4, or plots below A-Line ( Plasticity Chart ) SC F200>12 % PI > 7, and plots on or above A-Line SW-SM 5<F200<12 Satisfies Cu & Cc crit. of SW, meets PI for SM SW-SC 5<F200<12 Satisfies Cu & Cc crit. of SW, meets PI for SC SP-SM 5<F200<12 Doesn't satisfy Cu & Cc crit, of SP, meets PI,SM SP-SC 5<F200<12 Doesn't satisfy Cu & Cc crit, of SP, meets PI,SM SM-SC F200>12 % PI plots in the hatched area ( Plasticity Chart ) 1. Coarse-grained soil If R4/ R200 > 0.5, the soil is a gravel ( G ) Dr. Abdulmannan Orabi IUST 15
  16. 16. Unified Soil Classification System (USCS) 2. Fine – Grained Soil Silts and Clays: LL < 50 % ML PI < 4 or plots below A- Line CL PI > 7 and plots on or above A –Line CL- ML PI plots in the hatched area OL PI plots in the OL area Dr. Abdulmannan Orabi IUST 16
  17. 17. Unified Soil Classification System (USCS) 2. Fine – Grained Soil Silts and Clays: LL > 50 % MH PI plots above A- Line CH PI plots on or above A –Line OH plots in the OH area Pt High organic matter (Peat) Dr. Abdulmannan Orabi IUST 17
  18. 18. Unified Soil Classification System (USCS) 0 10 20 30 40 50 60 70 0 10 20 30 40 50 60 70 80 90 100 CH or OH LL PI MH or OH CL or ML or OL CL - ML Liquid Limit ( % ) PlasticityIndex OL Plasticity Chart Dr. Abdulmannan Orabi IUST 18
  19. 19. Unified Soil Classification System (USCS) Plasticity Chart Note: If the results of your soil tests fall above the U – line on the plasticity chart, you should be suspicious of your results and repeat your tests. Dr. Abdulmannan Orabi IUST 19
  20. 20. Example 1 Unified Soil Classification System (USCS) Using the grain-size distribution curve shown below, determine the uniformity coefficient Cu and classify the soil Particle diameter (mm) Percentfiner #10 #200#60 10 20 30 40 100 0 0.01110 50 60 70 80 90 D30 D10D60 Dr. Abdulmannan Orabi IUST 20
  21. 21. Unified Soil Classification System (USCS) Solution From the grain distribution curve, D60 = 0.60 mm, D30 = 0.20 mm and D10 = 0.09 mm, F200= 0, R4= 3 therefore the coefficients are, A well-graded soil has a uniformity coefficient greater than 4 for gravels and 6 for sands. Therefore, this soil is classified as uniform sand. (According USCS, the soil is SP ). = = 0.6 0.09 = 6.67 = ∗ = 0.74 Dr. Abdulmannan Orabi IUST 21
  22. 22. Unified Soil Classification System (USCS) Example 2 Laboratory tests were performed on a light-brown sandy soil, which visually has several pieces of gravel larger than 6 mm, indicated that PL = 22.6 % and LL = 33.2 %. Classify this soil using USCS. Sieve No. % Passing 4 98.0 40 36.5 200 28.5 Dr. Abdulmannan Orabi IUST 22
  23. 23. Unified Soil Classification System (USCS) Solution F200 = 28.5% < 50% , the soil is coarse grained. R4 = 2%, R4/R200 < 0.5, the soil is sand F200 = 28.5% > 12% The soil group is SM or SC PI = 33.2 – 22.6 = 10.6% Atterberg limits above A-Line Therefore, this soil can be classified as SC Dr. Abdulmannan Orabi IUST 23
  24. 24. AASHTO Classification System The classification system is based on the following criteria 1. Grain size a. Gravel: fraction passing the 75 mm sieve and retained on the No. 10 ( 2mm ) sieve b. Sand: fraction passing the No. 10 sieve and retained on the No. 200 U.S. sieve. c. Silt and clay: fraction passing No.200sieve. Dr. Abdulmannan Orabi IUST 24
  25. 25. AASHTO Classification System 2. Plasticity : the term silty is applied when the fine frictions of the soil have a plasticity index of 10 or less. The term clayey is applied when the fine frictions have a plasticity index of 11or more. 3. If cobbles and boulders are encountered, they are excluded form the portion of the soil sample which classification is made. Dr. Abdulmannan Orabi IUST 25
  26. 26. According to the present form of this system, soils can be classified according to eight major groups, A-1 through A-8, based on their grain size distribution, liquid limit, and plasticity indices. AASHTO Classification System Dr. Abdulmannan Orabi IUST 26
  27. 27. Soils listed in groups A-1, A-2, and A-3 are coarse-grained materials, and those in groups A-4, A-5, A-6, and A-7 are fine-grained materials. Peat, muck, and other highly organic soils are classified under A-8. They are identified by visual inspection. AASHTO Classification System Dr. Abdulmannan Orabi IUST 27
  28. 28. AASHTO Classification System According to the AASHTO, the soils are divided into two major categories: 1. Coarse-grained soil that are gravelly and sandy in nature with less than 35 % passing through the No 200 sieve ( that is F200 < 35%). 2. Fine-grained soils with 35% or more passing through the No. 200 sieve ( that is F 200 > 35%). Dr. Abdulmannan Orabi IUST 28
  29. 29. AASHTO Classification System Granular materials ( F200 < 35% ) Group classification A – 1 A - 3 A – 1 – a A – 1 – b Sieve analysis (Percentage passing ) No. 10 50 max No.40 30 max 50 max 51 min No.200 15 max 25 max 10 max Characteristic of fraction passing No. 40 Liquid Limit ------ Plasticity index 6 max NP Usual types of materials Stone fragments, gravel, and sand Fine sand Dr. Abdulmannan Orabi IUST 29
  30. 30. AASHTO Classification System Granular materials ( F200 < 35% ) Group classification A - 2 A – 2 – 4 A – 2 –5 A – 2 - 6 A – 2 - 7 Sieve analysis (Percentage passing ) No. 10 No.40 No.200 35 max 35 max 35 max 35 max Characteristic of fraction passing No. 40 Liquid Limit 40 max 41 min 40 max 41 min Plasticity index 10 max 10 max 11 min 11 min Usual types of materials Silty or clayey gravel and sand Dr. Abdulmannan Orabi IUST 30
  31. 31. AASHTO Classification System Plasticity Chart 0 10 20 30 40 50 60 70 0 10 20 30 40 50 60 70 80 90 100 A-4A-2-4 A-7-6 A-2-5A-5 A-2-7 A-7-5 A-2-6 A-6 Liquid Limit, LL PlasticityIndex,PI PI< LL – 30 PI>LL – 30 Dr. Abdulmannan Orabi IUST 31
  32. 32. AASHTO Classification System Group Index ( GI ) To evaluate the quality of a soil as a highway subgrade material, one must also incorporate a number called the group index (GI) with the groups and subgroups of the soil. Group index of a soil depends on amount of material passing 75 micron IS sieve, liquid limit , and plastic limit. Dr. Abdulmannan Orabi IUST 32
  33. 33. AASHTO Classification System Group Index ( GI ) 1. Used to describe performance of soil when used for pavement construction. 2. Note used to place a soil in a particular group 3. It means rating the value of soil as a subgrade material within its own group 4. Higher the value of GI, poorer is the quality of material. The quality of performance of a soil as a subgrade material is inversely proportional to GI. Dr. Abdulmannan Orabi IUST 33
  34. 34. AASHTO Classification System Group Index ( GI ) The group index is given by the equation: GI = (F200-35)[0.2+0.005(LL-40)]+0.01(F200-15)(PI-10) When calculating the group index for soils that belong to group A – 2 – 6 and A – 2 – 7 , use the partial group index for PI, or GI = 0.01(F200 -15) (PI - 10) Dr. Abdulmannan Orabi IUST 34
  35. 35. AASHTO Classification System A soil having GI of zero is considered as the best. If the equation gives negative value for GI, consider it zero. Always round off the GI to nearest whole number. GI=0 for soils of groups A-1-a, A-1-b ,A-2-4, A-2-5, and A-3. Group Index ( GI ) There is no upper limit for the group index Dr. Abdulmannan Orabi IUST 35
  36. 36. The results of the particle-size analysis of a soil are as follows: Percent passing through the No. 10 sieve = 100 Percent passing through the No. 40 sieve = 80 Percent passing through the No. 200 sieve = 58 The liquid limit and plasticity index are 30 and 10, respectively. Classify the soil by the AASHTO system. Worked Examples Example 3 Dr. Abdulmannan Orabi IUST 36
  37. 37. F200 = 58% > 35%, the soil is fine- grained ( silt or clay ) Using plasticity chart(slid No. 24), the soil is A-4. So, the soil will be classified as A-4 (3) Worked Examples Solution GI = (F200-35)[0.2+0.005(LL-40)]+0.01(F200-15)(PI-10) GI = (58-35)[0.2+0.005(30-40)]+0 .01(58-15)(10-10) GI = 3.45 Dr. Abdulmannan Orabi IUST 37
  38. 38. Worked Examples Example 4 Ninety-five percent of a soil passes through the No. 200 sieve and has a liquid limit of 60%and plasticity index of 40. Classify the soil by the AASHTO system. Solution : F200 = 95% > 35 According to plasticity chart, this soil falls under group A-7 , 40 > 60 – 30, GI = 42 The soil is A-7 – 6 ( 42 ) Dr. Abdulmannan Orabi IUST 38
  39. 39. For an inorganic soil, the following grain-size analysis is given: For this soil, LL = 23% and PL = 19%. Classify the soil according to: a. the AASHTO soil classification b. the Unified soil classification system Worked Examples Example 5 Sieve No. % Passing 4 100 10 90 20 64 40 38 80 18 200 13 Dr. Abdulmannan Orabi IUST 39
  40. 40. Classify the following soils using Unified classification system Worked Examples Example 6 Soil Sieve analysis, Liquid Limit Plasticity indexNo.4 No.200 A 80 52 30 8 B 79 45 26 4 C 91 80 60 32 D 95 75 41 12 E 82 41 24 2 Dr. Abdulmannan Orabi IUST 40
  41. 41. Worked Examples Example 6 Classify the following soils using USCS and AASHTO systems and give the GI. Soil Sieve analysis, LL PI No.4 No. 10 No. 20 No. 40 No. 60 No. 100 No. 200 0.01 mm 0.002 mm A 94 63 21 10 7 5 3 - - - NP B 98 86 50 28 18 14 10 - - - NP C 100 100 98 93 88 83 77 65 60 63 25 D 100 100 100 99 95 90 86 42 40 55 28 E 100 100 100 94 82 66 45 26 21 36 22 Dr. Abdulmannan Orabi IUST 41
  42. 42. 0 10 20 30 40 50 60 70 80 90 100 0.010.1110 Worked Examples Curve – soil A Example 6 Dr. Abdulmannan Orabi IUST 42
  43. 43. Classify the following soils using the AASHTO system and give the GI. Worked Examples Example 7 Soil Sieve analysis, LL PI No. 10 No. 40 No. 200 A 62 30 8 - NP B 90 67 35 32 8 C 90 76 34 37 12 D 100 78 8 - NP E 85 68 45 38 9 Dr. Abdulmannan Orabi IUST 43

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