Compaction of soils for fills and embankments

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CANAD S er TKL B92 no. 1 3 d . 2 -.

COMPACTION

OF

SOILS FOR

_a-

iQ4L

y ~ - ~ > . >

--%a

FILLS

Am

E3,faANKMENTS

w4;g'

'2,Rb Robert F, Legget -- ! E, ,_I I .-

i

Z

1

DEC

The information

in

this Mote is based

an

an

article by the a u t h o r which appeared in t h e October

1944

i s s u e of " ~ o a d s and B r i d g e s " .

-? -- ,,?

: .

; C)' -%.-?

Gompactlon of Sofls f o r

FSLla

and

f i b ankment s

by R o b e r t F. Legget

T h e c o n s t ~ u c t i o n of embankments and rflls is

probably one of the o l d e s t o f a o n s t r u e t i o n o p e r a t i o n s .

Indeed, t h e r e are in exf stence e a r t h embankments

(fn

C e y l o n , f o r example) which are known to be at l e a s t f o u r

thol~send y e a r s old and which a r e stfll

In

good condition and

in

s e r v i c a ,

The methods of constructfng embankments changed v e r y I r t t l e mtEl the fntrsductlon of modern mechanical

e qszlpment. A f t e r such equfplnent came I n t o general. use the

c o n s t r ~ c i c f o n o f e v b a n h e n t s became more rapld and more economical, b u t even then t b b s s S s of the methods used

remained t h e same, UntS1 r e l a t i v e l y s e c e n t l y , embankments have been c o n s t r u e t e d by e f t h e y end-tfppfng or s f d e - t f p p i n g

soil o u t of t h e v a r f o u s t y p e s of e a r t h - c a r r y f n g equfplnent

and allowfng it t o come to r e s t at i t s n a t u r a l s l o p e .

Not all embankvents e o n s t m e Q e d

fn

this way have

been suceessf

ul.

L i t t l e , howevers has been pub11 shed about

the f a t l u r e s of" t h e s m a l l t y p e s of embankments encountered

In

o r d f n a r y hfghway w o ~ k , a l t h o u g h t h e r e are available

r e c o r d s of many f a i l u r e s of Zarsger embankments such as those f orrnfng e a ~ t h dams, F a f l u m s have taken the form of' s e r f ous s l f p p a g e s and e x c e s s t v e settlements and these f e a t u ~ e s are

not uneamon fn the c a s e of yoadway embankments and o~dfnary

f f 11s.

New

S o l 1 S t u d i e s _--v

Since the m a k e r l a 1 fn nse is

4 0 f 1 ~

ft I s

not

surprfslng t h a t the development of the new study of safl

mechanics has l a d to changes

fn

the method af forming

embankments, w l t h consequent Improvemen* 9n the art. As is

g e n e ~ a l l y known, no e a r t h dam of any appreaf able size would

t o d a y be oonstrucr;ed w i t h o u t the a l d of' the techniques made

avafla'ole by s t u d i e s %n soil mechanics, On the o t h e r hand, t h e same technfques have n o t y e t

cone

i n t o general use Sn

Canada for the canztruetfon of smaller embankments and F k l l s

s u c h as are f r e q u e n t l y a f'ea'twe of heghway work.

It

is the

purpose of thla Note to s u g g e s t how these modem teehnf s u e s

can be applied to o r d i n a r y rill c o n s t i r u c t i o n and t o i l l u s t r a t e t h e i r a p p l f e ~ t f o n by reference t o some examples f r o m p r a c t f c e ,

Fundarrisntals of Embankment C o n s t r u c t i o n

What are the

f

mdarnent a1 s of eqbankrnent cons tructiont'

S t a b P l f t y of the foundatton material i s t h e F f r s t e s s e n t i d ;

e q u a l l y i m p o r t a n t is the ~ ~ t a b i l i t y

or

the embaikment s t m e t u r e Itself d u ~ i n g and a f t e r constructfon. S t a b f l f t y of' the

embankment implfes t h e r e t e n t f on of ft D shtxpe, a m i n e m u m of

s e t t l e m e n t a n d , I n some c a s e s , r e a s o n a b l e f m p e r m e a b f l i t y

.

A

third and f f n a l requirement is t h a t methods of construction s h o u l d be ~ l a t f v e l y sEmpla and economical fn cost,

S t a b S l S t y of the fomdatSion beds of embankments can

r e a d a l y be e n s u r e d by the c a r r y f n g - o u t of adequate s u b s u r f ace e x p l o r a t S o n in a d v m c e of' eonstruction, There are now

a v a f l a b l e s i v p l e slzd economfcal methods f o r carrglng o u t s u c k f n v e s t 2 g a t I c n s . Subsof ls should always be I n v e s t f gated So a

d e p t h at; l e a s t twfce t h e w l d t h of the embankment, srfice to

t h f s d e p t h the graulnd b e n e a t h an ernbanknent is always s t r e s s e d

to an a p p r e c i a b l e degree b y t h e wefght of the fill. If the

r e s u l t s o f the t e s t b o r f n g s and test pits a m p r o p e r l y h t e r p r e t e d

and supplemented when necessary by s o l 1 t e s t s , there should be

no reason why the fozlndatf o n b e d s of embankments should n o t

p e r f o ~ n s a t i s f a c t o r f l y and as ant!tcfpated, S t a b i l i t y of F P l l a

The s t a b 5 1 S t y of embankment structures depends upon the mechanical p r o p e r t f e s of the sox1 of which they a r e built.

It

I s f o r thfs reascn t h a t t h e r e s u l t s of s t u d f e s In soil mechanics c a n be so u s e f u l l y a p p l i e d to t h e f r analysfs,

If

sand i s to b e used as the fill material, few problems are

i n v o l v e d , provfded t h a t t h e sand c a n be placed in a t h o r o u g h l y compacted @anditLon,

If, on

the a t h e r hand, pure c l a y I s the p r o s p e c t i v e m a t e r l a l f o r the embankment, It w f l l u s u a l l y be

g o o d p a l i c y to seek f o r o t h e r s o i l s m o r e s u f t a b l e

far

t h e p u r p o s e , For the g r e a t majority of ordienary embankments and

rills,

the

s o l l s avaflable

Ife fn

between these t w o extremes,

being c l a s s f r i e d as safl m.fxtures.

It

f a in t h e age of such

s o l 1 m?txtures f o r embankment .work t h a t p e a l progress can be made by the a d s p t f o n or modern techniques and c o n t r o l methods,

One

of the Sfrst p u b l i c a t i o n s to s u g g e s t the methods

now in use w a s a paper on a r o c k - f l l l dam

in

Australla p u b l f s h e d

in the Proceedings of t h e Institution of C i v i l Englneers for

the y e a r 193Sp by A . A a Kelso, sn A u s t r a l f a n engineer,

On

this continent it w a s the p u b l i e a t f o n by R, R , P ~ o c t o r in Engfneerfng

News-Record of his f amotrs s e r f e s of f o u r art1 c l e s on the

compact%on of e a r t h f f l l s whfch d i r e c t e d g e n e r a l a t t e n t i o n to

thFs m a t tsr. ( "Fundamental P r Z n c l p l e s o f S o i l C o m p a c ~ f an,

"

The testz

now

befcg u s e d

Pn

connectfon wL:n

e m b a n h s n t s t a b i l i t y we b ~ s e d on P r o c t o r " work

an3

are

c o n ~ a n l ; ~ c a l l e d b y his name. The essence of P r a c t o ~ s s

s u g g s s t i o n s can be A l l u s t r a t e d by

a

s3ropPe graph such as t h a t in tha a c c ~ m p a n q b g f i g u r e ,

If

a s o i l mixture is

c,onrpactsd in a c o n t a i n e r of known v01um under s t a n d a ~ d

c o n d i t f o n s , a csr3eeln slue w f l l be obtaened f o r I t s

d e n s i t y (usaa19g s t a t e d as t h e cEry weight per cubfc. f o o t ) .

If t c t h f s soil w a t e ? be added m d t h o r o u g h l y mixed, and

the r e z ~ ~ l t f n g ; cc<% m i x t w a agafiz be compacted in t h e same con%aincr under the same condftfons, t h s d r y density w i l l

be fou-rld to h a ~ e incrsssed, This p m c e s s c a n be cant9nued ( a s 3h:m on the C ~j m L f l V ~ a c e ~ t a i n op.e;imum mcrlstupe

e o n t e n t 1 s ~ e a c h ~ d , a f t e r whfeh the b y d e n s f t y w f l L

decrease with She addftZon cf' m m e v a t e ~ , P r s r c t u s z x p l a l n a thlls r e s u l t by suggeskfng t h a t the water p r e s e n t tends So lubrfeetze thq p a r t % c l e a of soil, w h i ~ k z a r e t h e r e f o r e f o ~ c e d

c l o s e r %oge'thsrll t h u s g f ~ l n g a more c o n p a c k mass so T o n g as

t h e r e are any v o i d s l e f t

Yn

$ha soil mfxture, Once 8 i E l She

vo%ds ars f i l l e d , the a d d f t l o n of more water w'L2.P merely

tend t o s e p a r a t e the s o f l p a r t f c l e a , t h u s r e d u c i n g %be

effective d r y wefghk, T h e f u l l e x p l a n a t i ~ n is

m o m

zomplfca-

t e d thm- t h l s , being a s s o c i a t e d w i t h the p ~ o p e ~ t l e a of

mofsture f i l m s on the so51 particles, b u t Prc-ctomhPa e x p l a n a t i o n

fs one easSZy undersk006, and is esaentfally sound,

The p r a c t i c a l h1p9icatfons are f r n p o r t a n t ,

If

a

s o l 1 be laced 9n p c s i t i o n under t h e eondftf ons noted by t h e

77 I ?

pofnt A oa the c u r v e , T t can be aornpacted tat0 a hard dense mass, b u t ft s t 2 1 conta'ins a considerable voPxam.4 of v o i d s

which will be occupied by water if w a t e r comes in s o n t a e f

w f t h t h e embankment ef t h e y as pain or in any o t h e r way,

In

t h e example, t h e moisture c o n t e n t c a n be i n c ~ e a s e d f r o m E3. pel.

cent t o 13 p e r c e n t x i t h o u t eny ehmge Sn the volume

of

the

soil* A l t h o u g h f i m when oonk&fnfng-only 9 per cent, the sfill

may a n d p ~ c b a b l y wS13 b e q u t t e w e t and ''s7,op~y'' when c o n t a f n 5 q

13 p e r cent of water, 1% 13 f o r thfs reason that sc mmy

embankments have f afled

in

t h e p a s t , d e s p 9 t e the f a c t thaQ when p l a c e d t h e y appeared t o be firm a n d s o l i d , Ff, on th+e o t h e r hmd, t h e sofl is p l a c e d

En

p o s i t i o n a% OF, a b o u t the

o p t l m u n ~ o i s t u r e c o n t e n t m d eornpac ted, 4ct

will

b e ssen % h a t

no more w a t e r can e n t e r fntc the s a i l , sfnea p r a c t i c a l l y a13 the o r i g i n a l v e l d s are a l r e a d y r f l l e d w f t h the smaller a ~ i l p m t f c l e s

m e

the character of the s o l 1 w - k l l bYherefa~e no5 change w i t h the passage of t f m e -

The essence, t h e r e f m e , sf t h e modern mp,thcd cf placing s o l l s f n embankments 1s to p l a c e them In posikfun at

or about t h e optfmum .xzisfsture content and t ~ j compact thsm b y s u i l t a b l e m a n s so aa to gst t h e m a x ! ~ u m densfty practicable,

There are a v a f l a b l a s t a n d a r d spe@lffcatfons::- gfvfng 6 e t a f l s

-

--

-

s;: See Standard S p e c S T i a a t i o n s f o r Highway N a t e r i z l s and

Methods of Sampling and Testing, Am, A s s o e , S t a t e Higkrway

Offfcfals, 1942 edition, Method

T99-38;

a n d alsc A , S , T , E , T e n t at1 ve S t a n d a r d Dh9R-11 ?T ( .TIIT w 7 n C n 1

of +,he s o - c a l l e d P r o c t o ~ t e s t f a r determining the a p t l m m

moisture

c o n t e n t

and density, a t e s t which r e q u l r e s a

m l n l m u r n o f simple e q u i p m e n t and which 19 r e l a t f v e l y e a s y t o c a r r y out,

Construct1

on

P r o c e d u r e

In

actual constructTon p r a c t f ce, d t e r a soil has

b e e n s e l e c t e d foa use in an embankment, l a b o r a t o r y tests have first to be c o n d u c t e d

In o r d e r

t o d e t e m f n e the optlrnm m o i s t u r e c o n t e n t f o r the 3091 and the aax4mum practicable

density. When these v a l u e s a r e a v a i l a b l e p l a n s c a n be made

for p l a c i n g the sofl I n positfon under the d e s t ~ e d condft2ons. This u s u a l l y means addlng w a t e r to t h e s o i l e f t h e r

Sn

the

b o r r o w p f t or a f t e r 5t has been p l a c e d , by m e a n s of a w a t e r -

tdistriblating t r u c k , or in som o t h e r s u f t a b l e way, placing

the sofl

in

posftion

in

t h i n l a y e r s ( u s u a l l y f r o m

6

to 9 in',

I n thf ckness) and compacting these l a y e r s by s h e p s f k o t r o l l e r s ,

multiple-kfred r o l l e r s

or

three-wheeled r o l l e r s . D u r l n g the constructt;fon o p e r a t f o r , the molstare content of the compacted

m a t e r i a l must be p e r i a d i c a l l y checked and its compacted

d e n s i t y determined, Thf s c a l l s f ' o ~ the s e r v l c e of Inspectors

who have b e e n t r a i n e d to conduct the necessary efrnpPe check t e s t s and also t h e p r o v i s i o n of a small but slmple f i e l d

l a b o r a t o r y .

The

f o r e g e l n g d e s c r i p t f o n p e sents only the e saent;ial f e a t u r e s of modern embankment c o n s t r u c t l o n . Those I n t e r e s t e d c a n o b t a i n f u l l e r p a r t f e u l a r s

in

the several, publleations

on

t h e s u b j e c t

now

a v a i l a b l e . There w f l l be some who have n o t

seen these methods

In

o p e r a t f o n e n d who may c o n t ~ a s t t h e

processes d e s c r i b e d w i t h t h e m o r e u s u a l s t r a l g h t f c l ~ w a r d tEppfng

of soil into desf-red posltfon I n an embankmwnk, They may c o n s l d e r t h a t the c o m p a r ~ s o n a e r e l y aham the addltfon o f

complf c a t 1 ons to

an

otherwf se straightforward o p e r a t l o n , There may b e o t h e r s who w f l l classify t h e suggested method aa y e t

another Inemsf on of academf c rnfnds i n t o the f P e l d of c o n s t ~ u c - t f on.

It

m a y be noted that t h e main part of the Shand

D m on

the

Grand River in southwestern O n t a r f o , containing almost one

m i l l i o n clzbfc yards of fflls was completely c o n s t r u c t e d o v e r

a decade ago b y u t i l i z f n g the methods d e s c r t b e d , Other srnallsr darns and fflls I n t h e w e s t o f Canada have been s i m f l a ~ l y

c o n s t r u c t e d .

In

the United S t a t e s t h e r e are now innumerable

examples which can be q u o t e d ta illustrate t h e p ~ a c t f

cal

a p p l i c a t i o n of the m e t h o d s described, A m a j o r i t y of t h e

l e a d i n g state hfghway departments have now adopted the m e t h o d s

d e s c r i b e d as t h e i r standard p r a c t i c e , so t h a t t h e y have long ceased t o b e "academfc",

F u l l - S c d a Researches

One of the

must

u s e f u l d e s c r l p t % o n s o r the use of these vethods is c o n t a i n e d

in

an a r t l c l e

en

the

o f r i e i a f

j o u r n a l of' the U , S , P u b l i c Roads Adm-lnfstr?atfon, P u b l f c Roads ( July-August-Septembe~r I s s u e ,

1944,

Val.

24,

pages 1 to 2 6 ) - This p a p e r by Eenry Aman, W,

T,

Spencer and H, E, Marshall

g i v e s a s u m w y of t w o f u l l - s c a l e yesearch p r o j e c t s carr4ed

out f n c o n j u n c t f o n w l t h the U . S . P u b l i c Roads A d m i n i s t r a t f o n

In the s t a t e s of Indf ana and Ohio,

It

Sa of some I n t e r e s t to n o t e that the t e s t s were

not c a r r l e d o u t to check the v a l f d i t y of the method, sfnce

it

i s stated t h a t " g r e a t e r s t a b l t l i t y of f i l l s has been obteined

w h e r e v e r t h i s t e s t has been a d ~ p t e d as a b a s 5 s f o r c o n t r o l l f n g

compaction"'. Rather, t h e p r o j e c t s =re c w r i e d o u t t o o b t a i n answers to e e r t a f n d ~ t a f l e d questions regarding the applfcation

o f the m e t h o d descr5bed, such as "the e f f i c f s n c y of' d i f f e r e n t t y p e s of r o l l e r s I n o b t a i n b g the d e s i r e d r e s u l t s , the r e l a t i o n

of t h e d e p t h of l a y e r t o t y p e of r o l l e r , the aconamfcs and

1imit;ationa of m o i s t u r e c o n t r o l , and t h e performance o f t h e

completed fill w S t h r e s p e c t to settlement and change in

s t a b i l L t y f f

.

The projects were c a r r f e d out on embankments farm%-ng

part o f the hfgbway systema of t h e two states,

In

el%,

seventeen s e p a r a t e s e c tf o n s were cons t r u c ted-eeight in Indf ana

varying

in

l e n g t h rrom 400 to 500 f t. and B i n e in Ohio varyfng I n l e n g t h Prom 400 to 700 ft, The t e s t s e c k f o n s bad a t o p

w l d t h o f

42

ft. a n d s i d e s l o p e s of 2 to 1 on the Indiana

p r o j e c t and 1-112 to 1 on the Ohfo p r o j e c t . T h e heights v a r S e d

up to

₂₁

f t o , so t h a t the e m b a n h e a t s were by no m e a n s e x p e r f - mental

tn size.

The soils ranged

f m m

stlty c l a y learns t o

almost puPe c l a y s , Three t y p e s of m l l e r s were used--sheepsf o o t , threemWheel and pneumatf e - t b e d r o l l e ~ p of d f f ferent capacrf t 9 e s.

The paper g l v e s unusually f u l l d e t a i l s of t h e r e s u l t s o b t a i n e d and is w e l l w o r t h y of s t u d y b y all i n t e r e s t e d

fn

embankment c a n s t ~ u c t f i o n , While

no

unit c o s t s a r e gSven, r a t e s

of p r o g r e s s are clearly s e t out f ~ r a r n which m l t c o s t s can be

c a l c u l a t e d b y those i n t e r e s t e d , The c o n c l u s i o n s a r r i v e d a t by

c o n s i d e r a t i o n of b o t h s e r i e s of t e s t s a m presented 5n d e t a f l

for the two p r o j e c t s s e p a r a t e l y , T h e more i m p o r t a n t flndings may be summarized as f o l l o w s :

(I)

"The compaction test may 'be u t i l i z e d g e n e r a l l y to c o n t r o l t h e construction of em3ankment;a regardless of the type of

compacting equipment. It o f f e r s a p r a c t f c a l m e a n s of determ5nfng when a Layer of 3011 fs s a t f s f a c t o r i l y compacted. 'l

12) S o i l s sirnilas t e those .cornprls3ng t h e f i l l s on t h e s e p r o j e c t s mag be r e a d i l y compacted to the d e s i r e d d e n s i t y by

any of t h e rollers u s e d If the moisture content of

the

so77

( 3 )

The mofsture content sf

r i l l s

c a n be c o n t r o l l e d w i t h i n

3

per c e n t of the optfmum v a l u e when

the

s o l l I s a b t g l n e d f r o m a borrow p i t , b u t such r%g3d

field

c o n t r o l does n o t seem

j u s t i f f e d In the light of the r e s u l t s sobtafned,

(4)

A d e n s i t y e q u a l to

95

p e r c e n t of t h e maxf?ium o b t a f n e d

Sn

compaction t e s t s f s a p p a r e n t l y satiaZactory when the t y p e s of soils and the d e p t h of' the f i l l s a r e similar to those of

the p r o j e c t s d e s c r i b e d and when t h e r n o i s t u r e c a n t e n t s a r e T e a s o n a b l y c l o s e t o t h e optlmum.

( 5 )

h he compaction of areas r o l l e d at maxlrnurn r o l l e r speed

is e q u a l to t h a t o b t a l n e d at s l o w e r speeds. The higher speed8 r e s u l t k t a corresponding increase in r o l l e r capacity,'

( 6 )

S e t t l e m e n t s , which were c a p e f u l l y o b s e r v e d a f t e r

construction, were e x t r e m e l y small, averaging

U,OS

f t o for the

Indlma p r o j e c t and 0.025 f t. Zor the Oh50 p r o j e c t ,

In

view

of thls

It

is s t a t e d t h a t "such embankments may be paved

immediately rollowing constructEorl w i t h o u t d a n g e r of detrfrnen-

tal settlementn.

(7)

"The constructfen of embankments may be c o n t r o l l e d fn

accordance wf t h the moisture contents and densf t i e s Sndf c a t e d

by compaction test data w T t h o u t causfng delay In constructfon

o p e r a t i o n s . "

When it I s r e c a l l e d t h a t these conclusions a r e based

on f u l l - s c a l e c o n s t ~ ; l c t i o n o p e r a t i o n s c a r r i e d out B y two

l e a d i n g s t a t e hieghway dep-trnents, t h e f r s 5 g n i f i c a n c e w f l l be apparent, The l a s t conclusion s h o u l d s e t a t rest the d o u b t s

which r o a d b u i l d f n g cont~actors may p o s s i b l y e n t e r t a i n w h e n i n t r o d u c e d to the m e t h o d s .

If

f u r t h e r e v l d e n c e as t o the p r a c t i c a b i l f t y of

u t i l f zing the technique d e s c r i b e d f o r plactng embankments is

neezed, reference need o n l y be made to the l n d i v f d u a l p r a c t i c e s

of a l a r g e number of t h e o t h e r s t a t e hfghway departments of

the United S t a t e s , The s t a n d a r d p r a c t l c e of many of t h e s e

departments may perhapa be c k l a ~ a ~ t e ~ 1 z e d b y the f o l l o w h g

statement r e g a r d i n g t h e p r a c t i c e

in

CalWornXa nade a l i t t l e t f m e

err

by T. E, S t m t o n (of the C a l i f o s n i a State Hlghwag Department): "Standard C a l i f o r n i a p r a c t f c e r e q u f r e s that

embankments be c o n s t r u c t e d and ceasol5dated

In

l a y e r s n o t

nore than 8

En,

t h f c k b e f o r e compaction and t h a t each l a y e r

b e consolidated by r o l l i n g to a r e l a t i v e compactlon or n o t l e s s than 90 p s r cent b e f o r e s u b s e q u e n t l a y e r s are p l a c e d .

By thls m e t h o d , combined wfth r i g i d c o n t r o l o v e r t h e n o i s t u r e

content, i t has been found posslble to construct embankments