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14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
SO, THIS PICTURE KEEPS POPPINGINTO MY TIMELINE…
A Philosophy Professor stood before his class…
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14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
Jar = Your LifeGolf Balls = Important Things” (e.g. Family)
Pebbles = “Things that Matter” (e.g. job, house,
car, etc.)Sand = Everything Else
(“Small Stuff”)Beer: Always room for a
beer with Friends.
Why is a Philosophy Professor talking to a
Math Class?
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14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
SOIL COMPOSITION BASICS
Soil is comprised of3 Major
Components
1. Soil Particles (S)2. Water (W)3. Air (A) (if not
saturated)Typical Soil Matrix
Slide 1 of 11
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3 PHASE DIAGRAMSOIL MATRIX
Figure 2-1. from FHWA NHI-06-088.
Soil Particles
Voids (filled with
water and air)
Solid
Water
Air Va
Vw
Vs
Wa 0
Ww
Ws
Vv
V W
Volume Weight
1 unit
SOIL COMPOSITION BASICS
Slide 2 of 11
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Main Variables:V = VolumeW = Weightm = Mass
Subscripts:a = airv = voidsw = waters = solidst = total (or
blank)
Solid
Water
Air Va
Vw
Vs
Wa 0
Ww
Ws
Vv
V W
Volume Weight
1 unit
Examples: Vs = Volume of SoilV = Vt = Total Volume
Figure 2-1. from FHWA NHI-06-088.
3 PHASE DIAGRAM
Slide 3 of 11
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Void Ratio (e) (given in decimal):
Porosity (n) (given in decimal or %):
e Volume of Voids(Vv )Volume of Solids(Vs )
n Volume of Voids(Vv )Total Volume (Vt )
e1 e
Figure 3.1. Das FGE (2005).
Dr emax eemax emin
Relative Density (given in %):
KEY RELATIONSHIPS:VOLUME
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Table 3.3. Das FGE (2005).
Where:Dr = Relative Density (%)e = Insitu Void Ratioemax = Maximum Void Ratioemin = Minimum Void Ratio
Used as an indication of the in-situ denseness or looseness.
Relative Density(Dr) (%)
Description of Soil Deposit
0 – 15 Very Loose15 – 50 Loose50 – 70 Medium70 – 85 Dense85 - 100 Very Dense
Dr emax eemax emin
KEY RELATIONSHIPS:RELATIVE DENSITY (DR)
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Figure 3.1. Das FGE (2005).
Moist Unit Weight (or t)(i.e. the soil “as is”):
t Weight (W)Volume (V)
Ww Ws
V
Degree of Saturation (S) (%):
S Vw
Vv
100%
Moisture Content (w):
s
w
WWw
KEY RELATIONSHIPS:WEIGHT-VOLUME
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Figure 3.1. Das FGE (2005).
Dry Unit Weight (d) (i.e. no water):
d Weight of Solids (Ws)Volume (V)
1 w
Gs s
w
Specific Gravity of Solids (Gs):
sat Ws Ww
V
(Gs e)w
1 e
Saturated Unit Weight (sat) (i.e. no air):
For Clays and Silts, 2.6 < Gs < 2.9For Quartz Sands: Gs ≈ 2.65
KEY RELATIONSHIPS:WEIGHT-VOLUME
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Modified after Table 2-1, FHWA NHI-06-088.
Property Symbol Units Obtained via: Comments & DirectApplications
Porosity n Dim Weight-Volume Relationships
Defines relative volume of voids to total soil volume.
Void Ratio e Dim Weight-Volume Relationships
Volume Change Calculations (Consolidation)
Moisture Content w Dim Measurement (D2216)
Classification and in weight-volume relations.
Compaction.
Total Unit Weight t F/L3
Weight-Volume Relationships or Measurement
Classification, Stress Computations, Compaction.
Specific Gravity Gs Dim By Measurement (D854) Volume computations.
Compaction.
KEY RELATIONSHIPS:INDEX PROPERTIES SUMMARY & APPLICATIONS
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Table 3.1. Das FGE (2005).
KEY RELATIONSHIPS:INDEX PROPERTIES SUMMARY & APPLICATIONS
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Where:
S = Degree of Saturatione = Void Ratiow = Moisture ContentGs = Specific Gravity of Solids
Figure 3.1. Das FGE (2005).
Se wGs
KEY EQUATION OFSOIL COMPOSITION
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TYPICAL SOIL PROPERTIES FOR SOILS IN A NATURAL STATE(AFTER TABLE 3.2, DAS FGE (2005)).
SoilVoid Ratio
(e)w
(%)d
(lb/ft3)
Loose Uniform Sand 0.8 30 92
Dense Uniform Sand 0.45 16 115
Loose Angular Silty Sand 0.65 25 102
Dense Angular Silty Sand 0.4 15 121
Stiff Clay 0.6 21 108
Soft Clay 0.9 - 1.4 30-50 73-93
Soft Organic Clay 2.5 – 3.2 90-120 38-51
Till 0.3 10 134Slide 11 of 11
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14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
SOIL CLASSIFICATION BASICSCommonly 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 Highwayand Transportation Officials (AASHTO)(ASTM D3282-09).
3. U.S. Department of Agriculture (USDA).4. Burmister Soil Identification System.5. Massachusetts Institute of Technology (MIT).
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14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
Soil Type USCS Symbol
Grain Size Range (mm)
USCS AASHTO USDA MIT
Gravel G 76.2 to 4.75 76.2 to 2 >2 >2
Sand S4.75 to0.075
2 to 0.075 2 to 0.05 2 to 0.06
Silt M Fines < 0.075
0.075to 0.002
0.05 to 0.002
0.06 to 0.002
Clay C < 0.002 < 0.002 < 0.002
Determined by Mechanical Analysis (i.e. Sieve) and Hydrometer Analysis(ASTM D422-63 (2007) Standard Test Method for Particle-Size Analysis of Soils)
SOIL GRAIN SIZES
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Figure 7.1. from FHWA NHI-01-031.
MediumGravelFine
GravelMedium-Coarse
SandSiltDry Clay(kaolin)
3/8 in#10#40
#200
MECHANICAL SIEVE ANALYSIS(ASTM D422, D1140 AND AASHTO T88)
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Sieve No. Opening (mm)
Opening (in) Notes
3/4 in 19 0.75 Gravel
#4 4.75 0.187
Course Sand(#4 to #10)
#6 3.35 0.132
#8 2.36 0.0937
#10 2.00 0.0787
#16 1.18 0.0469
Medium Sand(#10 to #40)
#20 0.85 0.0331
#30 0.60 0.0234
#40 0.425 0.0165
#50 0.300 0.0117
Fine Sand(#40 to #200)
#60 0.250 0.0098
#80 0.180 0.0070
#100 0.150 0.0059
#140 0.106 0.0041
#170 0.088 0.0035
#200 0.075 0.0029
#270 0.053 0.0021 Silt or Clay <#200
COMMONLYUSED
STANDARDSIEVESIZES
(ASTM E11-09e1)
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Definitions (from FHWA NHI-06-088)• Angular particles are those that have been
freshly broken up and are characterized by jagged projections, sharp ridges, and flat surfaces.
• Subangular particles are those that have been weathered to the extent that the sharper points and ridges have been worn off.
• Subrounded particles are those that have been weathered to a further degree than subangular particles.
• Rounded particles are those on which all projections have been removed, with few irregularities in shape remaining.
• Well rounded particles are rounded particles in which the few remaining irregularities have been removed. Mitchell (1976)
Fig. 2-4. FHWA NHI-06-088.
PARTICLE ANGULARITY (ROUNDNESS)
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HYDROMETER ANALYSIS(ASTM D442, D1140 & AASHTO T88)
Figure 2.5. Das FGE (2005).
Based on the principle of sedimentation of soil grains in water
Stokes Law:
Where:v = Velocitys = soil particle densityw = water density = water viscosityD = Diameter of soil particles
2
18D v ws
ASTM D152-Hhydrometer
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14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
Figure 2.6. Das FGE (2005).
Figure 5. ASTM D2487-11.
GRAIN SIZE DISTRIBUTION RESULTS
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Key Particle Sizes (D = Diameter)D60 = Diameter corresponding to 60% finer in
the grain size distribution.
D30 = Diameter corresponding to 30% finer in the grain size distribution.
D10 = Diameter corresponding to 10% finer in the grain size distribution. Also known as Effective Size.
GRAIN SIZE DISTRIBUTION TERMS
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Key Coefficients (C):Cu = Coefficient of Uniformity (ASTM D2487)
= D60/D10
Cc = Coefficient of Gradation= Coefficient of Curvature (ASTM D2487)= (D30)2/(D60xD10)
GRAIN SIZE DISTRIBUTION TERMS
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GRAIN SIZE DISTRIBUTION - EXAMPLE
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Figure 7.2. from FHWA NHI-01-031.
0102030405060708090
100
0.0001 0.001 0.01 0.1 1 10Grain Size (mm)
Perc
ent
Pass
ing
(by
weight
) Silica Sand
Piedmont Silt
Plastic Kaolin
CLAY SIZE SILT SIZE SAND SIZE GRAVEL
0.075 mm
Fine-Grained Soils Coarse-Grained Soils
Notice Axis Shift!
GRAIN SIZE DISTRIBUTION - EXAMPLE
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10 1 0.1 0.01Particle Diameter (mm)
0
10
20
30
40
50
60
70
80
90
100Pe
rcen
t (%
) Fin
er b
y W
eigh
t#4 #10 #30 #40 #60 #100 #200
#4 #10 #30 #40 #60 #100 #200
GRAVELSAND
Coarse FineSILT & CLAY
Medium
Multiple Samples
of “Same Soil” from
one site.
GRAIN SIZE DISTRIBUTION - EXAMPLE
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14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
(from Hajduk et al., 2004)
GRAIN SIZE DISTRIBUTION - EXAMPLE
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14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
Figure 2-5. FHWA NHI-06-088.
(a.k.a. ws) (a.k.a. wp) (a.k.a. wL)
Plasticity Index(PI) PI = LL - PL
Range of water content over which soil remains plastic.
SOIL PLASTICITY – ATTERBERG LIMITS
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SOIL PLASTICITY – ATTERBERG LIMITS
Figure 24. from FHWA IF-02-034.
LL and PL photographs courtesy Prof. Reddy, UIC.
Liquid Limit (LL or wL) Test
ASTM D4318-10 Standard TestMethods for Liquid Limit, PlasticLimit, and Plasticity Index of Soils.
Plastic Limit (PL or wP) Test
Liquid Limit Device
Plastic Limit Device
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ATTERBERG LIMITS – LIQUID LIMITASTM D4318-10 Standard Test Methods for Liquid Limit, Plastic Limit, andPlasticity Index of Soils.
Photographs courtesy of Engineering Properties of Soils Based on Laboratory Testing Manual, Prof. Krishna Reddy, UIC, 2002.
Fill LL Device ~2/3 high with wet soil.
Cut groove with tool.Assemble components & soil. Mix soil & water.
Lift LL Device with crank @ constant rate. Count number of blows to close
groove ½ inch.Mix soil with more water. Repeat.
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14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
Example of Liquid Limit Data Plot
Run 4 Tests2 > 25 blows2 < 25 blows.
Plot Number of Blows (N) onLog Scale.
LL is w @ N=25
(Round to 1%)
ATTERBERG LIMITS – LIQUID LIMIT
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14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
ASTM D4318-10 Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils.
Photographs courtesy of Engineering Properties of Soils Based on Laboratory Testing Manual, Prof. Krishna Reddy, UIC, 2002.
Run 4 Tests. Average water content for 4 tests = wP = PL
Assemble components & soil. Mix soil & water.
Roll wet soil to ellipsoidal mass with hands.
Roll on PL Device until 1/8 inch diameter roll is
achieved.
When soil crumbles when 1/8 inch diameter is
achieved, you are at PL. Take water content.
ATTERBERG LIMITS – PLASTIC LIMIT
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Divided into two broad categories:• Coarse Grained Soils
Gravels (G) and Sands (S)< 50% passing through #200 sieve(i.e. >50% retained on #200 sieve)
• Fine Grained SoilsSilts (M) and Clays (C)≥ 50% passing through #200 sieve
UNIFIED SOIL CLASSIFICATION SYSTEM(USCS)
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• Uses 2 or 4 letter Group Symbols and Group Names• Primary soil component first symbol• 4 letter symbols – either sands and gravels with
5% ≤% Fines ≤ 12% or CL-ML on Casagrande Chart
• Need to know the following:• Grain Size Distribution
• Percent Fines (i.e. particles finer than #200 sieve)• Percent Sand• Percent Gravel #4 and #200 sieves• Cc and Cu from grain size analysis using D10, D30, D60
• Atterberg Limit Results (LL, PI)
UNIFIED SOIL CLASSIFICATION SYSTEM(USCS)
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Example of 2 Group Symbol: SMPrimary Component (Sand = S)Secondary Description (M = Silty)
Secondary Descriptions (Coarse Grained)M = SiltyC = ClayeyP = Poorly Graded (same relative grain size)W = Well Graded (different grain sizes)
Primary ComponentsG = GravelS = SandM = SiltC = ClayO = Organic Secondary Descriptions (Fine Grained)
L = Low Plasticity (Lean for Clay)H = High Plasticity (Fat for Clay, Elastic for Silt)
UNIFIED SOIL CLASSIFICATION SYSTEM(USCS)
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Secondary Descriptions (Coarse Grained)M = Silty: > 12% fines, PI<4 or plots below “A” Line
C = Clayey: > 12% fines, PI>7 and plots on or above“A” line
P = Poorly Graded: < 5% fines, Cu < 6 and/or 1>Cc>3
W = Well Graded: < 5% fines, Cu ≥ 6 and 1 ≤ Cc ≤ 3
UNIFIED SOIL CLASSIFICATION SYSTEM(USCS)
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PARTICLE SIZE DISTRIBUTION CURVES
Three Types of Curves:
Poorly Graded (P)
Well Graded (W)
Gap Graded
Gap Graded
Figure 2-3. from FHWA NHI-06-088.
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14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
UNIFIED SOIL CLASSIFICATION SYSTEM(USCS)
Secondary Descriptions (Fine Grained)
L = Low Plasticity (Lean for Clay)(LL <50%)
H = High Plasticity (Fat for Clay, Elastic for Silt)(LL ≥ 50%) (e.g. high quality pottery clay)
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CASAGRANDE PLASTICITY CHART
Figure 4. (ASTM D2487-11).
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14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
I consider it essential that an experienced soils engineer should be able to judge the position of soils, from his territory, on a plasticity chart merely on the basis of his visual and manual examination of the soils. –Arthur Casagrande (1959)
CASAGRANDE PLASTICITY CHARTSIGNIFICANCE OF ATTERBERG LIMITS
Figure 2. (NAVFAC DM7.01).
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14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
USCS – COARSE GRAINED SOILS(>50% RETAINED ON #200 SIEVE)
Figure 3. ASTM D2487-11.
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USCS – FINE GRAINED SOILS(≥ 50% PASSING #200 SIEVE)
Figure 1. ASTM D2487-11.
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Sieve No. Dia. (mm) % Passing
½ in 12.7 100
#4 4.75 97
#10 2 94
#20 0.85 84
#40 0.425 57
#60 0.25 32
#140 0.106 15
#200 0.075 9
Table 1. Sample 1 Grain Size Results(ASTM D422).
Table 2. Atterberg Limits Results(ASTM D4318).
Sample LL PL
1 60 40
REQUIRED:Determine the USCS Soil Classification based on the provided soil index testing.
USCS CLASSIFICATION EXAMPLEUS44 EXPANSION, CARVER, MA
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14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
USCS CLASSIFICATION EXAMPLE
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USCS CLASSIFICATION EXAMPLE
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USCS CLASSIFICATION EXAMPLE
Fines classify as MH
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14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
Figure 3. ASTM D2487-11.
88% Sand
9% Fines
Cu = 5.63 Fines = MH 3% Gravel
ANSWER: SP-SM (Poorly Graded Sand with Silt)
USCS CLASSIFICATION EXAMPLE
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14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
ORIGIN (Holtz and Kovacs, 1981):This system was originally developed by Hogentogler and Terzaghi in 1929as the Public Roads Classification System. Afterwards, there are severalrevisions. The present AASHTO (1978) system is primarily based on theversion in 1945.
STANDARDS:AASHTO M145-91 (2003) Standard Specifications for Classification ofSoils and Soil-Aggregate Mixtures for Highway Construction Purposes.
ASTM D3282-09 Standard Practice for Classification of Soils and Soil-Aggregate Mixtures for Highway Construction Purposes.
AMERICAN ASSOCIATION OF STATE HIGHWAYAND TRANSPORTATION OFFICIALS (AASHTO)
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14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
A4 to A7A1 to A3
Using LL and PI separates siltymaterials from clayey materials
Using LL and PI separates siltymaterials from clayey materials
(only for A2 group)
Comprised of 8 Major Groups:A1 through A7 (with subgroups)A8 (Organics)Subgroups determined from Group Index (GI)
Required Testing:Sieve Analysis and Atterberg Limits
Granular Materials( 35% passes #200 Sieve)
Silt-Clay Materials(≥ 36% passes #200 Sieve)
General Notes:• A-1 materials are well graded, whereas A-3 soils are clean, poorly graded sands.• A4 & A5 are generally silts, A6 & A7 are generally clays.
AMERICAN ASSOCIATION OF STATE HIGHWAYAND TRANSPORTATION OFFICIALS (AASHTO)
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14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
STEPS:1. Determine Grain Size Distribution
(AASHTO T-11 & AASHTO T-27)2. Determine Liquid Limit (AASHTO T-89)3. Determine Plastic Limit (AASHTO T-90)4. Classify Soil using Table 2 ASTM 3282
(Left to Right Method, Process of Elimination)
AMERICAN ASSOCIATION OF STATE HIGHWAYAND TRANSPORTATION OFFICIALS (AASHTO)
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14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
Go from Left to Right, Process of EliminationTable 2 from ASTM D3282-09 Standard Practice for Classification of
Soils and Soil-Aggregate Mixtures for Highway Construction Purposes.
AMERICAN ASSOCIATION OF STATE HIGHWAYAND TRANSPORTATION OFFICIALS (AASHTO)
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14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
AMERICAN ASSOCIATION OF STATE HIGHWAYAND TRANSPORTATION OFFICIALS (AASHTO)
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14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
)10)(15(01.0)40(005.02.0)35( 200200 PIFLLFGI
)10PI)(15F(01.0GI 200
For Groups A-2-6 and A-2-7
The first term is determined by the LL
The second term is determined by the PI
In general, the rating for a pavement subgrade is inversely proportional to the group index, GI.
use the second term only
F200: % Passing #200 Sieve
Group Index (GI): Empirical Formula used to evaluate soils in a group (i.e. subgroup)
AMERICAN ASSOCIATION OF STATE HIGHWAYAND TRANSPORTATION OFFICIALS (AASHTO)
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14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
Group Index (GI): Empirical Formula used toevaluate soils in a group(i.e. subgroup)
AMERICAN ASSOCIATIONOF STATE HIGHWAY AND
TRANSPORTATIONOFFICIALS(AASHTO)
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14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
SOIL COMPOSITION: OVERVIEW
5 Main Groups1. Carbonates (calcite and dolomite to make cement)2. Oxides3. Hydrous Oxides4. Phospahates5. Silicates (>90% of all soil)
Differences in particle size and shape mainly due to differences in type and arrangements of elements in the crystalline structure (i.e. mineralogy).
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SOIL COMPOSITION: SILICATESSilica Tetrahedra
SiO4
+4 -8
Total Charge -4
Silica Frameworks & Composition of Granular SoilsTetrahedra form 3-D arrays so that ALL oxygen are shared (one Si per two Oxygen). Very resistant to weathering → large particles.
Quartz: 4(SiO2) = Si4O8K Feldspar: K Al Si3 O8
Side View Plan View
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Building Blocks of Clay Minerals
Si4O10
+16 -20 Total Charge -4.Still not neutral; combines with
octahedral sheets
Silica SheetSilica Sheet Draw it as this.
1. All basal oxygen are shared
SOIL COMPOSITION: CLAY MINERALS
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Building Blocks of Clay Minerals (continued)2. Hydrous Oxide Octahedral Sheets
G = Gibbsite
B = Brucite
Al4(OH)12
Mg6(OH)12
3. Which sheets (silica and hydrous oxide) are combined (via primary valence bonding) to form a layer and how these layers are “glued” together to form particles → different clay minerals.
SOIL COMPOSITION: CLAY MINERALS
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Common Clay Materials: Two SheetsKaolinite
G Repeating Unit
G
Held together by hydrogen bonding & van der Waals forces. Forms large blocks.
G
SOIL COMPOSITION: CLAY MINERALS
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Common Clay Materials: Two SheetsHalloysite
G
Water (4 H2O molecules) acts as weak glueG
Forms hollow tube structure.
SOIL COMPOSITION: CLAY MINERALS
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Common Clay Materials: Three SheetsMuscovite (Mica)
SOIL COMPOSITION: SILICATES
Isomorphous Substitution (IS): Some Si atoms replaced by Al atoms (~ 1 in 4)G
G
G
K KNegative charged particles due to IS. Balanced by K+
atoms (form very strong bond). Forms very large
plate like particles.
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14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
Common Clay Materials: Three SheetsIllite (Hydrous Mica)
Isomorphous Substitution (IS): Less Si atoms replaced by Al atoms → less K “glue” → smaller particles
G or B
G or B
G or B
KMost common clay mineral, especially in cold climates,
marine clays (e.g. BBC).
SOIL COMPOSITION: CLAY MINERALS
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Common Clay Materials: Three SheetsMontmorillonite (Smectite)
Isomorphous Substitution (IS): Some IS of Mg+2 for AL+3
in Gibbsite sheet (~1 in 6)G
G
G
Common mineral in arid regions from weathering of volcanic ash, alkaline igneous rocks, etc..
Sodium (Na+) Montmorillonite (Bentonite): Na+ cations do no “glue” layers together,
resulting in thin particles
Na+1, Ca+2, etc.
SOIL COMPOSITION: CLAY MINERALS
Revised 01/2013
14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL
Common Clay Materials: Three Sheet SizesSOIL COMPOSITION: CLAY MINERALS
Kaolinite (t ≈ 1000 Å (140 layers), l ≈10,000 Å, SSA ≈ 10 m2/g)Kaolinite (t ≈ 1000 Å (140 layers), l ≈10,000 Å, SSA ≈ 10 m2/g)
Illite (t ≈ 100 Å (10 layers), l ≈3,000 Å, SSA ≈ 80 m2/g)
Illite (t = 10 Å (1 layers), l ≈ 1,000 Å, SSA ≈ 800 m2/g)
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