SOIL FORMATION SOIL CLASSIFICATION FOR GEOTECHNICAL ENGINEERS. Soil Properties and Classification

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SOIL CLASSIFICATION FOR GEOTECHNICAL ENGINEERS Soil Properties and Classification Soil Formation

classification of soils Physical Properties of Soils Engineering use of soils.

soil formation Physical and Chemical Weathering Weathering (+ Biological) Residual or Transported

1 SOIL CLASSIFICATION FOR GEOTECHNICAL ENGINEERS Soil Properties and Classification Soil Formation Soil Types Particle Size Analysis and Grading Characteristics Consistency Indices Engineering classification of soils Physical Properties of Soils Engineering use of soils. SOIL FORMATION What is the main difference between soil and rock Geological Processes active in soil formation Physical and Chemical Weathering Weathering (+ Biological) Residual or Transported Importance of Mode of Transportation Gravity, Wind, Water, Ice. Particle Size, Shape, Sorting, packing RESIDUAL SOIL GRANITE

2 HONG KONG VOLCANICS WIND RESIDUAL VOLCANIC SOIL GRAVITY GLACIAL TILL OUTWASH SANDS AND GRAVELS

PARTICLE SHAPE SOIL TYPES Soil Type Term Field test Sands, gravels Loose Can be excavated with a spade; 5mm wooden peg can be easily

lumps which can be abraded Silts Soft or loose Easily moulded or crushed in the fingers.

hand Soft Firm Stiff Very stiff Moulded by light finger pressure Can be moulded by strong finger pressure Cannot be indented by the

3 PARTICLE SHAPE SOIL TYPES Soil Type Term Field test Sands, gravels Loose Can be excavated with a spade; 5mm wooden peg can be easily driven Dense Slightly cemented Requires a pick for excavation; 5mm wooden peg is hard to drive Visual examination; pick removes soil in lumps which can be abraded Silts Soft or loose Easily moulded or crushed in the fingers. Firm or dense Can be moulded or crushed by strong pressure in the fingers Clays Very soft Exudes between the fingers when squeezed in the hand Soft Firm Stiff Very stiff Moulded by light finger pressure Can be moulded by strong finger pressure Cannot be indented by the thumbnail Can be indented by the thumbnail Organic,Peat Firm Fibres already compressed together Spongy Plastic Very compressible and open structure Can be moulded in the hand and smears the fingers

4 IMPORTANT CLAY MINERALS Mineral name Kaolinite Structure G G Between layers H-bond linkage Approx. size (µm) l =.2-2. t=.5-.2 Specific Approx. exchange surface( capacity m 2 /g) (me/1g) Halloysite G G H 2 O tubular l =.5 t= CLAY MINERALS Illite G K K G G G K + linkage Montmorillonite Weak crosslinkage between Mg/Al ions l =.2-2. t=.1-.1 l =.1-.5 t= Structure and its engineering importance Vermiculite Mg Mg 2+ linkage l = t= THE THREE MOST IMPORTANT CLAY MINERALS Kaolinite Illite Montmorillonite Problems Single sheet of silica tetrahedra (T) combined with single sheet of alumina octahedra (O). Sheets of alumina octahedrons between and combined with two silica tetrahedrons. (TOT:TOT) Same basic structure as illite. Very limited isomorphous substitution Substitution of Al by Mg and Iron in Octahedral sheet and partial substitution of Silicon by Al in tetrahedral sheet. Partial substitution of Al by Mg in the octahedral sheet. Water molecules and (exchangeable) cations other than potassium present in space between combined TOT sheets. KAOLINITE ILLITE MONTMORILLONITE TO:TO sheets held fairly tightly together by hydrogen bonding (1 particle = 1+ stacks). Absorb little water. Low swelling and shrinkage potential, Combined TOT:TOT sheets held together by fairly weak bonding due to potassium ions. Absorb more water than kaolinites and have higher swelling/shrinkage potential. Very weak bond between combined TOT sheets due to these ions. Extremely high water absorption between TOT sheets, swelling and shrinkage potential.

5 Clay Structure PARTICLE SIZE ANALYSIS a) Undisturbed Salt water deposit b) Undisturbed Fresh water deposit Coarse Grained soils Sieve Analysis Fine Grained soils Hydrometer method Grading Characteristics c) Remoulded Boulders (>35mm or >12in) Cobbles 75-35mm or 3-12in))

6 45mm Coarse sand Coarse gravel Medium sand Fine gravel Fine sand Hydrometer Size Analysis

$6.2.6.2.6.2.6 2 6 2 2 f m c f m c f m c Clay Silt fraction Sand fraction gravel fraction stone Particle size (mm) Percentage finer 1 8 Silty Clay 4 2.2.6.2.6.2.6 2 6 2 mm F M C M Clay F C F M C Silt$

7 PARTICLE SIZE DISTRIBUTION PARTICLE SIZE DISTRIBUTION CURVE Percentage passing f m c f m c f m c Clay Silt fraction Sand fraction gravel fraction stone Particle size (mm) Percentage finer 1 8 Silty Clay mm F M C M Clay F C F M C Silt Sand Gravel SandySilt Very Sandy Silt Well Graded Sand Well Graded Gravel USCS PARTICLE SIZE RANGES Sieve Identification Opening Size (in) Opening Size (mm) 3in CG Sieve Size Particle Diameter 2in CG Passes Retained on (in) (mm) Soil Classification 12in >12 >35 Boulder Rock 12in 3in Cobble Fragments 3in 3/4in Coarse gravel Soil 3/4in # Fine gravel #4 # Coarse sand #1 # Medium sand #4 # Fine sand #2 <.29 <.75 Fines (silt + clay) 1 1/ CG CG ¾ CG 3/ FG # FG # CS # CS # MS # MS # MS # MS # FS # FS # FS # FS # S & C STANDARD SIEVE SIZES USED IN UNIFIED SOIL CLASSIFICATION SYSTEM

% passing by weight 1 9 8 7 5 4 3 2 1 FINES #2 PARTICLE SIZE DISTRIBUTION.1.1.1 1 1 1 Log grain size (mm) SAND #4 GRAVEL 76.2 Well Graded wide range of particle sizes.

8 % passing by weight FINES #2 PARTICLE SIZE DISTRIBUTION Log grain size (mm) SAND #4 GRAVEL 76.2 Well Graded wide range of particle sizes. (Fine sand to Coarse gravel) Soil A Soil B Soil C Poorly Graded narrow range of particle sizes. (Pea gravel) SIGNIFICANCE OF GRAIN SIZE DISTRIBUTION PARTICLL SIZE CURVE: GRADING COEFFICIENTS CG Soils Well Graded Mixtures (poorly sorted) More stable Less Compressible Less Permeable > 1% Clay - dominates permeability > 3% Clay - dominates strength % Finer grading curve d 1 d 3 d Particle Size (mm) Coefficient of Uniformity D C U = D 1 Coefficient of Curvature 2 D 3 C Z = D D 1

9 Consistency Indices Consistency indices (Atterberg Limits) Clays and silts are characterized by the variation in behavior with change in water content Particularly important is their plastic behavior. Total Soil Volume V d V a V s Natural water content Solid Semiplastic solid Plasticity Index (PI) Plastic Liquid w s w p w L % Water Content w PL LI = = Liquidity Index PI

10 THE PLASTIC LIMIT TEST PI% >35 Volume change potential(swelling/ Shrinkage) Very High SOIL PROPERTIES IMPORTANT IN SUMO WRESTLING? <18 High Medium Low THE LIQUID LIMT TEST Casagrande grooving tool Brass cup 1mm gauge for checking height of fall of cup Remoulded soil sample LIQUID LIMIT TEST (1) Height of fall of cup Hard rubber base

11 Sieve Analysis Wc 1 LIQUID LIMIT (2): CONE PENETRATION Log. No.Blows 55mm 3 o Cone 3 Part of soil used for hydrometer analysis Casagrande Cup 2 Repeat test several times at different water contents LIQUID LIMIT DETERMINATION USING THE CONE PENETRATION TEST Linear Shrinkage and Shrinkage Limit Cone Penetration (mm) LL = 55% 5 55 Moisture Content (%)

12 SOIL CLASSIFICATION AND CONSISTENCY INDICES (ASTM) PLASTICIY INDEX (LL-PL) % 4 2 CL-ML 2 CL ML or OL 4 CH MH or OH LIQUID LIMIT % PI=.73(LL-2) A-LINE SOIL CLASSIFICATION AND CONSISTENCY INDICES PLASTICIY INDEX (LL-PL) % 4 2 Plasticity Low Int. High V. high Ext. high CV CE CL CI CH MH MV ML MI LIQUID LIMIT % ME A-LINE PLASTICITY OF SOILS Class PI% < >35 Description Non Plastic Slightly Plastic Mod Plastic Highly Plastic Extremely Plastic

13 TYPICAL ATTERBERG LIMITS FOR SOILS Plasticity according to Liquid Limit Soil Type Sand W LL % N o n W PL % P la s I p % t i c Description Lean or Silty Intermediate Plasticity Low Intermediate Range of LL < Silt Fat Very Fat High Very High Clay Extra Fat Extra High >9 Shine TEST Grittiness Toughness Dry strength Shaking (Dilatancy) Silts and Clays METHOD Rub particles between fingers or taste Take pat of soil, moist enough to be plastic but not sticky and roll it to a thread 3mm in size in your palm. Fold and reroll thread repeatedly until it crumbles. Lump pieces together and knead to measure toughness Stroke soil with a blade Allow soil to dry then squeeze Squeeze a moistened sample, open hand, then shake or tap your hand Soil crumbles high silt content Dull SILT Gritty texture Powders Moisture film comes to surface, glistens CLAY Smooth texture Soil is tough or stiff high clay content Shiny Hard to break No moisture film Fine Sand Individual partciles visible Exhibits dilatancy Easy to crumble and falls off hands when dry Feels gritty No plasticity IN THE FIELD Silt Some particles visible Exhibits dilatancy Easy to crumble and can be dusted off hands when dry Feels rough Some Plasticity Clay No particles visible No dilatancy Hard to crumble and sticks to hands when dry Feels smooth Plasticity

14 SOIL CLASSIFICATION AASHTO SYSTEM Used in highways 7 major groups 8 subgroups Soil designated using Group/subgroup and a group index (GI) UNIFIED SOIL CLASSIFICATION SYSTEM Most common in North America Soils divided into coarse/fine based on grain size Coarse soils divided into gravels and sands Full designation based on grading(well/poor using C u and C c ) and percentage of fines Fine soils divided into inorganic silts and clays based on use of Casagrande chart (PI and LL) Peat treated as separate soil type. Table 1. AASHTO Classification for Coarse-Grained Soils Soil Group (1) A-1 A-1-a 5max. A-1-b A-3 A-2-4 A-2-5 A-2 A-2-6 A-2-7 Grain size Liquid Plasticity Material Subgrade Passing Passing Passing rating Limit* Index* type #1 sieve #4 sieve #2 sieve (2) (3) (4) (5) (6) (7) (8) 3max. 5max. 51min. 15max. 25max. 1max. 35max. 35max. 35max. 35max. 4max. 41min. 4max. 41min. 6max. 6max. Nonplastic 1max. 1max. 11min. 11min. Stone fragments, gravel and sand Fine sand Silty and clayey gravel and sand Excellent to good * Based on fraction passing #4 sieve Soil Group (1) A-4 A-5 A-6 A-7 Table 2. AASHTO Classification for Fine-Grained Soils A-7-5 A-7-6 Passing #2 sieve (2) 36min 36min 36min 36min 36min LL* (3) 4max. 41min 4max. 41min 41min * Based on fraction passing #4 sieve PI* (4) 1max. 1max. 11min 11min and PL<=LL-3 11min and PI>LL-3 Material type (5) Silty soil Silty soil Clayey soil Clayey soil Clayey soil Subgrade rating (6) Fair to poor Fair to poor Fair to poor Fair to poor Fair to poor Plasticity Index % Liquid Limit and Plasticity Index for 9 AASHTO Soil Groups A-6 A-2-6 A-7-6 A-7-5 A A-4 A-5 A-2-4 A Liquid Limit %

15 AASHTO PROCEDURE %Passing Soil A Soil B # # # # LL PL PI Group/ Subgroup A-2-6 A-7-6 From Table 1 GI Name A-2-6() 1 A-7-6(1) UNIFIED SOIL CLASSIFICATION Subdivides soil based on the % passing No. 2 sieve into Coarse grained Fine grained Coarse grained soils subdivided into Gravels and Sands based on % passing No. 4 sieve. (% of fines (passing No 2 sieve) is use to further describe coarse grained soils.) Coarse grained Fine grained <35% >35% GI=.1(F2-15)(PI- 1) =.1(34-15)(12-1)=.38 ~ From Table 2 GI = (F2-35)[.2 +.5(LL-4)] + (.1(F2-15)(PI-1) = (58-35)[.2 +.5(49-4)] +.1(58-15)(21-1) = 1.37 ~1 Fine grained soils are subdivided into Inorganic and Organic Inorganic and Organic clays are subdivided in to silts and clays of high and low plasticity using the a plasticity chart (% of coarse-grained sand or gravel used to further describe silts and clays) Following Tables show detailed breakdown of the USC which will be used in lab exercise UNIFIED SOIL CLASSIFICATION: FINE GRAINED SOILS: LL 5 Criteria for Group Group Symbol Symbol LL 5 and PI.73(LL-2) LL 5 and PI<.73(LL-2) CH MH Criteria for Group Name R 2 SF/GF GF SF Group Name Fat clay 15 1 Fat clay with sand to 29 <1 Fat clay with gravel 3 15 to <1 <1 1 <1 1 1 <1 <1 Sandy fat clay Sandy fat clay with gravel Gravelly fat clay Gravelly fat clay with sand Elastic silt Elastic silt with sand Elastic silt with gravel Sandy elastic silt Sandy elastic silt with gravel Gravelly elastic silt Gravelly elastic silt with sand

16 UNIFIED SOIL CLASSIFICATION: GRAVELLY SOILS: R 4 >.5R 2 UNIFIED SOIL CLASSIFICATION: SANDY SOILS: R 4.5R 2 F 2 <5 >12 5 F 2 12 Criteria for Group Symbol C u C c 4 1 C c 3 Relation between LL and PI 4 1 C c 3 C u <4 and/or 1>C c >3 PI<4 or PI<.73(LL-2) PI>7 and PI.73(LL-2) 4 PI 7 and PI.73(LL-2) PI<4 or C u <4 and/or 1>C c >3 PI<.73(LL-2) PI>7 and PI.73(LL-2) PI<4 or PI<.73(LL-2) PI>7 and PI.73(LL-2) Criteria for Group Group Name Group Name Symbol SF GW Well graded gravel with sand Well graded gravel GP Poorly graded gravel Poorly graded gravel with sand GM Silty gravel Silty gravel with sand GC Clayey gravel Clayey gravel with sand GC-GM Silty, clayey gravel Silty, clayey gravel with sand GW-GM Well graded gravel with silt Well graded gravel with silt and sand Well graded gravel with clay GW-GC Well graded gravel with clay and sand GP-GM Poorly graded gravel with silt Poorly graded gravel with silt and sand GP-GC Poorly graded gravel with clay Poorly graded gravel with clay and sand F 2 <5 >12 5 F 2 12 Criteria for Group Symbol C u C c 6 1 C c 3 Relation between LL and PI 6 1 C c 3 C u <6 and/or 1>C c >3 PI<4 or PI<.73(LL-2) PI>7 and PI.73(LL-2) 4 PI 7 and PI.73(LL-2) PI<4 or C u <6 and/or 1>C c >3 PI<.73(LL-2) PI>7 and PI.73(LL-2) PI<4 or PI<.73(LL-2) PI>7 and PI.73(LL-2) Group Symbol SW SP SM SC SC-SM SW-SM SW-SC SP-SM SP-SC Criteria for Group Name Group Name GF Poorly graded sand Well graded sand Well graded sand with gravel Poorly graded sand with gravel Silty sand Silty sand with gravel Clayey sand Clayey sand with gravel Silty, clayey sand Silty, clayey sand with gravel Well graded sand with silt Well graded sand with silt & gravel Well graded sand with clay Well graded sand with clay & gravel Poorly graded sand with silt Poorly graded sand with silt and gravel Poorly graded sand with clay Poorly graded sand with clay and gravel SENSITIVITY OF SOILS

Solution:Example 1. Example 2. Solution: Example 2. clay. Textural Soil Classification System (USDA) CE353 Soil Mechanics Dr.

Solution:Example 1. Example 2. Solution: Example 2. clay. Textural Soil Classification System (USDA) CE353 Soil Mechanics Dr. CE353 Soil Mechanics CE353 Lecture 5 Geotechnical Engineering Laboratory SOIL CLASSIFICATION Lecture 5 SOIL CLASSIFICATION Dr. Talat A Bader Dr. Talat Bader 2 Requirements of a soil Systems Why do we need