)
Soil Compaction
l n t h e c o n s t r u c t i o no f h i g h w a ye m b a n k m c n t se, a r t h d a m s ,a n d m a n y o t h e r e n g i n e e r ing structurcs,loose soils must be compacted to increasethcir unit weights. Compaction incrcasesthe strength charactcristicsol'soils.which increasethe bearing capacity of [oundationsconstructedovcr them. Compaction also dccreasesthe amount
o f u n d e s i r a b l cs e t t l e m c n to f s t r u c t u r c sa n d i n c r c a s c st h e s t a b i l i t yo f s l o p e so f e m rollers. shccpsfoot rollcrs, rubber-tired rollers, and vibankments. Smootl.r-wl'rccl
bratory rollers arc generally used in thc ficld for soil compaction. Vibratory rollers
arc uscclmostly for the densificationol'granular sclils.Vibroflot devicesare also used
frtr compacting granular soil depositsto a considerzrblcdepth. Compaction of soil in
this manner is known as vihntflotutioz. This chapter discusscsin some dctail the
p r i n c i p l e so f ' s o i l c o m p a c t i o ni n t h e l a b o r a t o r ya n d i n t h e f i c l d .
5.1
Compaction-
General Principles
Compaction, in gencral, is the dcnsificationol'soil by removal of air, which requires
mechanicalenergy.Thc degreeo1compactionof a soil is measuredin terms of its dry
unit weight. When water is addcd to the soil during compaction, it acts as a softening agent on the soil particles.The soil particlcs slip over each other and move into
a denselypacked position.The dry unit weight after compaction first increasesas the
m o i s t u r ec o n t e n ti n c r e a s e s(.S e eF i g u r e5 . 1 . )N o t e t h a t a t a m o i s t u r ec o n t e n tw : 0 ,
the moist unit weight (7) is equal to the dry unit weight (7,,),ot
7
:
|t(r-.tt:
7l
When the moisturc content is gradually increasedand the same compactiveeffort is
usedfor compaction,the weight of the soil solidsin a unit volume graduallyincreases.
F o r e x a m p l e .a t w : t ' 1 ,
f :7:
However, the dry unit weight at this moisture content is given by
f ,tr,,,, 1:
100
1 a 1 , ,' , ,
tr 17,1
5.2 Standard Proctor Test
101
"{z
J
,:!
.:
'5
> .: 7l
. l
= l
F I
l t l
- l
> l
l
t
l
>-l
Moisturc
contentr,
Figure 5. I principles of compaction
B e y o n da c e r t a i nm o i s t u r cc o n t c n t w : w t ( F i g u r e- 5 . 1 )a, n y i n c r c a s c
in thc moisture
c o n t c n t t e n d s t o r c d u c e t h e d r y u n i t w e i g h t .T h i s p h e n o m e n o n
o c c u r sb c c a u s ct h c
w a t e r t a k e su p t h c s p a c e st h a t w o u l d h a v c b c e n o c c u p i e db y
t h c s o l i c lp a r t i c l c s .. l - h c
m o i s t u r ec o n t e n t a t w h i c h t h e m a x i m u m d r y u n i t w e i g h t i s
a t t a i n e di s g e n c r a l l yr e ferred to as the opfimum moisturc content.
T h e l a b o r a t o r yt e s t g e n e r a l l yu s c c lt o o b t a i n t h e m a x i m u r r
dry unit weightof
compaction and thc optimum moisturc content is called the Proctor
t'ctntput'tipntest
(Proctor, 1933).The procedurefor concluctingthis typc of test
is describeclin the lbllowingsection.
5.2
Standard Proctor Test
In the Proctor test,the soil is compactedin a mold that hasa volune
o1'944cmr (.1ift.).
T h e d i a m e t e r o f t h e m o l d i s 1 0 1. 6 m m ( a i n . ) . D u r i n g t h e l a b o r a t o r y
t e s t ,t h e m o l d
is attached to a baseplateat the bottom and to an extensionat
the tqp (Figure 5.2a).
The soil is mixed with varying amounts of water and then compacted
in three equal
layers by a hammer (Figure 5.2b) that delivers2,5blows to each
layer.The hammer
has a massof 2.5 kg (5.5 lb) and has a drop of 30.5mm ( r2 in.).
Figure -5.2cis a pho_
tograph of the laboratory equipment required for conducting
a standardproctor test.
For each test, the moist unit weight of compaction! can be
calculatedas
7,
,' :
*
V,,,,
where 14/: weight of the compactedsoil in the mold
(,,y : volume of the mold 1944cm3 (rafC)]
(-5.1
)
t
102
Chapter 5
Soil Compaction
I
I 1 4 . 3m m
diameter
(4.5 in.) --*l
I
bxtensron
;€=::==:::::-:
t'.'
l. I
r r .r j
DroP=
304.8nm
(l2in.)
(a)
W e i g h to f
harnmer= 2.5 kg
( r n a s s- 5 . 5 l b )
l.-l
5 0 . 1m
1m
(2 in.)
(b)
(c)
Figure 5.2 StandardProctortest equipment: (a) mold; (b) hammer (c) photograph of laboratory equipmentusedfor test
5.2 Standard Proctor Test
\25
Zeroair-void
curve
(G' = 2.69,
19.0
120
E
l 8 . sz
a
Maximum 1.,
il
J
| l-)
l a i . lI d
.E
o
1 7 . . 50
r0-5
5
Optimum
n.lolsture
contcnt t
t0
l-5
Moisturecontent,w (%)
tu
Figure 5.3 Standard Proctor compaction test results for a silty clay
For each test, the moisture content of the compacted soil is determined in the laboratory. With the known moisture content, the dry unit weight can be calculated as
r u -_ $ 6
t-
( s.2)
1oo
where w ("/") : percentageof moisture content.
The values of 7,1determined from Eq. (5.2) can be plotted againstthe correspondingmoisture contentsto obtain the maximum dry unit weight and the optimum
moisture content for the soil. Figure 5.3 showssuch a plot for a silty-claysoil.
The procedure for the standardProctor test is elaboratedin ASTM Test Designation D-698 (ASTM, 1999)and AASHTo resr DesignationT-99 (AASHTO, 1982).
For a given moisture content w and degree of saturation $ the dry unit weight
of compaction can be calculatedas follows: From chapter 3 [Eq. (3.16)],for any soil,
,., :
where G" : specific gravity of soil solids
7,, : unit weight of water
e : void ratio
G'f''
l + e
104
Chapter 5
Soil Compaction
a n d ,f r o m E q . ( 3 . 1 8 ) ,
Se : G,rl
or
G,trr
- . s
Thus.
Grlr,
i /
Id
(s.3)
: -
Glo
t*
I
s
I
Fgr a given moisture content, the theclreticalmaximum dry unit weight is obt a i n e dw h c n n o a i r i s i n t h c v o i c ls p a c es - t h a t i s ,w h c n t h e d c g r e eo f s a t u r a t i o ne q u a l s
l 0 g % . H c n c e , t h c m a x i m u m d r y u n i t w c i g h t a t a g i v e n m o i s t u r ec o n t e n t w i t h z e r o
a i r v o i d sc a n b e o b t a i n e db y s u b s t i t u t i n gS - I i n t o E q . ( - 5 . 3 )o. r
rzu,,:
#*:
-rT
'
(s.4)
w + G..
where y-,^.: 7.ero-air-voidunit weight.
To obtain thc variertion of 7.,,,.with moisturc content, use the following
proccdure:
1.
2.
3.
4.
Determine the specificgravity of soil solids.
Know the unit weight of water (7,,,).
Assume severatlvaluesof w, such as 57o, 10"/",15"/",and so on.
I-JseEq. (-5.a)to calculatey r,,,,f or various valucs of w.
Figure 5.3 also showsthe variation of 7.u"with moisture content and its relative
location with respectto thc compaction curve. Under no circumstancesshould any
part of the compaction curve lie to the right of the zero-air-voidcurve.
5.3
|I
Factors Affecting ComPaction
The preceding section showed that moisture content has a strong influence on the
degree of compaction achievedby a given soil. Besidesmoisture content, other important factors that affect compaction are soil type and compaction effort (energy
per unit volume). The importance of each of these two factors is describedin more
detail in the followins two sections.
5.3 FactorsAffecting Compaction
Iu.u6
S a n d ys i l t
t8.-50
Iu.(x)
,P
!
E
z
Siltyclay
l7 <rt
s
._.
.zr I il)
J
s
H i g h l y p l a s t i cc l a y
'a
'E
E
'| 7' 't r' t'r =
Poorly gradcdsand
r05
I6.-50
r6.(x)
l (X)
5
Figure 5.4
t0
l-5
M o i s t u r cc o n t c n t , r . ( ? )
'I'ypical
15 . 7 a
20
conrpaction curves li)r lirur soils (AS.l.M D_69u)
Effect of Soil Type
'l'he
soil type - that is, grain-sizedistribution, shapeof the soil grains,specilicgrav_
ity of soil solids,and amount ancl type of clay minerals p."r.ni- has a grcat
inllu_
c n c e o n t h e m a x i m u m d r y u n i t w e i g h t a n d o p t i m u m m o i s t u r e c o n t e n t .F i e u r e
5.4
showstypical compaction curvesobtained lrom lirur soils.The laboratory teits
were
conducted in accordancewith ASTM Test Designation D-691t.
Note also that the bell-shapedcornpactioncurvc shown in Figure ,5.3is typical
of most clayey soils. Figure -5.4sh'ws that for sands,the dry unit ,i,eighthas
a general tendencylirst to decreaseas moisture content increases,and then to increase
to
a maxinlum value with further increaseof moisture. The initial decreaseo1
dry unit
weight with increaseof moisture content can be attributed to the capillary
tension
effect.At lower moisture contents,the capillary tensionin the pore water inhibits
the
tendency of the soil particles to move around and be denselvc'mnacted.
Lee and Suedkamp (1912)studieclcompactioncurvesfbr 35 soil samples.They
observed that four types of compaction curves can be found. These curves are
shown
in Figure 5.5.Type A compaction curvesare those that have a singlepeak.
This type
of curve is generally found tbr soils that have a liquid limit betweJn 30 and 70.
Curve
type B is a one-and-one-half-peakcurve, and curve type c is a double-peak
curve.
F
106
Chapter 5
Soil Compaction
@
o
M0isture content,t|'
Figure 5.5 Typcsof compaclion curvc
Compaction curves of types B and C can be found for soils that have a liquid limit
lessthan about 30. Compaction curves of type D do not have a definite peak. They
are termed odd shuped.Soils with a liquid limit greater than about 70 may exhibit
compaction curvesof type C or D. Such soils are uncommon.
Effect of Compaction
Effort
The compaction energy per unit volume used for the standardProctor test described
i n S c c l i o n 5 . 2 c a n b e g i v e na s
..(,*"In")
(,)T*:)
, (,*:i''),
(iTJ:?)
E :
\p", tny"r/
\ tuy.r,,/
\t.,o*,n"r/
\ nut,n"r 7
Volume of mold
(s.s)
or, in SI units,
(2s)(3)
(%p
E :
-)
r.N)to.:os
944> l0"mj
: 594kN-m/m3: 600kN-m/m3
In Englishunits,
E -
/J5t)*r l)t
\/ L7Js) \\J1- t1: J) :5
:
D375 ft-lb/ft3 :
l 2 . 4 t J 0f t - l b / f t r
i r \
\30i
If the compaction effort per unit volume of soil is changed, the moisture-unit weight
curve also changes.This fact can be demonstrated with the aid of Figure 5.6, which
shows four compaction curves for a sandy clay.The standard Proctor mold and hammer were used to obtain these compaction curves. The number of layers of soil used
for compaction was three for all cases.However, the number of hammer blows per
each layer varied from 20 to 50, which varied the energy per unit volume.
5.4 Modified Proctor Test
ttJ
19.85
Sandyclay
L i q u i dl i n i t = 3 1
P l a s t i cl i m i t = 2 6
Line of
optlmum
E
i
rr<
E
.E
: ll0
107
19.00
in k
E
z
3
Ir,i.00
;
.s!
')
.=
=
q
\,2-5 blows/ layer
17.(x)
2 0 b l o w s /l a y e r
t0
12
t1
16
It {
2(\
Moisturecontent,11,
(.2,)
22
24
Figure 5.6 Effect of compaction cnergy on the compaction of a sancryclay
From the preccding observation and Figure 5.6, we can see that
l. As the compaction effort is increascd,the maximum drv unit weight of compaction is also increased.
2. As the compaction effort is increased,the optimum moisture content is decreasedto some cxtent.
The preceding statementsare true for all soils. Note, however, that the degree of
compaction is not directly proportional to the compaction eftbrt.
Modified Proctor Test
With the developmentof heavyrollers and their usein field compaction,the standard
Proctor test was modified to better represent field conditions. This revised version is
sometimesreferred to as the modified Proctor /esl(ASTM Test Designation D-1557
and AASHTO Test Designation T-180). For conducting the modified proctor test,
the same mold is used with a volume of 944 cm3 (1/30 ft3) as in the caseof the standard Proctor test. However, the soil is compacted in five layers by a hammer that has
a massof 4.54 kg (10 lb). The drop of the hammer is 457 mm (1s in.). The number of
hammer blows for each layer is kept at 25 as in the caseof the standard proctor test.
7
108
Chapter 5 Soil Compaction
The compaction energy for this type of compaction test can be calculated as
2700 kN-m/m3 (56.000ft-lb/lbr).
Becauseit increasesthe compactivceffort, the modifieclProctor test resultsin
an increasein the maximum dry unit weight of the soil. The increasein the maximum
dry unit weight is accompaniedby a decreasein the optimum moisture content.
In the precedingdiscussions,the specificationsgiven for Proctor testsadopted
by ASTM and AASHTO regardingthe volume of the mold and the number of blows
are gcnerally those adopted for fine-grainedsoils that pass through the U.S. No. 4
sicve.However, under each test designation,there are three suggestedmethods that
reflectthe mold size,the number of blows per layer, and the maximum particle sizein
a soil aggregateusedfor testing.A summary of thc test methods is givenin Table 5.1.
ol StandardanclModificdProctorCompaction
Table5.7 Sunrn.rary
(ASTM D-69,S
and D-1557)
TcstSpecifications
Method A
Description
PhvsicalData
lor rhc'l'ests
Standard
Proctor Test
Modified
Proctor Test
Method C
Method B
Matcrial
PassingNo. 4 sicvc
Passing9.,5mnl
( I in.) sicvc
Passing19 mm
( ] in.) sieve
Lisc
Ljsed if 207u or lcss
by wcight ol rnatcrial
i s r c l a i n c do n N o . , l
( 4 . 7 5r n m ) s i c v c
Ljscd il'more than 207"
by wcight ol'material is
r c t a i n c do n N o . 4
(4.7-5
r n m ) s i c v ca n d 2 0 % ,
or lcssby wcight o[
nratcrial is rclaincd on
9 . - 5r n r n( i i n . ) s i e v e
Ljscd if morc tl.ran20'l"
by wcight of matcrial
i s r e t a i n c do n 9 . 5 m m
( l i n . ) s i c v ea n d l e s s
than 30% by wcight of
material is rctaincd
o n 1 9m m ( I i n . ) s i e v e
Mold volurnc
944 crnr ( ..1,ltt)
944 crnr ( + ftt)
944 crnr ( ; l1t)
Mold diamctcr
1 0 1 . 6m m ( 4 i n . )
1 0 1 . 6m m ( 4 i n . )
1 0 1 . 6m m ( 4 i n . )
Mold hcight
1 1 6 . 4m m ( 4 . - 5 t ti4n . )
1 1 6 . 4m r n ( 4 . . 5 1 i3n4. )
I 1 6 . 4m m ( 4 . - 5 1itn, 1. )
Wcight ol'
hammer
24.4 N (-5.5lb)
24.4 N (5.5 tb)
24.4 N (-5-5lb)
Heightol drop
3 0 5m m ( 1 2 i n . )
3 0 5 m n r ( 1 2i n . )
3 0 5m m ( 1 2i n . )
Numberof
soil laycrs
3
3
3
Number of
blows/laycr
25
25
56
W e i g h to f
hammer
4 4 . 5N ( l 0 l b )
44.-5
N (l0lb)
4 4 ' 5N ( 1 0 l b )
Height of drop
457 mm (18 in.)
457 mm (18 in.)
'157mm (1t3in.)
Numberof
soil layers
5
5
,5
Numbcr of
blows/layer
25
25
56
5-4
Modified
Proctor Test
109
Example5.1
For a compacted
soil,G" : 2.72,w = 187o,andya : 0.97rn. Determinethe dry
unit weightof thecompacted
soil.
Solution
FromEq.(5.4),
Tzo'':
9.81
;=*:17.9
--JU,-"
,,+
I
G,
16
1
100
2.72
kN/mr
Hence,for the compactedsoil,
- 16.tkN/m3
t,r = 0.91,u,: (0.9)(17.9)
Example5.2
The laboratorytestresultsof a standardProctortestaregivenin thefollowingtable:
Volume
of mold
(fr3l
Weight of moist
soil in mold 0b)
Moisture
content, u/
(V"l
3.63
3.86
4.oz
ih
,l
$
10
t2
14
+
3.e8
16
*
3.tts
18
Determine the maximumdry unit weightof compactionand the optimum moist.urecontent.
Solution
The following table can be prepared:
Volume of
mold,V
(ft3l
I
I
l0
,L
30
I
30
I
30
1
l0
Weight of
sgi!W
Moist unit
weight,y
ilb)
[bltfy'
3.63
3.86
4r))
3.98
3.88
3.73
"y=WV
oto = ylll +
[w (%)i100]]
108.9
115.8
120.6
119.4
116.4
111.9
Moisture
conrent,w
to/"I
10
IL
I4
16
18
20
Dry unit
weight,76
truTrtdl;
r 99.0
fuo:.+
,105.8
142.9
98.6
93.3
110
Chapter5
Soil ComPaction
.E
lt,l
=
;
t
.1D loo
E
o 9 5
90
."n
l0
16
14
t2
'r'({./.')
contcnt.
Moisture
llt
20
Figure 5.7 Moisture content, w (%)
is shownin Figure5,.7.From the plot, we seethat the maxThe plot of 74versusr.r,'
imum dry unit weight (7ar-""1): 106lb/ft3 and that the optimum moistureconI
tent is 14.4"/".
5.5
Structure of Compacted ClaY Soil
Lambe ( l95u) studied the cfTecto1 compaction on thc structure of cliry soils,and the
If clay is compactcd with zrmoisture
resultsol his study arc illustrateclin Figure 5.11.
r
e
p
r
c s e n t c db y p o i n t A , i t w i l l p o s s c s su r
a
s
o
p
t
i
m
u
m
,
o
f
t
h
c
contcnl on the dry sidc
because,at low moisture content.
results
o[
structure
type
flocculent structure.This
clay particles cannot be fully dethe
ions
surrounding
of
the dilTuscclouble layers
This reduccd repulsion rcsults
is
rcduced.
rcpulsion
velopecl;hence,the interparticle
unit weight. Whcn the moisdry
a
lower
and
particle
orientation
in a more random
point B, the diffuse double
by
as
shtlwn
is
increascd,
turc content of compaction
repulsion between thc clay
the
increases
which
particles
cxpand,
layers arounclthc
dry unit weight. A cona
higher
and
flocculation
of
degree
particlesand givesa lowcr
the
double laycrs more.
B
to
C
expands
from
content
tinued increasein moisture
the particlesand
between
of
repulsion
increase
continued
This expansionresultsin a
less
dispersedstrucor
a
more
and
particlc
orientation
of
thus a still greater degrce
water
dilutes the
the
bccause
added
decrcases
weight
ture. However, the clry unit
per
volume.
unit
concentration of soil solids
At a given moisture content, higher compactive effort yields a more parallel
orientation to the clay particles, which gives a more dispersedstructure. The parlicles are closer and the soil has a higher unit weight of compaction.This phenomenon can be seenby comparing point,4 with point E in Figure -5.8
Figure 5.9 showsthe variation in the degree of particle orientation with molding water content for compacted Boston blue clay.Works of Seed and Chan (1959)
have shown similar results for compacted kaolin clay.
!
E
High
compactive
effort
E
U
Low
compactive
effort
M o l d i n g w a t e rc o n t e n t
Figure 5'8 Effect of compaction on structurc of clay soils (re<Jrawnafter Lambc, l95tj)
t00
Parallel
c
a
o
-50
r
25
o
l0
t2
t4
l8
24
ll4
ll0
1 7 . 0 0^
E' t06
z
J
.d t{)2
l/. On ;
, il6
.:tr
= 9 8
Higher compactionenergy
Lower compactionenergy
94
l0
t2
14
16
l8
15.005
t4.14
20
22
24
Molding moisturecontent(7c)
Figure 5.9 Orientationagainstmoisturecontentfor Bostonblue clay (after Lambe,1958)
111
112
Chapter 5
I
t-
Figure 5.70 Srnooth-whcclrollcr (coultesy ol'Davicl A. C'arroll.Austin. Texas)
,*x"\
rubber-tircdnrller (courtesyof DavidA. Carroll.Austin,Texas)
Figure 5. 11 Pneumatic
112
5.6 Field Compaction
5.6
113
Field Compaction
Compaction
Equipment
Most of the compaction in thc field is done with rollers.The four
most common types
of rollers are
l.
2.
3.
4.
S m o o t h - w h e e rl o l l e r s( o r s m < t o t h - d r u m
rollers)
P n e u m a t i cr u b b e r - t i r c dr o l l c r s
Sheepsfootrollers
Vibratory rollers
S m o o t h - w h e crl o l l e r s( F i g u r e. 5 . 1 0a) r e s u i t a b l cf o r p r o o f r o l l i n g
s u b g r a d e sa n d
f o r l i n i s h i n go p e r a t i o no f f i l l sw i t h s a n d ya n c lc l a y e ys o i l s .T h e s e
r o l l e r sp r o v i d e 1 g 0 %
c o v e r a s eu n d c r t h e w h e c l s .w i t h g r o u n dc o n t a c tp r e s s u r e a
s s h i g h a s3 1 0t g 3 u 0k N / m 2
(4-5to -5-5
lb/inr). They.arc_norsuirablc lirr producing high un'it weights
of compac_
t i o n w h e n u s e c cl t nt h i c k e r l a v e r s .
P n c u m t r t i cr u b b c r - t i r e c rl t r l l er s ( F i g u r c - 5 . 1 1a) r e b c t t c r i n m a n y
r e s p e c t st h a n
t h c s r n o o t h - w h c crl t l l l c r s .l ' h c l i r r m c r a r e h e a v i l yk r a d c dw i t h
s e v e r a lr o w s o f t i r e s .
'fhcse
lircs are closcly spacecl- I'our to six in a row. T'hc contact pressure
undcr the
t i r c s c a n r i t n s |er o n t 6 ( X ) t o 7 ( X ) k N / m r ( t l - 5l ltxo) l b / i r r 2 ) , a n c l
theyproduceaboutT0
to lJ0'Z'covcrage.Pncunralic rollers can be used lirr sanclyancl
.t,iy"y soil compaction. c-'ompaction
i s a c h i c v e cbr y a c o r n b i n a t i c l n
o | p r . r r u r " a n c lk n e a d i n ga c t i o n .
Shcepsli*rt r.llcrs (F-igurc.5.l2) arc drunrs with a large number
.f projections.
The arca .l'c.ch pro.icctionmay rilnsc ll-.rn 2-5t. g5 cm2( j + to
l3 i'2). Theserollers
.,..,,:l:,..,,
..,,:-
.,.
.
Figure 5' 72 Sheepstootroiler (courtesyof David A. Carrolr,Austin,
Texas)
114
Chapter 5
Soil ComPaction
Ofl'-center
rotating
weight
-Vibratof * - -
(hr
*H'**
OfI'-center
rotating
weight
Figure 5. 13 Principlesof vibratory rollers
are most effective in compacting clayey soils. The contact pressure under the projections can range from 1400to 7000kN/m2 (200 to 1000Ib/in2).During compaction
in the field, the initial passescompact the lower portion of a lift. Compaction at the
top and middle of a lift is done at a later stage.
Vibratory rollers are extremely efficient in compacting granular soils. Vibrators can be attacheclto smooth-wheel,pneumatic rubber-tired, or sheepsfootrollers
to provide vibratory effectsto the soil. Figure 5.13demonstratesthe principles of vibratory rollers. The vibration is produced by rotating off-center weights.
Handheld vibrating plates can be used for effective compaction of granular
a limited area.Vibrating platesare also gang-mountedon machines.These
over
soils
plates can be used in lessrestricted areas.
Factors Affecting
Field Compaction
ln addition to soil type and moisture content, other factors must be consideredto
achievethe desiredunit weight of compaction in the lield. These factors include the
thickness of lift, the intensity of pressure applied by the compacting equipment, and
the area over which the pressure is applied. These factors are important becausethe
pressure applied at the surface decreaseswith depth, which results in a decreasein
the degree of soil compaction. During compaction, the dry unit weight of soil is also
affected by the number of roller passes.Figure 5.14 shows the growth curves for a
silty clay soil. The dry unit weight of a soil at a given moisture content increasesto a
certain point with the number of roller passes.Beyond this point, it remains approximately constant. In most cases,about 10 to 15 roller passesyield the maximum dry
unit weight economically attainable.
Figure 5.15a shows the variation in the unit weight of compaction with depth
for a poorly graded dune sand for which compaction was achieved by a vibratory
drum roller. Vibration was produced by mounting an eccentric weight on a single rotating shaft within the drum cylinder. The weight of the roller used for this compaction was 55.6kN (12.5kip), and the drum diameter was 1.19m (a7 in). The lifts were
kept at 2.44 m (8 ft). Note that, at any given depth, the dry unit weight of compaction increaseswith the number of roller passes.However, the rate of increase in unit
5.6 Field Compactian
115
t8
Moisture content= l7
l7
M o i s t u r ec o n t e n t= I 1 . 6 7 c
16e
z
g
15 .-t
ti
j
{
'0
'4o
t4>
)
c
t
l l n
Silty clay
Figure 5.14
Growth curves for a silty clay * relationship
between dry unit weight and number ofpassesof
U4.5kN (19 kip) three-wheelroller when the soil
is compactedin229 mm (9 in) toose layersat different moisture contents(redrawn after Johnson
and Sallberg, 1960)
l2
L i q u i dl i m i t = . 1 3
P l a s t i c i t yi n d e x= l 9
r l l
rJ
^ t00
t,-
t6
24
Number of roller passes
Dry unit weight,y,1(lb/fi:.y
t04
1a
lt'8,
,r.ttt,
Relative density, D,. (%)
^,, 5o
"ut_r,
60
70
|1{)
Relative density, D,. (o/o)
9Q,
0.0P
60
-E--U
10
80
90..
0.50
0.5
E
'l '{ - X l
A
a
I
I
Curnpaetitrn lticr
5 roller passes
€ e
E
o r
r r
o r.v
- ; : _ .
E
;: t.u
Nurnberof
rollerpasses
r6.00
16.50
Dry unitweighr,
17(kN/m:.t
+
0.5
2
t.5
l.)
1.83
l .83
0.46
(l8 in.)
I
I
2
3 €
o
r.83
17.00
(a)
Figure 5.15 (a) Vibratory compactionof a sand-variation of dry unit weightwith number
of roller passes;
thicknessof lift : 2.45m (8 ft); (b) estimationof compactionlift thickness
for minimum requiredrelativedensityof 75"/"with five roller passes(ifter D,Appolonia,
Whitman,and D'Appolonia, 1969)
116
Chapter5
Soil ComPaction
weight gradually decreasesafter about 15 passes.Another fact to note from Figure 5.15ais the variation of dry unit weight with depth for any given number of roller
passes.The dry unit weight and hence the relative density,D,, reach maximum values
at a depth of about 0.5 m (1.5 ft) and gradually decreaseat lesserdepths. This decrease occurs becauseof the lack of confining pressure toward the surface. Once the
relationship between depth and relative density (or dry unit weight) for a given soil
with a given number of roller passesis determincd, estimating the approximate
thickncssof each lift is easy.This procedure is shown in Figure -5.15b(D'Appolonia,
W h i t m a n , a n d D ' A P P o l o n i a .1 9 6 9 ) '
5.7
Specifications for Field Compaction
In most specificationsfor earthwork, the contractor is instructed to zrchievea compacted field dry unit weight of 90 to 9-5%of the maximum dry unit weight determined in the laboratory by eithcr the standard or modificd Proctor test. This is a
specificationfor relativc compaction,which cernbc expressedas
fi(%)=
7'1(Ii"r'r)
x100
(-s6)
7d(rnax * lab)
For the compaction of granular soils, spccificationsare sclmetimeswritten in
terms of the required relativc density D, or thc required relativc compaction. Relative density should not be confused with relative compaction. From Chapter 3, we
canwrite
a:l
(-57)
. c s e et h a t
C o m p a r i n gE q s . ( - 5 . 6a) n d ( . 5 . 7 )w
R *
Ro
1-D,(1-Ro)
(s.8)
where
Ro:
711(nin)
1 5q \
7rl(max)
on the basisof observationof 47 soil samples,Lee and Singh (1971) deviseda
correlation between R and D, for granular soils:
R:80+0.2D,
(s.10)
5.7 Specifications for Field Compaction
117
.3t
i
E
o
4r
r'l
t,,,rt,,."
.,,,,,i11.
,,
Figure 5.76 Mostcconornical
contpaction
condition
The specificatior for field compacticlnbasedon relativc compaction
or on rel'l'hc
ative density is an cnd-product specificaticln.
contractor is expectedto achievea
rninimurn dry unit wcight regardlesso1'thc field procedure
ad'pied. The most eco_
n o m i c a l c o m p a c t i o nc o n c l i t i o nc a n b c e x p l a i n c dw i t h t h c
a i d o f F i g u r e 5 . 1 6 .T h e
conrperctioncurvcs A,B, and C arc for thc same soil with verrying
compactiveeffort.
Let curve ,4 rcprcsent the conditions of ntaximum compactive
eifort that can be obt a i n c d f r o n l t h e e x i s t i n ge q u i p m e n t .L e t t h e c o n t r a c t o rb e r e q u i r e d
t o a c h i e v ca m i n imum clry unit weight of 7,r(ri"ru)
- R7,r1n,"*,.
To achievcthis, the conrracror must ensure that the moisture content r.r,falls between w, and w2.
As can be seen from
cornp.ction curve c, the requirccl
can be achieveclwith a lower compactiveef7,r1ri"ra1
fort at a moisture c()nten1|| : wt. Howcver, for most practical
conditions, a com_
pacted field unit weight o[ 7,i16"ray
: Ry,r1n,u,,
cannot be achievedby the minimum
compactive effbrt. Hcnce, equipment ivith slightly more than
the minimum competctiveeflbrt should bc used. The compaction curve B represents
this condition.
Now we can see from Figure 5.16 that the most economicalmoisture
content is between w3 and wr. Note that || : wt is the optimum moisture
content for curve ,4,
which is for the maximum compactiveeftbrt.
The concept described in the prece<lingparagraph, along
with Figure 5.16,
is historically attributed to Seed (1964), who was a giant in
modern geotechnical
engineering. This concept is elaborated on in more detail in
Hortz and Kovacs
(re81).
Table 5.2 givessome of the requirementsto achieve95-to-100%
relative com_
paction (basedon standardproctor maximum dry unit weight)
by various field com_
paction equipment (U.S. Department of Navy, 1971).
EFe!^ , 4,
' !
iEq,
F
F
>.=
q, 1
Pa,
-
C ) . -
a
z!s
c
6
6
-
ct
o)
o
'6
'i,
' - ? + =e - !
' ' e' - ' 3
€8
€3 EA1
- €8
* i . z n : - . 2 1 . , 2 | ; .1 :
=
.i 5-s\ i-t rr +
- -x -. i+' r; F- j, -=-A- Y 2 E o ^
'i.?
Z.i
B
3
X
6
a
!
G
th
lO'--
o
o
o
o 3
o >
o -
e E
o
_
5F
T I
f,i
v . -
o-E
f
+"Y
^ ^ ^ ( J
w - , c
&t
'c&
' = i iP
!:S
>i>-
tlE
2
t r! r- -; g. ?; .
!27=.
VtV6e;Ei^
zEi
:= != *2 <2
iPg
r!E=izzL
azZ;Ft
4+';=
Zfig.;?,9r^
| g E ' =7 2 l l ;
6
O
bo
t
5o
^
9
6 : ' 0
r .
J
-
6
9 . 9 = -
o o r 9 : J l 9 6 t . : 9
E 3 t y Z V1 1 a ;
E :"
a .E=t . =:" iA so o 3:
G O ! . =
L ' o
a ) o
: -
a i
)
f
E
D
>
,
d
E 9 : ; \ E
2 -
r
q
O
ho
\
o
o
^
e
T
t
s
U
- >^
o
o E *
; u
r) \o
; ; : I E ^ IF F E I F , , E = * : !I a E
118
,zz4=il22*:7i
E a
E 9 a " i 6 - " E ; : r
3 " P o . e : ' Fa i Z d
|lJ
^
< : . e 9 ,a E ; - q 5 I € F
2 V i '
a a * - : F = o - o . , =
o
t r o
!+ >.
-
y , ! : 2 =. =7o_ -a1= V= . 7= =l r i _' E
VE
:
. eg 6 in.= * F
6 o F z t A H i S !
0
*
F d =
E E 9€FF E I E E E i S
C
,
ro
o
a
.G
. r 9 * E -
= = _ . =
FEE
N
- 0 - 6 . l - , a U ' 4 L r '
E a !) 717' i =- 5 z: 6 E. { =e l Z
E
g
o
o
S
a
iS{. pq f: E A
Z ==ta Fs fFl r; B.
a €I E
=
2
6
ii. c-i a
.=
E
o
G
h
; ; ; o ; ; i E * zE ; E EE s r E g E E Z
Q)
o
€=
sL
! _
;g
o
J
D
l q ' a
'36? 2i '
=+Z'
E E
o
o
==
??
eissi
F X
E
8<. ;:
:is3:
H =
g.E
t
'=.:- "='l
E.= F.=
c ?:
o)
\ o P
o,='
e (1,
(
-t oFv T
' =l -sOp- i; U
: . =
- . ;. d
9 1. lt r! i=
(!
o
o
o
a
Fg::ETE=8b;g
!F!E*?? :Tt ?
t
=
:
F
,
i
E
i
l
i
:i:;;i:;A,E
6'
bo
c
:
0
) i , ?
& E g s : € ! ; r L : Ei e g
o-
-
:
t r
;::i+iie::E:=E:
F = : E : ? i E R e EzE5 * Z
tQc
+
=
ii
E= E#i g = r ;E
o
o.
o
t
i :
9!€ir;$o:i:E4-n
6
O P
- :
x x
_
*
N
^
J
- A O
. ,
L
o : 9
' eA ' 26
a A o
t- ' .;- oi
Ea 6> -.g E -_ 3
! i o -" :Y F : - ! o
' ) E j
= : . 0 ,
.- =- a / ' .
r_
c , q c - i ? . o
6 . - i U G q
I ]
. =
q- J> l a
_._
b
\
-"
^
-
O
a
O
z = 2 =+ i : F
o ' = :
ti;=
Q
a
.)
;'o
-
!
^
o
s
I
3
i : . u
6o=2
.-:
r j a
> y!=
g$iiigglg
gg
fi*iiig;giir
^
-
F
^ ! t r
-;i-
v
' U X o
>6to
t
z
r
: , ^ ^ u
o : l x =
: ^.a Y
; o
e ^
o :
@
i
O c B _
b.l)
6 : Z
-
,
*
c
q
!
:
q
-
L
l
'pjjU
f Fcn s
.LAr)ar
E U r o .
-
c Y . 3 a
. l i i 9 F b 0 5 n
E
v
l
E
F
U
^
-
a
a
^
o a
&'c3
U
oo
L
L
: b o
u
tr o-
p
N
. !
a
- 9
-
-
^
'
o._
, o
b0_
^
-
z*E
6 c ,
aD:!
t
bo
6
!
O
(d
bo
bo
O
9 >
c.)o
.-:
trN
l',
-O : E^ . _
a
i
^
^
:
x x
o ) F . )
t r ' t
^
C r ) r ,
N N =
I
C
:
E , Fe
Ir E
* : a
, i E a €
o - . = : i
-
+ = d E E
!
^
J
=
o * 3
o
o
w
t
Eg;*:
2
J
L
- a a 7 , . a
6 = 2 > =
E : d
i:;r
a
. 5 i = : t r
,
o
F . s; ;
i
?
c
t rh
I :
v S i d
o E \ o = L i ^ q d
! E ^ ' F , , . ; y ' E
: - j X Y
N - 3
i8s
;
;
t
N
o E €
- - -
=
q
;
-
(!
^
c
l
-
!
t
-
>
0
,
0
n
'E
co
u Z . E d i
- - ^ t r : l
C '
.Eq e g i
ac
Y
oo
6
!
^
^
p
6
>
> . ! " . : ; 1
d
6 Z
a
>,
- !\ . o
O
-
-
^ .
": crtr
I
L
^
r d
A J
5 - U
a
P
d €
7* z^
l
- c
hoi
I
a
2
h
i ' -
Z u ; 7
'i:
z
o
ca
v
E . , - - *
,
h E ?
9.Y co H
:Eco ai
v
- - : v : -" '
9
L
C
'
Y
=
^ = i
i
qo -; : cX i u
p d * ^
Y
7^2
k
or)
^
i.
-
C,^
7, a
i:
.9 v|E
Y Z E ' : -,
Ylz 9 1 , ^ c d€
r
O
E
9 a d s
E 4J >'.9
!
= v o
d
-
^
, F r - a >
6
t
Y
E
5
-?=: €. i Fn =t . i
< 6 b E > 5 0 3 € 5
6 1
-S
! 'o t
Eor u.!i:
8:'a
H oo'o
'E
; -o6 ^
d
r
X
5Fz€5s;
s € _ g E e9 g
F
f r ; 8 9 ;i F
?.-z t os!3
t j
h i
^
Y3
-c * aoJ
o
gc
Ut
di cr
F
^ ^
5
f i ; 3 ." t& r z E
e,,Y
: i iiT6
q Y o - o 9 B
.oER^6 >,
; ;; e= 3 0
'9= ;- o
-
9
s i: .
!
€
_
E
Y
r|1
a
i
9
tr_
X : ' ag + I
r E Z {e :
;
a
H H ' : ! a ' : : X F
= ; J . Y Z Y U 5 0
6 v
o
E
e : t € F 3
a
o
3
5,;
d e E
4'43
d a u
E;'E
=v ( t vr
F^
4
,t-
f iS E t € € : E
z
a
boo o
6
O
c-;i
:.):
5 e e
a t Y
> - d ;
r
!
Ec g 9o
I
o-tr
,:
119
120
Chapter 5
5.8
Soil Comqaction
Determination of Field Unit Weight of Compaction
When the compaction work is progressingin the field, knowing whether the specified
unit weight has been achievedis useful. The standard proceduresfor determining
the field unit weight of compaction include
l. Srnd conc mcthoL
2 . R u b b e r b a l l o o nm e t h o d
3. Nuclear method
Following is a bricf description of each of thesemethods.
Sand Cone Method (ASTM Designation D-I556)
The sand conc device consistsof a glassor plasticjar with a metal cone attached at
i t s t o p ( F i g u r c - 5 . 1 7 )T. h c i a r i s f i l l e d w i t h u n i f o r m d r y O t t a w a s a n d .T h e c o m b i n e d
w c i g h t o l ' t h c i a r . t h c c o n e ,a n d t h e s a n df i l l i n g t h e j a r i s d e t e r m i n e d( W ' ) . l n t h e f i e l d ,
1 small holc is excavatedin the area where the soil has been compacted.lf the weight
o1'themoist soil excavatedfnrm the hole (Wr) ir determined and the moisture contcnt of thc cxcavatcdsoil is known. the dry wcight of thc soil can be obtained as
W3l +
whcrc tr,
W.
u)e/")
l(x)
n t o i s t u tc c ( ) t t l c n t .
Figure 5. 17 Glass jar filled with Ottawa sand with sand cone attached
(s.11)
5.8 Determination of Fietd IJnit Weight of Compaction
I,
'.,
'
.lar
*/'
Ottawa sand
..'
\
vill\c
C,rnc *
t'"t
.,i..........
Mctrl
plrrle
'/
\
Hut" fiiled with
C)ttawasand
(a)
(b)
Figure 5. 18 Field unit weight determined by sand cone method:
(a) schematiccliagram;
(b) a test in progress in the field
Chapter 5 Soil ComPaction
After excavation of the hole, the cone with the sand-filled jar attached to it is
inverted and placed over the hole (Figure 5.18).Sand is allowed to flow out of the jar
to fill the hole and the cone. After that, the combined weight of the jar, the cone, and
the remaining sand in the jar is determined (lVa)' so
( s.12)
Ws: Wt - Wq
where W, : weight of sand to fill the hole and cone.
The volume of the excavatedhole can then be determined as
tv/
-
W.' - W,.
(s.13)
-
7ri(sand)
where I42.: weight of sand to fill the cone only
: dry unit weight of Ottawa sand used
7ri(sancl)
are determined from the calibration done in the laboThe values of I4z,and 7,1(sanct)
ratory. The dry unit weight of compaction made in the field can then be determined
as follows:
Dry weight of the soil excavatedfrom the hole
f,t
Rubber Balloon Method
w1
(-s.14)
Volume of the hole
(ASTM Designation
D-2167)
The procedure for the rubber balloon method is similar to that for the sand cone
metltod; a test hole is made and the moist weight of soil removed from the hole and
its moisture content are determined.However, the volume of the hole is determined
by introducing into it a rubber balloon filled with water from a calibrated vessel,
fiom which the volume can be read clirectly.The dry unit weight of thc compacted
soil can be determined by using Eq. (5.1a).Figure 5.19showsa calibratedvessclthat
would be used with a rubber balloon.
Nuclear Method
Nuclear density meters are often used for determining the compacted dry unit
weight of soil. The density meters operate either in drilled holes or from the ground
ruriu.". The instrument measuresthe weight of wet soil per unit volume and the
weight of water present in a unit volume of soil. The dry unit weight of compacted
soilian be determined by subtracting the weight of water from the moist unit weight
of soil. Figure 5.20 shows a photograph of a nuclear density meter.
Figure 5.19
Calibrated vesselused with rubber
balloon (not shown) (courtesyof
John Hester, Carterville, Itlinois)
Figure 5.20
Nucleardensitymeter (courtesyof
David A. Carroll, Austin, Texas)
123
124
Chapter 5
Soil ComPaction
table:
Laboratorycompactiontestresultsfor a clayeysilt aregivenin the following
Moisture
content(%)
Dry unit weight
{kN/m3)
14.80
1.7.45
18.52
18.9
18.5
t6.9
b
8
o
1l
t2
1"4
performedon
Followingare the resultsof a field unit weight determinationtest
the samesoil by meansof the sand-conemethod:
. Calibrateddry densityof Ottawasand : 1570kg/m3
r Calibratedmassof Ottawasandto filIthe cone : 0'545kg
o Massof jar + cone* sand(beforeuse): 7.59kg
r Massof jar + cone + sand(after use) : 4'78kg
. Massof moist soil from hole = 3.007kg
r Moisture contentof moist soil : 10'2%
Determine
a. Dry unit weightof compactionin the field
b. RelativecomPactionin the field
Solution
a. In the field,
:
:
Massof sandusedto fill the hole and cone 7.59kg 4.78kg 2'81kg
=
Massof sandusedto fill the hole : 2'81kg 0'545kg 2'265kg
2.265kg
Volume of the hole(Y) :
of Ottawa sand
density
Dry
kg
.2'265 - = 0.0014426
m3
1570kg/m'
Moist densityof comPactedsoil :
Massof moist soil
Volume of hole
ke/ml
? 92''^.: 2084.4
Moist unit weight of compactedsoil
0.0014426 j
(2084.4)(e.81
) :
2O.45kN/m3
1000
Hence,
v
td
^1 +
w (o/"\
100
2A.45 :
18.56kN/m3
t0.z
1+."--_
100
5.9 Compaction of Organic Soil and Waste Materials
125
z
>
*'
('/c)
Figure 5.21 Plot of laboratorycompactiontestresults
b. The results of the laboratory compaction test are plotted in Figure 5.21.
: 19 kN/m3. Thus, from Eq. (5.6),
From the plot, we see that 7rl(max)
_ - 7,rrri"r.r) 18.56 -:
97'70/"
lg"o
,rr""
5.9
Compaction of Organic Soil and Waste Materials
The presenceof organic matcrials in a soil reducesits strength. In many cascs,soils
with it high organic content are gcnerally discardedas fill material; however,in certain economic circumstanccs,slightly organic soils are uscclfor compaction. In fact,
organic soils are desirablein many circumstances(e.g.,fbr agriculture,decertificat i o n , m i t i g a t i o n ,a n d u r b a n p l a n n i n g ) .M o r e r c c e n t l y ,t h e h i g h c o s t so f w a s t ed i s p g s a l
have sparked an intercst in the possibleuse of waste materials (e.g.,bottom ash obtained from coal burning, copper slag,paper mill sludge.shreddedwastetires mixed
with inorganic soil, and so forth) in various landfill operations.Such use of wastematerials is one of the major thrusts of prescnt-dayenvironmcntal geotechnology.Following is a discussionof thc compaction characteristicsof somc of these materials.
Organic Soil
Franklin. Orozco, and Scmrau (1973) conductedseverallaboratory teststo observe
the effect of organic content on the compactioncharacteristicsof soil. In the test program, various natural soils and soil mixtures were tested.Figure 5.22 shows the effect of organic content on the maximum dry unit weight. When the organic content
exceeds8 to 10%, the maximum dry unit weight of compaction decreasesrapidly.
Conversely, the optimum moisture content for a given compactive effort increases
with an increasein organic content. This trend is shown in Figure 5.23.Likewise, the
maximum unconfined compressionstrength (see Chapter l0) obtained from a compacted soil (with a given compactive effort) decreaseswith increasing organic content of a soil. From thesefacts,we can seethat soilswith organiccontentshigher than
about 10% are undesirable for compaction work.
126
Soil Compaction
Chapter 5
105
to
100
l5
o
o\'
,?
z
qn
t l
E
il
Oven-dried
c
x
t
.:
E
Air-dried --
t l
€
!
tr
= R o
'i
=
E
n >
o Mixture-oven-dried
. Nalurrl silmple oven-dried
a Mixture-air-dried
l t
t0.22
0
5
1
0
1
5
2
0
Organiccontent(o/o)
2
5
3
0
Figure 5.22 Yariation of maximum dry unit weight with organic content (after Franklin,
Orozco, and Semrau, 1973)
^ 3 0
t
o
t<
o
'6
E r o
'a
o t 5
-l 0" 0
5
20
15
l0
Organiccontent(70)
25
Figure 5.23 Yariatton of optimum moisture content with organic content (after Franklin,
Orozco, and Semrau, 1973)
5.9 Compactionof OrganicSoitand WasteMaterials
127
Soiland Organic Materiat Mixtures
Lancasteret al. (1996)conductedseveralmodified Proctor
teststo determinethe
effect of organiccontent on the maximum dry unit weight
urrJ opti-u- moisture
contentof soil and organicmaterialmixtures.The soils
iested.onrirt"d of a poorly
gradedsandy soil (Sp-SM)mixed with either shredded
redwoodbark, shredded
rice hulls,or municipalsewagesludge.Figures5.24
and5.25showthe variationsof
O Redwoodbark
1 R i c eh u l l s
O Sludge
z
-
11
.:l
I
lll
':
!
r
l.
8
.E
u
20
10
60
80
t(x)
Organic content (o/o)
Figure 5.24 Yariatictn .f maximum^dry unit weight
of compaction with organic content _
soil and organic material mixtures. st,Lirce:Aftei"The gffect
of organic clontent on Soil
compaction." by J. Lancaster, R. waco. J. Towre,
and R. chane y, tioo. rn proceedings,
7'hird Internationar syrnposium on Environmentar
Geotechnrroly, p. tsv. used with permis_
sion of the author.
1t
s'-
11
c
o
a
=
'I
)t I
rr
t r '
6
'E
rU
l+
I2
Organic
content
(7o)
Figure 5'25 Yatiation of optimum moisture content
with organic content - soil and organic
material mixtures. Source: After "The Effect of
organic content on Soil compaction,,, by
J' Lancaster, R' waco, J' Towre, and R. chaney, 1sg6. proceedings,
tn
iii)a nternatronat
Symposium on Environmentar Geotechnology,p.
159. Used with pJrmission of the author.
128
Chapter 5 Soil ComPaction
maximum dry unit weight of compaction and optimum moisture content, respectively, with organic content. As in Figure 5.22, Ihe maximum dry unit weight decreascdwith organic content in all cases(seeFigure 5.24).Conversely,the optimum
moisture content incrcasedwith organic content for soil mixed with shredded redwooclor rice hulls (seeFigure 5.2-5),similar to the pattern shown in Figure 5.23.However, for soil anclmunicipal sewurgcsludge mixtures, the optimum moisture content
remained practically constant (sec Figure 5.25).
Paper Mill Sludge
Paper mill sludge.despite a high watcr content and low sttlid contents,can be compactecland uscd for landfill. The statcsof Wisconsin and Massachuscttshave both
u s c c lp a p e r m i l l s l u c l g ct o c a p l a n d { i l l s .M o o - Y o u n g a n d Z i m m i e ( 1 9 9 6 ) p r o v i d e d
thc standarclProctor compaction charactcristicsfor severalpaper mill sludges,and
t h c s c a r e s h o w n i n F i g u r c . 5 . 2 6T. h c p h y s i c a lp r o p c r t i e so l ' t h e s es l u d g e sa r e s h o w n
in Tlblc -s..1
Bottom
Ash from Coal Burning and Copper SIag
Labgratory standard Proctor tcst rcsults for bottont ash f'ront coal-burning power
plants ancl I'rtrcopper slag arc also availablc in thc litcraturc. These waste products
as lantllill. A summary of some
have bccr-rshown to bc cnvironnrcntallysal'cl'or r-rse
'l'able
-5.4.
ol'thcsc tcst rcsults is giver.rin
r
a
o
o
S l u t l g cA
S l u t l g c1 3
S l u t l g cl )
Sludgc I.i
z
!
/
c
c
a
0
-50
"'utn,r,u,.'lln,"n,
,'r"lt"'
2s0
300
Figure 5.26 Yariatt<tnof dry unit weight of compaction with moisture content for paper mill
sludge. Source: From "Geotechnical Properties of Paper Mill Sludgesfor Use in Landfill
Covers," by H. K. Moo-Young, T. F. Zimmie, 7996,Journal o.f Geotechnical Engineering, 122
(9),p.768-775. Copyright O 1996American Societyof Civil Engineers.Used by permission.
5.10 Special Compaction Techniques
129
Table 5.3 Physical properties of SlurJgesShown
in Figure 5.26
A
B
D
E
Moisture
content (%)
Organic
content (%l
-25i)
1.50
200-250
l -50-200
I -50-200
4-5-50
-56
41
35-44
Specific gravity
of solids, G,
I.88-1.96
l.f.i3-l.u5
r.93-1.9-5
1.962.08
Plasticity
index
191
1.5
lt7.-5
proctorTestResultsof Bottom
Table
5'4 standarcr
Ash ancrcioppcrSrag
Maximum
dry unit
weight
tb /ft3
Bottom ashbituminouscoal
(WestVirginia)
Bottom ash lignitecoal
Copperslag
5.10
Fort Martin
Kamntcr
K a n a w h aR i v c r
Mirchcll
Muskingham
Willow Island
[3ig Stonc Powcr
P l a n t ,S o u t h D a k o t a
Anrcr-icanSmclter ancl
Rclincry Clompany,
Ill Paso,Jtxas
Optimum
moisture
content
(%l
I3.4
16.0
I 1.4
I IJ.3
14.3
14..5
16.4
8-s
t02
72.6
l 16.6
9 l. l
L)2.4
104..1
24.5
13.t3
26.2
14.6
22.0
2 1. 2
20.5
19.8
t26
l8.ri
S c a l s .M o u l t o n , a n d R u t h
(1e72)
Das. Selinr. and pl'cifle
( I e78)
D a s , ' l h r q u i n ,a n d J o n c s
( ler]3)
Special Compaction Techn iques
Severalspccial types of compaction techniques
have becn dcvcropeclr.orcleepcom_
pactiol"tof in-placc soils, ancl these techniques
are used in the fietd fbr large-scale
compaction works. Among_these,the popurar
methods are vibroflotation, jynamic
and brasring.Derairs of the.scmethods are provi<lcd
in the foirowing
::L:i::tr"'
Vibroflotation
vibroflotation is a technique for in situ d,ensification
of thick layersof loose granular soil deposits.It was devcloped in Germany
in the 1930s.The first vibroffotation
device was used in the United Statesabout l0years
later. rn.fro..r,'
involves the
use of a vibroflot 5.27 (arso cailed the vibrating
unit), whichis about 2.1 m (:7 tt)
long' (asshown in Figure 5.27.)This vibrating
unit has an eccentricweight inside it
and can develop a centrifugal force, which enibles
the vibrating urit to vibrate horizontally. There are openings at the bottom and
top of the vib'iating unit for water
jets' The vibrating unit is attached
to a folrow-up pipe.Figure 5.27 showsthe entire
assembly of equipment necessaryfor conducting
the field"compaction.
130
Chapter 5
Soil Compaction
fir.,
,ffi#fu
ee*scr*;--Follow-up
-.
j
;
"
i
C y l i n d c ro l c o r n p a c t c d
nrateriirl,addedl'rom the
s u r l a c et o c o m p e n s a t c
lirr the loss of volume
causedhy the increascol'
d e n s i t yo f t h e c o m p a c t e d
soil
B
C y l i n d c ro f c o m p a c t e d
nraterial,producedby a
s i n g l ev i b r o f l o tc o m p a c t i o n
Figure 5.27 Yibrofrotationunit (after Brown, 1977)
The entire vibroflotation compaction process in the field can be divided i
four stages(Figure 5.28):
The jet at the bottom of the Vibroflot is turned on and lowered i
the ground.
Stage2: The water jet creates a quick condition in the soil and it allows the
brating unit to sink into the ground.
Stage3: Granular material is poured from the top of the hole. The water from
the lower jet is transferred to the jet at the top of the vibrating unit.
This water carries the sranular material down the hole.
Stagel:
5.10 Special Compaction Techniques
131
S t a g c3
Figure 5'28 Compaction hy vibroflotation proccss(alter
flrown. 1977)
Table5.5 Types of Vibroflot Units'.
75 kW electric
and hydraulic
Motor type
23 kW electric
a, Vibrating tip
Length
Diameter
Weight
Maximummovemcnt when full
Centlifugal force
2 . 1m ( 7 . 0I ' t )
z 1 0m
6 n r( 1 6i n . )
r 7 . 8k N ( 4 ( X nl b
))
1 2 . -m
5 m ( 0 . 4 9i n )
1 6 0k N ( l t 3t o n )
l.fi6m(6.llf'r)
3ttl rnnr( 1.5in)
l7.lJkN (4(XX)
ltr)
7 . 6m m ( { ) . 3i n . )
l J gk N ( 1 0t o n )
1 . 2k N ( 2 6 0t b )
3lJmnr ( l.-5in)
6 1 0m m ( 2 4i n )
1800rpm
0 . 7 6k N ( 1 7 0 l b )
3 2 m m ( 1 . 2 5i n )
3 t Xm
) m ( 1 5 . 2 -i n
5. )
Itt00rpnr
0 - 1 . 6m r / m i n( 0 - 4 ( n g a l / m i n )
7 0 0 - 1 0 - 5k0N / m , ( 1 0 0 _ 1 . 5l b0/ i n 2 )
0 - 0 . 6 m r / n i n ( 0 - 1 5 0g a l / m i n )
7 0 0 - 1 0 - 5k0N / m r( 1 0 0 l 5 0 t b / i n r )
b. Eccentric:
Weight
Offset
Length
Speed
c. Pump
Operatingflow rate
Pressure
d. Lower follow-up pipe und extensions
Diameter
305mm (12 in.)
Weight
3.6-5
kN/m (2,50
lb/ft)
*AfterBrown (1977.)
3 0 5m m ( 1 2i n . )
3.6.5
kN/m (2s0lb/fr)
Stage4: The vibrating unit is gradually raised in about
0.3 m (:l ft) lifts and
held vibrating for about 30 secondsat eachlift. This process
compacts
the soil to the desiredunit weight.
The details of various types of Vibroflot units used
in the United States are
given in Table 5.5. Note that 23 kw (30-hp) electric
units have been used since the
latter part of the 1940s.The 75 kw (100-hp) units were
introduced in the earlv 1g70s.
132
Chapter 5
Soil Compaction
\
/
fl::,:l';,H:".."
Figure 5.29 Probcspacingfor vibroflotation
The zone of compaction around a singleprobe varieswith the type of Vibroflot
useil.the cylindrical zone of compactionhas a radius of about 2m (:6 ft) for a 23 kW
(30-hp) unir. This radius can exrcnd ro about 3 m (: l0 ft) for a 75 kw (100-hp) unit.
Compaction by vibroflotation is done in various probe spacings,dependingon
the zone of compaction. This spacingis shown in Figure 5.29.The capacity for successluldcnsification ctl'irt situsoil dependson severalfactors,the most important of
which is the grain-sizeclistributionof the soil and the type of backfill used to fill the
holes during the withdrawal period of the Vibroflot. The rangc of the grain-sizedistribution of in situsoil marked Zonc I in Figure 5.30is most suitable1'orcompaction
by vibroflotation. Soils that contain excessiveamounts of finc sand and silt-sizeparticles arc difticult to compact,and considcrableeffort is necded to rcach the proper
relative density of compactictn.Zone 2 in Figure -5.30is thc approximate lowcr limit
of grain-sizedistribution for which compaction by vibroflotation is effective.Soil deposits whose grain-sizedistributions fall in Zone 3 contain appreciableamounts of
gravel.For these soils.the rate of probe penctration may be slow and may prove une c o n o m i c a il n t h e l o n g r u n .
n ystern
U n i f l e dS o i l C l a s s i l i c a t i o S
Grain size (mm)
Figure
5.30 Effective range of grain-size distribution
of soil for vibroflotation
5.10 Special Compaction Techniq
{35
(Y)
The grain-sizedistribution of the backfiil material is an imoorran
controls the rate of densification.Brown (Igjll has defined a quantit
suitability number for rating backfill as
- i 3
r,ry:LV1r;
*
|
*
6
1
orrt,
(-5.1s)
where Dsc,,D.u, and D',, are the diameters (in mm) through which. respectivery,50,
20, and 10./" of the material Dasses.
T h e s m a l l e rt h c v a l u e . , t S r . t h " m o r e d e s i r a b l et h e b a c k f i l lm a t e r i a l .F o l l o w ing is a backfill rating systemproposed by Brown:
Range of S,
0-10
I0-20
20-30
30-.s0
>-50
Rating as backfill
E,xcellcnt
Good
Fair
Poor
L]nsuitablc
Dynamic Compaction
D y n a m i c c o m p a c t i o ni s a t e c h n i q u ct h a t h a sg a i n e dp o p u l a r i t yi n t h e U n i t c c lS t a l e s
for the densificationof granular soil deposits.This proccssconsistsprimarily of dropping a heavy weight repeatedlyon thc ground at regular intervals.The weight of the
h a m m e r u s e d v a r i e so v e r a r a n g e o f 8 0 t o 3 6 0 k N ( 1 l Jt o g 0 k i p ) , a n d t h e h e i g h t o f
the hammcr drop varies betwcen 7.-5ancl 30.-5m (2.,5and 100 ft). The stresswaves
generated by the hammer drops aid in the dcnsification.The desree of compaction
a c h i e v e da t a g i v e ns i t e d e p e n d so n t h c l b l l o w i n g l h r e e l a c t o r s :
1. Weightof hammer
2. Height of hammer drop
3. Spacingof locations at which the hammer is dropped
Leonards, cutrer, and Holtz (19u0) suggestedthat the significant depth of
influencefor compaction can be approximated by using the equation
D:(lSlw,n
(,5.t6)
where D : significantdepth of densification(m)
W11: dropping weight (metric ton)
/.t : height of drop (m)
In English units, the preceding equation takes the form
D: 0 . 6 1 v w
where the units of D and h are fr, and the unit of I4zais kip.
( s.17)
134
Chapter 5
Soil Compaction
Blasting
Blasting is a technique that has been used successfullyin many projects (Mitchell,
1970)for the densificationof granular soils.The general soil grain sizessuitable for
compaction by blasting are the same as those for compaction by vibroflotation. The
process involves the detonation of explosive charges such as 60% dynamite at a
certain depth below the ground surfacein saturatedsoil. The latcral spacingof the
chargesvariesfrom about 3 to 10 m (10 to 30 ft). Thrce to five successfuldetonations
are usuallynecessaryto achievethe desiredcompaction.Compaction up to a relative
density of:rbout 80% and up to a depth of about 20 m (60 ft) over a large arca can
easily be achievedby using this process.Usually,the explosivechargesare placed at
a clepthof about two-thirds of the thicknessof the soil layer desiredto be compacted.
Exa mp l e5 .4
Followingare the detailsfor the backfillmaterialusedin a vibroflotationproject:
' D n : 0 . 3 6m m
t Dzl'= 0'52mm
. D s o: 1 . 4 2 m m
Determine the suitability number S". What would be its rating as a backfill
material?
Solution
From Eq. (5.15),
SN
-* 1 1
m
' ' ' V|
-- t' 1'\
*
(4,,)t
r - - - j - + - .
(Dri'
(D,,,)'
m
l
(t.442 (0.s2)'z (0.36)'z
= 6.1
Ratins: Excellent
Example5.5
For a dynamiccompactiontest we are giventhe followi -ng:weight of hammer :
15 metric tons and height of drop : 12 m' Determine t$ significantdepth D of
;
influencefor compaction,in meters.
Solution
From Eq. (5.16),
D : G){wrt: (l){rsXra : 6.71m
Problems
5.11
135
Summary and GeneralComments
Laboratory standard and modified Proctor compaction tests described in this chapter are essentially for impact or dynamic compaction of soil; however, in the laboratory, static compaction and kneading compaction can also be used. It is important
to
realize that the compaction of clayey soils achieved by rollers in the field is
essentially the kneading type. The relationshipsof dry unit weight (7,1)and moisture
con_
tent (rv) obtained by dynamic and kneading compaction ur. noi the same. proctor
compaction test resultsobtained in the laboratory are used primarily to determine
whether the roller compaction in the field is sufficient.The siructuresof compacted
cohesivesoil at a similar dry unit weight obtained by dynamic and kneading .o-_
paction may be different. This dift'erence,in turn, affectsphysicalproperties
such as
hydraulic conductivity,compressibility,and strength.
For most fill operations,the final selectionof the borrow site dependson such
factors as the soil type and the cost of excavationand haulins.
Fill materials for compaction are generally brought to the site by trucks and
wagons.The fill material may be end-dumped,side-tlumped,or bottsm-4umpetl
atthe
site in piles. If the material is too wet, it may be cut and turned to aerate and dry before being spread in lifts for compaction.If it is too dry, the clesiredamount of
water
is added by sprinkling irrigation.
Prohlems
5.1
5.2
5.3
5.4
Given G, : 2.72,calculatethe zero-air-voidunit weight for a soil in lb/ft3 at
w : 5"/" , 8y", 10"/", 12"/", and 15% .
Repeat Problem 5.1 with G" : 2.62.plot a graph of
7,nn*(kN/m3) againstw.
calculate the variation of dry unir weighr (kN/m3) of i ioil
1c. : i.es1 at
w : 10"/" and 20"/" for degree of saturation (S) : g0% 90yo, and 100"/o.
,
The resultsof a standard proctor test are given below. Determine the maximum dry unit weight of compaction and the optimum moisture content.
Vorume
or
T?:::frt
Proctormold
(ft3)
in the mold
flb)
content
(/"1
3.26
8.4
10.2
l/30
U30
l/30
t/30
t/30
5.5
5.6
4.l-)
4.67
4.02
-r.o-t
Moisture
1L-,)
14.6
16.8
For the soil describedin Problem 5.4, if G" :2.72, determine the void ratio
and the degree of saturation at optimum moisture content.
The results of a standard Proctor test are given in the following table. Determine the maximum dry unit weight of compaction and the optimum mois-
Chapter 5
Soil Compaction
ture content. Also. determine the moisture content required to achieve95%
of 7a(-o*).
Massof
Volume of
Proctormold
(cm3)
943.3
943.3
943.3
943.3
943.3
943.3
943.3
943.3
5.7
5.9
wet soil
in the mold
(kS)
1.68
1.71
1.7'7
1.83
1.86
t.[3tt
1.87
1.t35
Moisture
content
t%l
9.9
10.6
t2.1
t 3.[t
l -5.1
17.4
19.4
21.2
A field unit weight detcrmination test for the soil describedin Problem 5.6
vielded the following datzr:moisture content : 10.27"and moist unit
weight : 16.1kN/ml. Determine the relative compaction'
The in sl/& moisture content of a soil is 18% and the moist unit weight is
105 fb/ft3.The specihcgravity of soil solids is2.15.This soil is to be excavated
ancltransported to a constructionsite for use in a compactedfill. If the specificzrtionscall for the soil to be compactedto a minimum dry unit weight of
lb/ftr at thc samc moisture content of 18%, how many c-ubicyards of
103.-5
soil from the excavationsitc are nceded to produce 10,000yd' of compacted
fill? How many 20-ton truckloads are nceded to transport the excavatedsoil?
A proposed embankment fill requires 5000 m3 of compactedsoil. The void
ratio of the compactedllll is specifiedas 0.7. Four borrow pits are available
as dcscribed in the following tablc, which lists the respectivevoid ratios of
the soil and the cost pcr cubic meter for moving the soil to the proposed construction site. Make the necessarycalculationsto selectthe pit from which
thc soil should be bought to minimize the cost. Assume G. to be the same at
all pits.
Borrowpit
Void ratio
Cost{$/m3}
A
B
C
D
0.u5
1.2
0.95
0.75
9
6
7
l0
5.10 The maximum and minimum dry unit weightsof a sand were determined in
the laboratory to be 104 lb/fc and 93 lb/ft3, respectively.what would be the
relative compaction in the field if the relative density is 78Y"?
5.11 The maximum and minimum dry unit weights of a sand were determined in
the laboratory to be 16.5 kN/m3 and 14.6 kN/m3, respectively.In the field, if
the relative density of compaction of the same sand is7O"/",what are its relative compaction (%) and dry unit weight (kN/m3)?
References
197
5'12 The relative compaction of a sand in the
field is 94o/o.Themaximum ancl
minimum dry unit weights of the sand are 103lb/ft3
and ss tblrc, ."rp".tively.For the field condition, determine
a. Dry unit weight
b. Relative density of compaction
c. Moist unit weight at a moisture content of
l0%
5.13 Laboratory compaction test resultson
a crayeysilt are given in the fblrowing
table:
Moisture
content (%)
6
u
9
ll
t2
t4
Dry unit
weight (kN/m3)
r4.80
t7.45
1u..52
I u.9
I fi.6
16.9
Following arc the resurtsof a field unit weight
determination test on the
s a m es o i l w i t h t h e s a n dc o n e m c t h o d :
. C a l i b r a t e dd r y d c n s i r y
o l O t t a w a s a n d : 1 6 6 7k g / m 3
o calibrated mass.,f ottawa
sanclto fill the cone : 0. l r 7 kg
. Mass of jar * cone + sand (before
use) : 5.99 kg
. M a s so f j a r * c o n e + s a n d
( a l t e r u s e ) - 2 . t i 1k g
. Mass of moist soil from
hole : 3.33I ks
. M o i s l u r cc o n t c n to l m o i s t
soil _ | I.by,
Determine
a. Dry unit weight of compaction in the fielcl
b. Relative compaction in the field
5.14 The backfill matcrial fbr a vibrollotation project
has the following grain
sizes:
. D r , , : 0 . 1 Im m
. D z , t : 0 .l 9 m m
. D s , : 1 . 3m m
Determine the suitability number, S1u,
for each
5.15 Repeat Prcblem -5.14using the followins
values:
D , , , : 0 . 0 9m m
D1, : 0.25 mm
D 1 , : 0 . 6I m m
References
Av'r<rcaN Assocranr.rN op Srane Hrcrrwev aNo
TRaNspoR.rATroN
o.pr.raLs (1gg2).
AASHTO Materials,part II, Washington.D.C.
AveRrceN S.cre'v poR TesrrNcro"o irot..nrnr-s (1999).
ASTM standards,vor 04.0g,
pa.
WestConshohocken.
138
Chapter 5
Soil ComPaction
BRowN, E. (19'7'7)."Vibroflotation Compaction of Cohesionless Soils," Journal of the Geotechnical Engineering Division, ASCE, Vol. 103, No. GT12' 1437-\457'
D'AppoloNra, D. J., WHrrnaRN,R. V., and D'AppoloNte, E. D. (1969)."Sand Compaction
with Vibratory Rollers," Journal of the Soil Mechanics and Foundations Division,
ASCE, Vol.95, No. SMl,263-284.
A. A., and Pnelnl-r, T. W. (1978). "Effective Use of Bottom Ash as a GeDa.s, B. M., Sgr-rr,,r,
otechnical Material," Proceedings,5th Annual UMR-DNR Conference and Exposition
on Energy, University of Missouri, Rolla' 342-348'
Dns. B. M., Tenerrrr, A. J., and.IoNes. A. D. (1983)."Geotechnical Propertiesof a Copper
Slag," Trunsportation ResearchRecord No. 941, National Research Council, Washington, D.C., l-,1.
Fn,rNrr-rN. A. F., Orrozco. L. F., and Snunau, R. ( 1973)."Compaction of Slightly Organic
t oJ the SoitMechanicsand Fountlatkns Division, ASCE, Vol.99, No. SM7'
Soils,"Jorrrna
541-5-57.
H<'tut7..R.D., and K6vRcs, W. D. (1981).An IntroductioLtto GeotechnicalEngineering,Pren'
tice-Hall, Englewood Cliffs, N.J.
JogNsctN.A. W., and Snr-LeERc,J. R. (1960)."Factors That lnfluence Field Compaction of
Soil." Highway ResearchBoard. Bulletin No- 272.
LnHreE. T. W. ( 1958)."The Structure of Compacted Clay," .lournal of the Soil Mechanics and
FoundatiotrsDivisiort,ASCE, Vrl. lJ4,No. SM2, l6-54-1 to 1654-34'
LnN<.as.r'nn,J., Wac.o, R., Towlu, J.. and cHnNev, R. (1996)."The Effect of organic con3rd lnternational Symposiumon Environmcntent on Soil Compaction," Proceeding.s,
tal Geotechnology,San Diego, 152-161'
LpE. K. W., an6 SrNc;lt,A. (1971). "Relative Density and Rclativc Compaction," Journal of
the soil Mechanicsand FoundutionsDivision, ASCE, Vol.97, No. SM7, 1049-1052.
p.
Ler,.. y.. and SrrEornvp, R. J. (1972)."Characteristicsof Irregularly Shaped Compaction
curves 6f Soils," Highway ResearchReatrd No.38l, National Academy of Sciences,
Washington,D.C., l-9.
LpcrNa.nos,G. A., Cr;.r-rER,W. A., anrJ Hots'2, R. D. (1980). "Dynamic compaction of
Granular Soils," ,/gurnal of the Geotechnical Eng,ineering,Division, ASCE, Vol. 106'
No. GTl.35-44.
Mrr.c.rrEr.r.J. K. (1970). "ln-Place Treatmcnt of Foundation Soils," Journul of the Soil Mechunicsantl FoundutionsDivision, ASCE, Vol. 96' No. SMI ' 73-110'
Moa;-YogNc;, H. K.. and ZIMMIE, T. F. (1996). "Geotechnical Properties of Paper Mill
Sludges for Use in Landfill Covers," Journal of Geotechnical Eng,ineering,ASCE, Vol.
1 2 2 ,N o . 9 , 7 6 8 - 7 ' 7 5 .
pnocrcrn, R. R. ( 1933)."Design and Constructionof Rolled Earth Dams," EngineeringNews
Recor d. Y ol. 3, 245 -248, 286-289, 348-35 1, 372 -31 6.
SEnrs. R. K. MoUu|oN, L. K., and Ru rs, E . (19'72)."Bottom Ash: An Engineering Material," Journal of the Soil Mechanics and Founrlations Division, ASCE, Vol. 98, No. SM4'
311-325.
SEep, H. B. (1964).Lecture Notes, CE 271, Seepageand Earth Dam Design, University of
California, BerkeleY.
U.S. DepanrMENT oF Nevv (1971). "Design Manual-Soil Mechanics,Foundations, and
Structures."NAVFAC DM-7,U.5. Government Printing Office, Washington,D.C'