14.531 advanced soil mechanics p n so, this...

Revised 01/2014

14.531 ADVANCED SOIL MECHANICSPART II - THE NATURE OF SOIL

SO, THIS PICTURE KEEPS POPPINGINTO MY TIMELINE…

A Philosophy Professor stood before his class…

Revised 01/2014


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?

Revised 01/2014


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

Revised 01/2014


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

Revised 01/2014


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


3 PHASE DIAGRAM

Revised 01/2014


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

Revised 01/2014


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)

Revised 01/2014



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

Revised 01/2014



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

Revised 01/2014


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

Revised 01/2014


Table 3.1. Das FGE (2005).

KEY RELATIONSHIPS:INDEX PROPERTIES SUMMARY & APPLICATIONS

Revised 01/2014


Where:

S = Degree of Saturatione = Void Ratiow = Moisture ContentGs = Specific Gravity of Solids


Se wGs

KEY EQUATION OFSOIL COMPOSITION

Revised 01/2014


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 10 134

Revised 01/2014


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).

Revised 01/2014


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

Revised 01/2014


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)

Revised 01/2014


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)

Revised 01/2014


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)

Revised 01/2014


HYDROMETER ANALYSIS(ASTM D442, D1140 & AASHTO T88)


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

Revised 01/2014



Figure 5. ASTM D2487-11.

GRAIN SIZE DISTRIBUTION RESULTS

Revised 01/2014


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

Revised 01/2014


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

Revised 01/2014


GRAIN SIZE DISTRIBUTION - EXAMPLE

Revised 01/2014


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!


Revised 01/2014


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.


Revised 01/2014


(from Hajduk et al., 2004)


Revised 01/2014


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

Revised 01/2014


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

Revised 01/2014


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.

Revised 01/2014


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

Revised 01/2014


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

Revised 01/2014


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)

Revised 01/2014


• 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)


Revised 01/2014


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)


Revised 01/2014


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


Revised 01/2014


PARTICLE SIZE DISTRIBUTION CURVES

Three Types of Curves:

Poorly Graded (P)

Well Graded (W)

Gap Graded

Gap Graded


Revised 01/2014



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)

Revised 01/2014


CASAGRANDE PLASTICITY CHART

Figure 4. (ASTM D2487-11).

Revised 01/2014


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).

Revised 01/2014


USCS – COARSE GRAINED SOILS(>50% RETAINED ON #200 SIEVE)


Revised 01/2014


USCS – FINE GRAINED SOILS(≥ 50% PASSING #200 SIEVE)


Revised 01/2014


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

Revised 01/2014


USCS CLASSIFICATION EXAMPLE

Revised 01/2014



Fines classify as MH

Revised 01/2014



88% Sand

9% Fines

Cu = 5.63 Fines = MH 3% Gravel

ANSWER: SP-SM (Poorly Graded Sand with Silt)


Revised 01/2014


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)

Revised 01/2014


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.


Revised 01/2014


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)


Revised 01/2014


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.


Revised 01/2014



Revised 01/2014


)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)


Revised 01/2014


Group Index (GI): Empirical Formula used toevaluate soils in a group(i.e. subgroup)

AMERICAN ASSOCIATIONOF STATE HIGHWAY AND

TRANSPORTATIONOFFICIALS(AASHTO)

Revised 01/2014


Granular Soils• Large grain sizes• Small Specific

Surface Area (SSA)• Larger voids• Higher k

(permeability)• Free draining

SOIL TYPES(TWO GENERAL CATEGORIES)

Cohesive Soils• Small grain sizes• Large Specific

Surface Area (SSA)• Surface properties

dominate• Drainage is f(t)

SSA = Total Surface Area per Volume

Revised 01/2014


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).

Revised 01/2014


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

Revised 01/2014


Building Blocks of Clay Minerals

Si4O10+16 -20

Total Charge -4.Still not neutral; combines with

octahedral sheets

Silica SheetSilica SheetDraw it as this.

1. All basal oxygen are shared

SOIL COMPOSITION: CLAY MINERALS

Revised 01/2014


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.


Revised 01/2014


Common Clay Materials: Two SheetsKaolinite

G Repeating Unit

G • Held together by hydrogen bonding & van der Waals forces.

• Forms large hexagonal platy shaped particles

G


~7Å

1Å = 10-10 meter = 0.1nm

Revised 01/2014


Common Clay Materials: Two SheetsHalloysite

G

Water (4 H2O molecules) acts

as weak glueG

Forms hollow tube structure.


~10Å

• Same basic structure as kaolinite, but 4 H2O molecules trapped between layers during formation (hydrated form).

• Due to slight mismatch in crystal structure of G & S sheets, forms hollow tubes.

• Tubular particles + trapped water → high w and low d(even after compaction).

Revised 01/2014


Common Clay Materials: Three SheetsMuscovite (Mica)


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.

Revised 01/2014


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

K

Most common clay mineral, especially in cold climates, marine

clays (e.g. BBC).


Revised 01/2014


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.


Revised 01/2014


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)

Montmorillonite (t = 10 Å (1 layers), l ≈ 1,000 Å, SSA ≈ 800 m2/g)

Extremely high SSA. Used as seals (expands) in slurry walls. Cat litter.

14.531 advanced soil mechanics p n so, this...

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