66

HOW TO DESIGN?

DISTRIBUTION OF EXPANSIVE SOILS

WIDE VARIETY OF CLIMATE

SAME SOIL -- DIFFERENT CLIMATE

RESIDENCE COMPLICATIONS

DESIGN NEEDS ENVELOPES

EDGE LIFT

EDGE DRYING

DESIGN AIDS

• SOIL MOVEMENT

• SOIL MOVEMENT TABLES

• SLAB DEFLECTION AND STRESSES

• SOIL VOLUME CHANGE

• SOIL MOISTURE VARIATION DISTANCE

• VERTICAL BARRIERS

SOIL SUCTION

EXAMPLE: VOLFLOEXAMPLE: VOLFLO--22GIVEN VALUES:

• UWET = 2.50 pF

• UDRY = 4.56 pF

• Zm = 28.08 ft

• UEQUIL. = 3.31 pF

• UO = 1.03 pF

• n = 1 cycle/year

SOIL MOVEMENT

SOIL MOVEMENT

SOIL MOVEMENT

SOIL MOVEMENT

SOIL MOVEMENT

SOIL MOVEMENT TABLES

Design Differential Soil Movement, ym,Guide Number for Slab Design

ym Guide Numbers

Controlling Surface Suction, pF

MeasuredSuction pF at

Depth, zm,m 2.5 2.7 3.0 3.5 4.0 4.2 4.52.7 +3.2 0 -4.1 -13.6 -25.7 -31.3 -40.0

3.0 +9.6 +5.1 0 -7.5 -18.2 -23.1 -31.3

3.3 +17.7 +12.1 +5.1 -2.6 -11.5 -15.8 -23.1

3.6 +27.1 +20.7 +12.1 +1.6 -5.7 -9.4 -15.8

3.9 +38.1 +30.8 +20.7 +7.3 -1.3 -4.1 -9.4

4.2 +50.4 +42.1 +30.8 +14.8 +3.2 0 -4.1

4.5 +63.6 +54.7 +42.1 +23.9 +9.6 +5.1 0

Note: The positive sign indicates heave and the negative sign indicates shrinkage.


Design Differential Soil Movement, ym, Guide Numberfor Slab Design: Lawn Irrigation

ym Guide Numbers

Controlling Surface SuctionDue to Lawn Watering

pF – unitsWith 4 ft. Deep Moisture Barrier

pF -- units


Depth, zm,m

2.5 2.7 3.0 3.5 2.5 2.7 3.0 3.52.7 3.2 0 0 0 0.1 0 0 0

3.0 9.6 5.1 0 0 0.1 0.1 0 0

3.3 17.7 12.1 5.1 0 0.1 0.1 0.1 0

3.6 27.1 20.7 12.1 1.6 1.3 0.5 0.1 0.1

3.9 38.1 30.8 20.7 7.3 3.8 1.9 0.5 0.1

4.2 50.4 42.1 30.8 14.8 7.7 4.9 1.9 0.1

4.5 63.6 54.7 42.1 23.9 12.4 9.1 4.9 0.8


Design Differential Soil Movement, ym, Guide Numberfor Slab Design: Flower Bed Case(4 ft Deep Flower Bed Moisture)

ym Guide Numbers

Controlling Surface Suction Due toFlower Bed Watering

pF – unitsWith 4 ft. Deep Moisture Barrier

pF -- units


Depth, zm,m

2.5 3.0 3.5 2.5 2.7 3.0 3.52.7 3.2 0 0 0 0 0 0

3.0 13.1 0 0 0 0 0 0

3.3 27.3 7.0 0 3.7 1.0 0 0

3.6 48.7 14.2 1.6 11.6 6.2 1.1 0

3.9 69.5 35.1 10.2 22.5 15.2 6.4 0

4.2 90.3 56.0 21.5 35.1 26.6 15.3 2.4

4.5 111.0 76.7 42.3 49.0 39.7 26.6 9.1


Design Differential Soil Movement, ym, Guide Numberfor Slab Design: Tree Drying Case

(Without Moisture Barrier)

ym Guide Numbers

Measured Equilibrium Suction at Depth, zm

pF -- units

Depth ofTree RootZone, ft

2.7 3.0 3.3 3.6 3.9 4.2 4.54 -79.1 -60.1 -43.2 -28.4 -15.6 -0.1 0.0

10 -169.6 -146.3 -124.9 -82.8 -42.6♦ -9.7♠ 0.0

15 -244.7 -213.6 -182.5 -108.1♥ -42.6♦ -9.7♠ 0.0

20 -333.4 -292.9 -252.5 -108.1♥ -42.6♦ -9.7♠ 0.0

♥Movement active zone, zA = 11.5 ft.♦Movement active zone, zA = 7.5 ft.♠Movement active zone, zA = 3.5 ft.


Design Differential Soil Movement, ym, Guide Numberfor Slab Design: Tree Drying Case

(With Moisture Barrier)

ym Guide Numbers

Measured Equilibrium Suction at Depth, zm

(With 4 ft Deep Moisture Barrier)pF -- units

Depth ofTree RootZone, ft

2.7 3.0 3.3 3.6 3.9 4.2 4.54 -36.5 -25.2 -15.8 -8.1 -2.6 0.0 0.0

10 -116.3 -102.4 -88.4 -53.1 -21.5♦ 0.0 0.0

15 -193.5 -170.5 -147.5 -78.5♥ -21.5♦ 0.0 0.0

20 -278.2 -246.1 -214.2 -78.5♥ -21.5♦ 0.0 0.0

♥Movement active zone, zA = 11.5 ft.♦Movement active zone, zA = 7.5 ft.

SLAB DEFLECTIONSAND STRESSES

EXAMPLE NO. 1P.T.I. DESIGN MANUAL

FLAT SLABFLAT SLABRIBBED SLABRIBBED SLAB

SOIL VOLUME CHANGECHARTS

NATURAL RESOURCESCONSERVATION SERVICE

U.S.D.A.DATA BASE

(130,000 SAMPLES)(130,000 SAMPLES)

EXPANSIVE SOILS ZONES(A. P. COVAR)

0 10 20 30 40 50 60 70 800

10

20

30

40

50

60

70

80

B-L

ine

Upper Lim

it of C

hart (P

I=LL

)

Any m

inera

l plo

tting i

n this

zone

sho

uld be in

cluded in

ZoneI

PI = 0.9

0(LL-8

)

U-L

ine

Montmorill

onite

I

PI = 0.85(LL-1

1)

Mixed M

inerals

PI = 0.81(LL-1

4)

Illites

PI = 0.73(LL-20)

A-Line

Kaolinite

s

PI = 0.68(LL-25)

Halloysites

Chlorit

es

LIQUID LIMIT, %

PLA

ST

ICIT

Y IN

DE

X, %

II

III

IV

V

VI

VIII

VII

EXPANSIVE SOIL VOLUME CHANGE GUIDE NUMBER(A. P. COVAR)

ZONE 1ZONE 1


ZONE 2ZONE 2


ZONE 3ZONE 3


ZONE 4ZONE 4


ZONE 5ZONE 5


ZONE 6ZONE 6


ZONE 7ZONE 7


ZONE 8ZONE 8

VOLUME CHANGECOEFFICIENT, γγhh

==PERCENT FINE CLAY

××VOLUME CHANGE

GUIDE NUMBER

EDGE MOISTUREVARIATION DISTANCE,

eemm, ft

EDGE MOISTURE VARIATION DISTANCE

α(cm2/sec), Unsaturated Diffusivity Coefficient

10

2

e m(f

t), E

dge

Moi

stur

e V

aria

tion

Dis

tanc

e100

90

80

70

60

50

40

30

20

10

0

-5

-10

-15

-20

-25

-30

S, S

lope

of p

F--

vs--

Wat

er C

onte

nt C

uve

Per

cent

Pas

sing

#20

0 S

ieve

(%

)

1020

30 4050

6070

PLAS

TICI

TY IN

DEX (PI,

%)

2030

4050

6070

8090

100

LIQUID

LI

MIT (L

L, %)

0.0E+0 1.0E-3 2.0E-3 3.0E-3 4.0E-3 5.0E-3 6.0E-3 7.0E-3 8.0E-3

3

4

5

6

7

8

9

0.25 0.20 0.15 0.10 0.05 0.00

VOLUME CHANGE COEFFIC

IENT

(SUCTION CO

MPRESSIO

N INDEX,γ

h )

CENTER LIFTEDGE LIFT

EFFECT OF VERTICALMOISTURE BARRIER

MOISTURE BARRIER(T = 1.5 ft)(T = 1.5 ft)

Depth of Perimeter Beam Below Ground Level or Depth of Vertical Moisture Barrier Below Ground Level, D', FT

1

2

3

4

5

6

7

8

9

10

11

12

13

1 2 3 4 5 6 7 8 9 10 11

Design Value of the Edge Moisture Variation Distance, e'm, ft.

Ed

ge

Mo

istu

re V

aria

tio

n D

ista

nce

fo

r M

ois

ture

Flo

w, e

m, f

t.

T = 1.5 FT

6'--5.5' 5' 4.5' 4' 3.5' 3' 2.5' 2' 1.5' 1'

D' T

em'



1

2

3

4

5

6

7

8

9

10

11

12

13

1 2 3 4 5 6 7 8 9 10 11


Ed

ge

Mo

istu

re V

aria

tio

n D

ista

nce

fo

r M

ois

ture

Flo

w, e

m, f

t.

T = 2 FT

6' 5.5' 5' 4.5' 4' 3.5' 3' 2.5' 2' 1.5' 1'

D' T

em'



1

2

3

4

5

6

7

8

9

10

11

12

13

1 2 3 4 5 6 7 8 9 10 11


Ed

ge

Mo

istu

re V

aria

tio

n D

ista

nce

fo

r M

ois

ture

Flo

w, e

m, f

t.

T = 2.5 FT

6' 5.5' 5' 4.5' 4' 3.5' 3' 2.5' 2' 1.5' 1'

D' T

em'

DESIGN AIDSDESIGN AIDSFORFOR

SLABS ONSLABS ONEXPANSIVE SOILSEXPANSIVE SOILS

66

Documents

tree drying case

tree root zone

vertical moisture barrier

movement active zone

moisture barrier

expansive soils

soil movement

moisture flow