HORIZONTAL PERMEABILITIES OF COMPACTED SOILS · HORIZONTAL PERMEABILITIES OF COMPACTED SOILS....
Transcript of HORIZONTAL PERMEABILITIES OF COMPACTED SOILS · HORIZONTAL PERMEABILITIES OF COMPACTED SOILS....
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.