2 soil-classification ( Highway Engineering Dr. Sherif El-Badawy )

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Material Properties Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

Material Types

• Unbound (soil)

• Natural (i.e., subgrade)

• Select (i.e., subbase, base)

• Asphalt concrete

• Portland cement concrete

• Stabilized materials

• Cement stabilized

• Bituminous stabilized

• Bedrock

• Recycled

Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

Material Properties Needed for Design

• Pavement response model material inputs • Modulus (stiffness)

• Poisson’s ratio

• Materials-related pavement distress criteria • Permanent deformation resistance

• Fatigue resistance

• Strength

• Other material properties • Density

• Permeability

• Thermal expansion coefficient


Material Models

(Yoder and Witczak, 1974)

2


Material Models

• Linear elasticity

• Asphalt

• Stabilized layers

• Unbound layers

• Linear viscoelasticity

• Asphalt

• Nonlinear (all materials, to some extent)

• Nonlinear elasticity

• Plasticity

• Nonlinear viscoelasticity

• Viscoplasticity


Soil Classification

Systems


Soil Classification

The separation of soil into classes or groups each having similar characteristics and potentially similar behaviour

Few simple (routine) tests are used to classify soils.

Gradation (Sieve Analysis)

Atterberg Limits (LL & PL)


Soil Classification Systems

• MIT

• AASHTO

• USCS

• FAA

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MIT Classification Material Size (mm)

Boulder > 60

Gravel

Fine 2 – 6

Medium 6 – 20

Coarse 20 – 60

Sand

Fine 0.06 – 0.2

Medium 0.2 – 0.6

Coarse 0.6 – 2

Silt

Fine 0.002 – 0.006

Medium 0.006 – 0.02

Coarse 0.02 – 0.06

Clay < 0.002


AASHTO Classification

• AASHTO: American Association of State

Highways and Transportation Officials

• Used mainly for subgrade rating for

highway purposes.

• Requires:

• Gradation

• LL

• PI

AASHTO Classification

**For A-7-5 soil PI ≤ LL-30, For A-7-6 soil PI > LL-30

#10

#40

#200

Granular Material (%P#200 ≤ 35%) Fine Grained Material

(%P#200 > 35%)

Characteristics of

Material P#40


Notes

• NP = Non Plastic (No Clay)

• The First Group to Fit the Date from the Left is the Correct

AASHTO Classification.

• The Placement of A-3 before A-2 is necessary for the left to

right process and does not indicate superiority of A-3 over

A-2

**For A-7-5 soil PI ≤ LL-30

**For A-7-6 soil PI > LL-30

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Group Index (GI)

• GI is used to evaluate soils within one group.

• GI = 0.2 a + 0.005 a.c + 0.01 b.d (0 to 20)

a = %P#200 – 35 (0 to 40)

b = %P#200 – 15 (0 to 40)

c = LL – 40 (0 to 20)

d = PI – 10 (0 to 20)

• GI to the nearest whole number (integer)

• High GI low quality material

• EX: A-7-6(5), A-7-6(18)


USCS Classification

• USCS: Unified Soil Classification

System

• Used mainly for geotechnical purposes

• Requires: • Gradation

• LL

• PI


USCS Classification

Soil Symbol Property Symbol

Gravel G Well Graded W

Sand S Poor Graded P

Silt M High LL (High Plasticity) H

Clay C Low LL (Low Plasticity) L

Peat Pt Clay C

Organic

soil

O Silt M

EX: SC Clayey Sand EX: Dual Symbol: SP-SM

GW Well Graded Gravel poorly graded sand

CL Clay with low plasticity with silt


Computing CU and CC

Coefficient of Uniformity

Coefficient of Curvature

High Values Indicate Well-

Graded Soil

Values Between 1-3 Indicate

Well-Graded Soil

10

60

D

DCU

6010

230

DD

DCC

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A-Line Chart

Separates Clays and Silts

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90 100

LIQUID LIMIT

PL

AS

TIC

ITY

IN

DE

X CH

CL

ML

MH

CL-ML

ML &

OL

OH &

MH


USCS Classification


USCS Classification (Coarse-Grained)

Coarse-

Grained

Soils

%P#200

≤50%

% P #4 < 50%

(Gravel, G)

Less than

5% Fines

Cu>4, Cc = (1-3) G

W

Not satisfying GW GP

More than

12% Fines

A.L. Below A-Line or PI<4 GM

PI>7& A.L. Above A-Line GC

% P #4 > 50%

(Sand, S)

Less than

5% Fines

Cu>6, Cc = (1-3) SW

Not satisfying SW SP

More than

12% Fines

A.L. Below A-Line or PI<4 SM

PI>7& Above A-Line SC


USCS Classification (Fine-Grained)

Fine-

Grained

Soils

%P#200>

50%

LL<50%

ML

CL

OL

LL>50%

MH

CH

OH

Highly Organic Soils Pt

0

10

20

30

40

50

60

0 20 40 60 80 100

LIQUID LIMIT

PL

AS

TIC

ITY

IN

DE

X

CH

CL

ML

MH

CL-ML

OH & MH

ML

&

OL

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USCS Dual Symbols

For the following conditions a dual symbol

should be used:

a) 5% < %P#200 < 12%

The first symbol is indicative of the gradation (W or

P), the second symbol is indicative of the fines.

EX: SP-SM poorly graded sand with silt

b) Fine grained soils within the shaded zone in the A-

line chart (PI between 4 and 7, LL between 12 and

25).

EX: CL-CM, Silty clay with Low LL


Comparison between the AASHTO and

Unified Systems

• Both systems are based on the texture and plasticity of the soil.

• Both systems divide the soils into two major categories: Coarse grained and Fine grained based on %P#200 SI sieve.

• AASHTO: • %P#200 < 35% Coarse grained

• %P#200 > 35% Fine grained

• Unified: • %P#200 < 50% Coarse grained

• %P#200 > 50% Fine grained


Comparison between the AASHTO and

Unified Systems (Cont’d)

• AASHTO: #10 sieve separates gravels and

sand

• Unified: #4 sieve separates gravels and

sand

• AASHTO : There is no organic soil

• Unified : There is organic soil

• AASHTO: gravely and sandy soils are not

clearly separated

• Unified: gravely and sandy soils are clearly

separated

Mansoura University - Faculty of Engineering – Public Works Engineering Dept. (NCHRP 1-37A. 1999)

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Mansoura University - Faculty of Engineering – Public Works Engineering Dept. (Das, 1990) Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

FAA Classification

• FAA: Federal Aviation Administration

• Used mainly for soil classification for airport

construction.

• Requires: • Gradation

• LL

• PI

FAA Classification (Yoder & Witczak 1975)

Soil

Group

% R#10 %P#10,

R#60

%P#60,

R#270

%P#270 LL PI

E-1 0-45 40+ 60- 15- 25- 6-

E-2 0-45 15+ 85- 25- 25- 6-

E-3 0-45 - - 25- 25- 6-

E-4 0-45 - - 35- 35- 10-

E-5 0-55 - - 45- 40- 15-

E-6 0-55 - - 45+ 40- 10-

E-7 0-55 - - 45+ 50- 10-30

E-8 0-55 - - 45+ 60- 15-40

E-9 0-55 - - 45+ 40+ 30-

E-10 0-55 - - 45+ 70- 20-50

E-11 0-55 - - 45+ 80- 30+

E-12 0-55 - - 45+ 80+ -

E-13 Muck and Peat – Field Examination Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

FAA Classification Chart for Fine-Grained

Soils

80

70

60

50

40

30

20

10

0 10 20 30 40 50 10 60 70

E-12

E-9 E-10

E-8

E-7

E-6

Plasticity Index

liq

uid

Lim

it

E-11

100

90

(Yoder & Witczak 1975)

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It is Hard to be

an engineer!