RATIO OF VERTICAL TO

HORIZONTAL PERMEABILITIES OF

COMPACTED SOILS

ABSTRACT

The variation of permeability ratio

(rk=kh/kyJ of compacted soils can be

between 1 to 40 times. This ratio is very

important for seepage and stability analysis

of earth embankment.

The samples were selected from

Nong Pia Lai Dam, Rayong Province and

Khlong Phrung Dam, Chantaburi Province.

Both field compacted samples and repre­

sentative samples from the borrow area were

obtained for laboratory tests. the constant

head permeability test was adapted for

determination of vertical and horizontal

Warakorn Mairaing'

Sommai Lapkrengkrai 2

permeability. While others physical proper­

ties such as gradation, plasticity, void ratio

etc. were also determined to obtain the

correlation to permeabilites.

The results show that for Nong Pia

Lai Dam the horizontal permeabilities are -6 -4

ranging between 1 x 1 to 1.5 x 10 cm/s. and -7

the vertical permeabilities are between 5 x 10

-.to 6xlO cm/s with ratio ofkh/k, is 2.1­

7.0. The impervious core materials from

Khlong Phrung Dam show the variation of -6

horizontal and vertical between 4.5 x 10 to

1 Assistant Professor, Department of Civil Engineering, Faculty of Engineering, Kasetsart

University

2 Graduate Student, Department of Civil Engineering, Faculty of Engineering, Kasetsart

University

-4 -6-4 5 X 10 cm/s and 1.8 x 10 to 6 x 10 cm/s.

respectively with ratio of k h / k v is 2.2-7.5.

The factors affecting permeabilities

are hydraulic gradient (i), soil plasticity

(LL.) and the number oftest repetition (N).

Both coares grained and fine grained soil

show the decreasing of permeability when

the plasticity were increased but more

pronounce on coarse grained soil. The

permeability decreasing to a constant value

at i~ 300 and need about 12 cYies to stabilize

the whole permeability. This phenomena is

affected by migration of fine particle to

downstream and accumulated at exit end of

the samples. The fine grained soil show more

particle migration.

INTRODUCTION

Permeability or hydraulic con­

ductivity is an important engineering prop­

erty of soil defined as seepage velocity of

water through soil under unit hydraulic

gradient. It can vary widely even in com­

pacted soil such as on earth dam, dike. canal

lining or road embankment. The

permeabilities of soil have direct effects to

seepage loss, internal erosion, piping poten­

tial, filter design, stability of slope, rate of

consolidation etc. of many earth structures.

For completed soil, the arrangement to soil

particles after compaction tends to create the

anisotropic properties of the permeability.

The ratio ofhorizontal to vertical permeabilites

of earth dams were reported very from 4 to

25 times depending on soil type and

L'li~Vi 19 U'il:<i1l:1 2536

compaction method. This paper reports the

results of permeability tests of compacted

soils both from field and laboratory

compaction. The horizontal to vertical

permeabilities ratio are studies related to soil

type, applied hydraulic gradient, pressure

cycle and particle migration.

ANISOTROPY OF SOIL PER­MEABILITY

The fine grained soils usually con­

sist of large amount of platy particles. When

they are subjected to compactive energy, the

soil structure tends to be more dispersed for

the compaction on the wet side as compared

to dry side of optimum water contents

(Lambe 1962). The larger the compactive

energy cause more parallel particle arrange­

ment than the lower one as show on Figure

1. The particle shapes also has an intluence

the tlow characteristics as also on Figure 2.

The coarse grained soils with blockly, pris­

matic or granular shape normally do not

show the difference of horizontal to vertical

permeability.

The sedimentation characteristic of

the natural deposit of soil also show more

parallel than random particle arrangement.

This the development of anisotropic perme­

ability as a result of soil structure anisotropic

is quite obvious. In the field, the gross

anisotropic may exist in layered soil, sand

seams and the horizontal compacted layer.

The ratio (fk) between the horizontal and

vertical permeability of more than one are

usually observed as show on Table 1.

EFFECTS OF PERMEABILITY RATIO TO EARTHDAM.

In embankment of earth dam, the

anisotropic permeability of the dam body

can produce three major effects to the dam

namely;

(a) seepage quantity,

(b) drainage design, and

(c) slope stability

Cedergren (1967) studied the ef­

fect of embankment anisotropic by various

degrees of stratification as shown on Figure

3. The higher the permeability ratio the morc

seepage quantity is created and wider the

horizontal drain is required. For zoned dam

on Figure 4 shows the rising of pheartic lines

on downstream shell therefore the larger

drainage capacity is ueeded.

The stability of dam slopes are also

depended on the permeability ratio such as

the example of the dam shown on Figure 5

and 6. The homogeneous dams with toe

drain and horizontal drain filter show the

decreasing of the factor of safety when the

permeability ratio increasing from 1 to J 9.

This is one reason of using chimney drainlo

intercept the downstream seepage on high

earthdam for more effective drainage.

TESTING PROCEDURE The soil samples from 2 dam sites

from the eastern Thailand were taken as

followings.

Khong Pluang Dam, Chantaburi

Province, 55 m. high zoned dam, total filled

volume 8.0 millon cU.m.

KP1 - Field compactd core ma­

terial.

KP2 - Field compacted random

material.

KP3 - Laboratory compacted core

material from borrow area.

Nong Pia Lai Dam. Rayong

Province, 25 m. high homogeneous dam,

total filled volume 4.5 million cU.m.

NPL1 - Field compacted embank­

ment material, lower part.

NPL2 - Field compacted em­

bankment material, uppcr part.

NPL3 - Laboratory compacted

embankment material, from borrow area.

The laboratory compactions were

done on 6" mold using Standard Proctor

Compaction Method. The method of sample

preparation to obtain vertical and horizontal

permeability tested samples are as shown on

Figure 7. The permeability test equipments

were customized design for six samples and

the pressure is controlled by compressed air

as shown on Figure 8. The deairing and

saturation periods of 24 and 48 hrs. are using

before the tests. The pressurized head of 10,

20, 30, ... 80 meters were used for both

loading and unloading cycles or until blow

out effect occurred. The soil physical

properties such as the gradation, Atterberg's

limit, G, e. % density and water contend were

performed prior to the permeability tests and

the gradation test, density and water content

were rechecked again after the permeability

test. Figure 9 shows the schematic diagram

of the testing procedure.

INITIAL PHYSICAL PROPER­

TIES The physical properties of mate­

rials from both dams are summarized on

Table 1. The KP1, KP2 and KP3 are quite

different while the samples from Nang PIa

Lai dam are relatively similar.

FACTORS AFFECT

PERMEABILITIES The test indicated that they need 8

to 12 test repetitions to stabilize the

permeabilities to a constant level. Table 2

shows the range of permeabilities and per­

meability ratio.

The factors affecting both hori­

zontal and vertical permeabilities are as

follows.

a) soil plasticity

The plot of liquid limits versus

permeabilities on Figure 10 indicates clearly

that soils with higher LL. show lower

permeability since the diffused double layer

around the clay particles become thicker and

then channels offree water between particles

are decreased. The permeability ratio (rk) is

not clearly affected by the plasticity.

,.. ., 0 ""

L~UJ'VI 1 9 1J"'~"l11J 2 5 3 6

b) Applied hydraulic gradient

The horizontal permeability seems

to decrease as show on Figure 11 causing the

permeability ratio (rk) to decrease from 10

to 2.5 for samples from KP1 group, as shown

in Figure 12. However, this phenomenon is

not clealy found for the relatively coarser

grained soils such as the NPL1, NPL2, and

NPL3 groups.

c) Number of test repetition

Generally during the first eight to

twelve test cycles. the permeabilities on both

directions are quite fluctuated but gradually

stable after twelve cycles. Figure 13 shows

the typical variation of permeabilities versus

cycles. But the permeability ratio seems to

be constant regardless of number of test

cycles as shown on Figure 14.

PARTICLES MIGRATION When water flows through a soil

mass. the hydraulic head is loss by drag force

between water and soil surface. If the seep­

age velocity or hydraulic gradient is high

enough, the soil particle can migrate with the

water. This phenomenon will go on until the

moving particles can form a filter cake at the

exit end adjacent to actual filter layer.

However if the gradient is too high or the

filter can not protect the particle migration.

the blowout or erosion will occur. During

the permeability test, there is quite clear

evident of particle migration observed.

The samples were divided into 4

parts, top, middle bottom and bottom parts.

Ul'l:l1t1~ - n'ln!j1IUI

The samples from each part were taken to

check the final gradations. The soils from

KP1, KP2 and KP3 show the change of

gradation from coarse to finc particles from

the top to the bottOm as show on typical

curves in Figure 15.

The samples from Nang Pia Lai

Dam (NP1, TO 3) did not show the distinctive

differences of gradation along the sample

length. When the percentages of particle

passing # 200 sieve are plotted along the

sample length on Figure 16, the similar

rcsults are obtained. The repetition of pres­

sure will generally accelerate the particle

migration.

CONCLUSION

The study of thc pcrmeability

properties of compacted soils from two dams

in horizontal and vertical directions yields

the following conclusions.

1. Anisotropic penneability of

compacted soils has several effects to the

earthdam and othcr water retention structures

such as rising top flowline, lowering slope

stability and increasing seepage flow.

2. The horizontal permeabilities

ratios (rk = k h/ k ) of relatively fine grained v

soils (KP1 , KP2 and KP3) are ranging from

2.1 to 7.0 with an average value of 4.9 while

rk of coarse materials (NP1, NP2 and NP3)

are between 2.2 to 7.5 with an average of 4.5.

3. The applied hydraulic gradient

and number of repetition stimulate thc par­

ticle migration though soil mass. When the

migrations slowing down the relatively con­

stant penneabilities arc attened.

4. The permeabilities are de­

creased as the liquid limits are increased.

This correlation shows a good trend for the

group of soils from the same geological

origin.

5. The particle migration during

the tests is shown by changing of gradation

of soil from the top to the bOllom of the

sample. The migrated soil particles will fonn

a filter cake at the exit end if the actual filter

can effectively protect the further migration.

REFERENCE

1. Lambe, T. W., 'Soil Stabilization",

Chapter 4 of Foundation Engineering,

G.A. Leonards (editor), Mc Graw­

Hill, New York (1962)

2. Cedergren, H.R., "Seepage, Drainage,

and Flownets," John Wiley and Sons,

Inc, (1967)

3. Johnson, A.I., 'Symposium on Per­

meability of Soil,' ASTM STP 163,

American Society for Testing Materi ­

als' Philadelphia (1954)

4. Chan, H.T. and Kenny, T.e., 'Pore

Pressure and Suction in Soils,' J. Ca­

nadian Geotechnical, 10(3): 473-478.

5. Barden, L. and Sides, G.R.. 'Engineering

Behaviors and Structure Compacted

Clay,' J. Soil Mech. Found Div., ASCE

(SM4): 1171-1200

6. Olson, R.E. and Daniel, DE, 'Meas­

urement of Hydraulic Conductivity of

,.. -, . "" L~UJ'I'I 19 u~::'l1u 2536

Fine Grained Soils"" In Zimmic, T.F.,

and Riggs, C.O.R. (eds), Permeability

and Ground Water Contaminant

TranspOrl, ASTM STP 746, American

Society for Testing Materials, Phila­

delphia (1981 )

7. Besmister, D.M., 'PermeabilityofSoils",

ASTM SPP (63), American Society for

Testing Materials, Philadelphia (1954)

B. Aitchison, GD. and Wood., 'Some

Interaction ofCompaction, Permeability

and Post-construction Deflocculation

an Affecting the Proability of Piping

Failure in Small Earth Dam: In proc.

6th Int. ConI., Soil Mech. Found.,

Canada (1965)

Table 1. Initial Physical Properties

PHYSICAL PROPERTIES

-OFSC-SOIL CLASS.

lUILONC PLUANG DAK lfONe PLA UI ."" ... .., .., NPLI ItPLl NPL)

CH.HH 'C CL ( , -ARkTEkBERG'S LIMITS

- LL 48-56 32-36 '5-JI!l (­r- 311 - 109­ ->

- PI 13-31 21-24 14-16 (­ f--18-)G­ >

-SPECIFIC GRAVITY

-VOlD RATIO 0.7)-0.78 0.55-0.61 0.&9-0.91 ( .'9­ ->

-lSATURATIOM 93-100 90-100 98-100 ( I-lOG­ ->

-MAX. DRY DEMSIT"t(TCl'I) 1.31-1.41 1.65-1.80 1.5:1 (­ 1.511-1.89 ->

-OPTIHU'H V.C. (q 29-]0 15.2.-16.2 21-23 11.:1-14.0

Table 2 Permeability Ranges

PERMEABILITY PROPERTIES

- KORIZONTAL '-h

RANCE (CIII./icc )

AVERAGB (clII./lec)

MLOHG PLUA!tC DAK HONe PU UI 0"" Ml.Jt;P3 ..,

., 10-5 TO

I , 10.3

2.:1 X 10- 4

NPL1.lfPU ,NPU

, , 10-6 TO

1.5 X 10.4

I. 2. X 10-6

.., , 10-6 TO

5.0 X 10-olI

:1.0 X 10-:1

- VEIlTICAL ,"v

RANCE (cm./sec)

AVERAGE (em.l.eel

:I.a x 10-6 TO

6.2. X 10-:1

3,0 X 10-:1

1. a x 10-6 TO

6.0 X 10-4

I. 0 X 10-4

, , 10-7 TO

I , 10-6

4.0 X 10-6

- PERKEABILITY RATIO

(1:'1: • I:h/l:v )

"'0£

AVDACB

2..1 to 1.:1

1.1

'.0 TO 7.0

,., ,.. TO 7.0

..,

Figure 1. Effects of compaction on soil structure (Lambe 1962)

Low compactive

effort

GRANULAR

High compactive effort

aD O lo)

. f'

B

\ r--'f

Molding water content >­

PRISMATIC

k

C=:=~~D ~

'" ===::>; 0 PLATY f

BLOCKY

Figure 2. Effect of particle shapes to horizontal and vertical permeabilities

2.8 Q

Q

5.6 Q

Seepage

~---

Downstr9m Jntl1

Impervious 'ound~\ion

Impervious foundation

Impervious lou"d.tioll

.::::==---­

Line of seepage !'or

kl/k~ - 100

R.hl-. ­ 50

k ...tk .. ­ 16

.,

I' I' b=O.4h

(0)

(b)

Wner surface

Core.,

---- --=- --_---:.

---~ -­ -

Figure 3. Effect of anisotropic embankment on drainage

requirement (Cedergren 1967)

}~~:,::.' f-+- b = 0.12 h

Figure 4. Effect of anisotropic core material on line of seepage (Cedergen 1967)

---------

-- ---

TOE DRAIN FILTER I

50

45

40

35

0 30

0: >='" 25> ~ -" 20

'" 15

10

5

o 1.34 1.36 1.38 1.4 1.42 1.44 1.46 1.48

\

-

~ \ ~\

'" "-­----....

'--...

r--­ -FACTOR OF SAFETY

Figure 5. Stability of dam slope affected by permeability ratio for toe drain

IHORIZONTAL DRAIN FILTER I

50

45

40

35

o 30 ~ 0: 25 > ~~...... ~ 20 .""'" I>.. I15

I

10

~ 5 --. "---.o

1.35 1.4 1.45 1.5 1.55 1.6 FACTOR OF SAFE'TY

Figure b. Stability of dam slope affected by permeability ratio for horizontal drain

~ IOlllpl__ 4­

lleel plat.

atl,.' plot.

lompl., ,,"

lilj.J~ 19 U'i::<iiu 2536

0.3111.

lob lIorl:rOf'ltol lomplln,g

l'lydrCluUe Jocll "O.3'"i'1-;-"

11 •• 1"" plol

Figure B. Schematic diagram of test set-up

lab Yer'lClll lampllng

/'mold , 0"

Figure 7. Samples preparation for horizontal and vertical

I SAMPLE KP:l. NPL-3 U ISAMPLE KPI. 2 NPL1.2 lJ I

~ORROW AREA \J I

I AELD COMPACTION ON DAM SITE IJ

\ LABORATORY COMPACTION U I INrlJAL PHYSICAL PROPERTY

GRADATION A~~ERG;AUMI~ENS'TY ~.~ e S SPG

I

\: DEAIRING 24 HRS~JJ SATURAllON 48 HR

I PERMEABILITY TEST

PRESSURIZE HEAD 10 TO eo m LOADING AND UNLOADING

T

INAL PHYSICAL PROPERTY TES=;:

DENSITY , WY. • GRADATION

IDATA ANLYSIS IJ

Figure 9. Testing procedure

CD ~

c-o 0

'-~

1.0E ~ " ,..

I ­:0 0 0

E 1.0"-= :­0­

o BORRe [W o<PJ .0. c.et.AP CTED FLL PU ~, 'uo"

r-­

1.0 >-06

25 35 45 55

LIQUID LIMIT. LL %

Figure 1O. Permeability versus liquid limit

--

52 11'l1n'i'ilJ'Il1'i lJn. lli lJ-vl 1 9 ,j'i~<i1tl 2536

u 1.0 ••.... E u

~

:0 c• 1.0E

0.•~

KP

Core zo e . hor.

"-4 , v er.

-r-::--:::--. - Avera " hor. r= 10.67 - --­ - -=F-­

E-5 --­- - .

average ve r. r = 0.78

E-6to

o 200 400 600 800

Hydraulic gradient (hill.

Figure 11. Permeability versus hydraulic gradient for soil in KP1 group

100

0-,--­~

10

1.0

-.

0.1

~~

- . - '--=-­

--...

KP

L-<.uPpo boundar Core z no

- - -- -.

--. - -

low-er b<: - ._-~- - - . ndory. QVIH

-

-­

= 0.1

o 200 400 600 800

Hydraulic gradient (HILl.

Figure 12. Permeability ratio for soil in KP1 group

1.0

•u~ 1.0 E u ,:.

D o•E• 1.0 a.

1.0

E-4

E-5

\

"'" ~

--

!!.': Con

-poct

-d fill

. 2.

- ./ _'ove ago r

~

ver. .... er.

• O.

0 0 r

00

unlo

B

--

• v. . -

d.

,0-...; '" - . --­ aver

E-G

."'-:­

-

-. .

No .:

-

12 Ns =

-.=

12

-

E-7

o 4 B 12 16 20 24

CYClE(rimes)

Firgure 1 3. Permeability variation with test cycles

100

/R, ndoo­ lon o(KP. "Com poeT d filll.(N Ll. 10

r

"' "­ ... va' -.... Com oe\ d 1j I 2.( PLI. Bor row.l NPU.

1.0

- -I---­ -_... - f--­

- .­ f--. ._­ -­ -Ns::: 12

0.1

o

o

o 4 B 12 16 20 24 2B

CYCLE (limes)

Figure 14. Permeability ratio versus test cycles

---

100

80

60

40

20

o

Diomef"r,mm.

0.0010.0001 10Ql0.01

""~ / I

in. , V

// I - ~ - V ./'

/, -- -- e--- ...- !

b to -- - V

I out. ' , 1--- '! ,/,c- e/

'l V I- " I [

/ ~ I

~ Bah

, ,Ii I ! i ,I I

I I , I i

Figure 1 5. Gradation change during permeability test.

10

9

B ,

,H~E 7 2­-[ 6 E ~ 5

:c 4 .'" ~

I 3

2

! I

COARSE (Gl)Ii I Ll --+­(",\ COARSE (G2)

COARSE (G3)Ll

II \ -­

\ -e­L2L2 FINE (G1)~ ~I --><­L3 FINE (G2)~ I -k-IL4 FINE (G3)I~

• [~ L3~

_ L4,\. \,\ f--­

a a 10 20 30 40 50 6070 BO 90 100

% Finer than # 200

Figure 1 6. Migration of particles smaller than 0.074 mm.