Directions for obtaining soil samples

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Directions for obtaining soil samples

CAN AD) Ser T H l 392 no. 10 c . a Em.

DIRECTIONS

FOR

O B T A I N I N G SOIL SAMPLES h ' s l i e C, Wilson A b s t r a c t

-

D i r e c t i o n s a r e g i v e n f o r so51 sampling pru- cedwes t h a t c a n be done by any p r a c t i c a l

person w i t h o u t s p e c i a l i z e d trafnfng* Instruc- tlon p r o c e d u r e s f o r d i f f e r e n t types of samples,

i

,e, disturbed and undisturbed, are o u t l i n e d ,

including samples a b t a l n e d from b o r S.ngs and test p d t s a s well. a s t h e equipment necessary f o r eacli job, Suggested references

an

the sub-

j e c t a r e a l s o given.

77y3i'rG L-'-

VlSlON OF BUlLalNG R E S E k R C H

-

N A T I O N A L RESEARCH C O l J N C l l O T T A W A , C A N A D A

DIRECTIONS

FOR

OBTAINING SOIL SAEPLES by

L e s l i e C, IVilson

T h e h s t i n g a f soils i s now a standard p a r t o f the a p p r o v e d procedure in designing foundations of s t r u c t u r e s , or in _analyzing

Faundatlon difficulties which have a r i s e n , Such soil t e s t s can

o n l y be a s good a s t h e samples on which they a r e p e r f o r m e d , and the t a k i n g of s o i l s a m p l e s i s t h e r e f o r e a n i m p o r t a n t part o f e a c h

sf these procedure s o

Soil sampling for engineering p w p o s e s is o f t e n considered t o b a m a t t e r r e q u i r i n g highly t r a i n e d personnal, c o s t l y boring equipment, and s p e c i a l s a m p l e r s of intricate d e s i g n . While this i s of'3en t r ~ e , good quality sampling may a l s o be done by t h o s e

without s p e c i z l training w l t h equipment which can be Improvised f o r t h e p u p a s e a Patience and c a r e f u l workmanship a r e t h e main essentials,

The decision a s to when and where so51 sampling s h o u l d be done w i l l depend on a number of f a c t o r s which cannot b e discussed in thls Nothe

It

is i m p o r t a n t , however, t h a t soil sampling, when done, s h o u l d be to a m i n t m u a n d e p t h o f s e v e r a l f e e t below f o u n d a t t o n l e v e l , a n d p r e f e r a b l y to s o l i d rock, b s t i m p o r t a n t of all, to be

o f any r e a l v a l u e , the samples t a k e n s h o u l d be t r u l y representa- t l v e of t h a s o i l b e i n g sampled,

So51 samples a r e u s u a l l y c l a s s i f ' i e d a s e i t h e r n d i s t u r b e d i f or Hundi s t ~ w b e d ' ~ ,

For many p u r p o s e s s u c h a s identification of so31 sype and

c l a s s i f i c a t i o n t e s t s , I'di stuFbedw samples w i l l suffice. In t h e s e samples t h e structure of the soil is disturbed but a l l the ori- ginal s o i l constituents a r e still In t h e i ~ o r i g i n a l p r o p o r t i o n s ,

On

o t h e r o c c a s i o n s "undisturbedfT samples may be r e q u i r e d .

These a r e samples 3n which the s o i l has undergone s o little disturbance t h a t t h e y a r e s u i t a b l e f o r laboratory t e s t s to

d e t e r m i n e physical properties such a s s h e a r s t r e n g t h , and

oon-

s o l i d a t i o n characterSstics of the soTlo The term "undisturbedn lmplies t h a t the disturba.nce has been reduced to a n u n a v o i d a b l e minimum, although some d i s t w b a n e e of the s t r u c t u r e O f the soil

i s i n e v i t a b l e through trlmming t h e s u r f a c e of the sample, and a l s o through'removal of the weight of the o v e r l y i n g soil.

The moat satisfactory method of o b t a i n i n g e i t h e r t y p e of sample f s very o f t e n by means of a t e s t pit, Unless s p e c i a l

boring equipment and s k 2 l l e d personnel a r e available, undis- t u r b e d sa'mples c a n only be o b t a i n e d f r o m open e x c a v a t i o n s , As

t e s t p l t s can be r a t h e r c o s t l y , e s p e c i a l l y ir depths a r e great or f f g~oundwater conditions are d i f f f c u l t , a more economical method sf e x p l o r a t i o n I s by means of b o r i n g s , These can be

made by several m e t h o d s according to the equipment available and the r e s u l t s r e q u i r e d , Only the simplest methods w i l l be con-

s i d e r e d h e r e ,

V a r i o u a klnds of augers m a y be used f o r soil borfngs whfch allow d i s t w b e d samples of soil 'to be r e c o v e r s d , Augers

s u i t a b l e f o r soil sampling a r e commercially a v a i l a b l e , and if much b o r i n g is to be done, it will p r o b a b l y be found advisable to puschase a s u f t a b l e a u g e r s e t , including extension r o d s , choppfng bits, and o t h e ~ attachments,

An o r d l n a r g post-hole a u g e r t s qu9te s u i t a b l e f o r s h a l l o w

depths, however, and most models can be extended for moderate depths, using s t a n d a r d p i p e a n d c o u p l i n g s ,

A carpentergs auger of about 1 112-inch d i a m e t e r welded to

a l e n g t h of

3/8-inch

p i p e makes a u s e f u l s o l 1 a u g e r o E x t a n s l o n rods and a T-handle o m a l s o be made f r o m s t a n d a r d pipe and

fittingsd

The boring procedure 1 s t o advance the a u g e r a f e w inches

a t a t i m e and w i t h d ~ a w 9t, examining the soil b r o u m t up,

If

She s o i l f s emptled

from

_{t h e a u g e r in successfve p i l e s}

_fn

brderly ~ o w s , a s t u d y of the full s o i l p r o f i l e Ts made e a s i e r

and d d v i d i n g p o i n t s between s t r a t a can be seen more ~ e a d i l y , Soil f ~ o m the s i d e s o r the h o l e m a y stick to the soil on the

a u g e r a s it 5 s befng w Z t h d ~ a w n f r o m the h o l e , so t h a t care is sometimes r e q u i r e d to e d e n t i f g it c o ~ r e c t l y a If d e s i r e d ,

however, fairly good r e p r e s e n t a t i v e sasnpfes can be obtained

w i t h

t h e

auger, although the rno5sture c o n t e n t of the s o L l may

Sample s should be t a k e n f r o m each aoiZ layes., and a t

r e g u l a r intervals of dep$h

in

a p p a r e n t l y uniform soil. Samples

t a k e n f r o m the auger should be a e a l e d in s m a l l glass jars or -

o t h e r air-tigh%'eontafners to guard agafns$ l o s s of r n a l s t u r e ,

,and c l e a r l y l a b e l l e d for shippfng t o the l a b o r a t o r y f o r

testingo SSnee the moisture content of s o i l fs a very impor-

t a n t property, it is essential that a s lfttle as possible of the natural moisture c o n t e n t be a l l o w e d to e v a p o ~ a t e , ThPs w f l P

s t a r t a s soon a s a sample is exposed the aPr,

It

I s of the greatest importance, t h e r e f o r e ,

( a ) t h a t soil samples be p l a c e d in their

con-

t a i n e r s immed9ately a f t e ~ t h e y a r e ob- t a i n e d from the ground;

( b ) that the c o n t a i n e r s be f i l l e d w l t h the sample, 1 leaving little or

no

a i r

space

Into

which moisture can evaporate; and

( o ) t h a t the contafner-s be s e a l e d t t g h t l y a s

soon 'as the samples ape fn them, s e a l e d

p ~ e f ' e r a b l y with p a ~ a f f i n waxa

A r e c o ~ d should be kept of the date of boring, method o f boring, l o c a t i o n of b o r e h o l e , e l e v a t i o n of ground s u r f a c e , depth of a l L samples, thickness and a s h o r t d e s ~ r f p t i o n of e a c h layer

o$' s o i l encountered, d e p t h a t

which

groundwater is encountered and some indication of the r a t e of f l o w ff possible, and any athey points of significance,

It

may occasionally be necessaFy

to the hole, p a z ~ t i c u l a r l y nearp

%he

surfam, te support

the s i d e s , Thts can be done wibh p i p e h a ~ i n g an inside dfameter slightly l a r g e r than t h e diametez. of the augero The depth t o which auger b o ~ b g s can be c a r r f e d depends l a r g e l y on the

n a t u r e of the-soil and the equipmen5 used, b u t depths o f 25 Seek

should u s u a l 1 be possible wtthout t o o much difffculty, Depths of more than

g

O P e e t have been successfully e x p l o r e d

En

t h % s way,

A word of cautSon should be said abouta a l e s s s a t i s f a c t o ~ y method af

so51

exploration hewn a s wash b o r f n g ,

In

t h i s method

a p i p e is inserted fnto t h e g ~ o u n d w h j t l e water is pwnped through

it. Various kinds of b t t s are dssd on the e n d , ' o f the pipe to

Loosen the sol1 and the p i e c e s of s o i l a r e c a r r i e d up and away

with

the wash watero By watching t h e wash w a t e ~ , one can g e t some in-

d i c s r t f o n of the type of soiL being passed through, and when

changes

Tn

s t r a t a a r e r e a c h e d , Considemble s e g r e g a t f on of s o i l g r a i n s of various s i z e s t a k e s p l a c e , however, and owfng to the mfxlng t h a t f n e v l t a b l y o c c w s , strata s e v e r a l f e e t thfck can

eaa5lg be overlooked, For this Peason samples o f s o i l taken f i o m the wash water

are

a o m p l e t e l y un~&liable and should n e v e r be used, Vkshfng l a oftera of value, however, a s e, means of advancing a

P r o b i n g with a long rod Ss s o m e t L m e s of value

in

d e t i r - mini& the d e p t h o f a soft surface l a y e r , but this method

i s

not u s u a l l y v e r y r e l i a b l e ,

T e s t

Pits

The s l z e of the excavation for a test p F t and the need for

bracing will depend on l o c a l c o n d i t i o n s , A record of the s o l 1 p r e f l l e should be kept, a s d e s c r i b e d in the section

on

S o i l Borings. R e p r e s e n t a t i v e samples may be takgn a s ~ e q u i r e d f r o m f r e s h l y e x c a v a t e d s e c t i o n s of the p i t before t h e so51 h a s had

t i m e t o dry out on e x p o s u r e to the a f r ,

In

many instances test pits p r o v i d e the most r e l i a b l e

method o f s o i l sampling, since a f u l l and a c c w a t e examination

of soil conditions in place can be made. The c o s t i s highel.

than b o r b i g s , however, and the depth i s more ILmfted, Good- qua15 t y u n d i s t w b e d sampling

in

bore hole s requires s p e c i a l sampling equipment and advanced technf ques, and even t h e n f s

not a l w a y s satisfactory,

Undisturbed S a m p l h g

In

Open Pits

The s i m p l e s t t y p e o f u n d i s t t m b e d sample is o b t a i n e d by

c u t t i n g a chunk of s o i l o u t o f an open p i t and cover9ng it to p r e v e n t breakage a n d moisture change, This method can o n l y be

u s e d with s o i l s that will not b r e a k o r crumble w h e n being re- moved, D h t a l l e d inst~uctions f o r th5s procedure f o l l o w ,

[ a ) q u i p m e n t

Spade, butcher knife, t r o w e l , spoon, hacksaw b l a d e s ,

p a r a f f i n , s t o v e , can

in

w M c h to h e a t p a r a f f i n , paint brush, c h e e s e c l o t h (or twine, friction t a p e or waxed p a p e r ) ,

(b) To obta5n chunk sample from bottom of p i t

1,

Excavate test pit

In

such a manner t h a t y o u do n o t stand d i r e c t l y above sample while at Least t h e l a s t

9

f n c h e s of s o i l are removed f r o m above the sample;

2 0 Carefully smooth the g ~ o u n d s u r f a c e and mark o u t l i n e of chunk, A p p r o x i m a t e l y a 10-tnch cube of s o i l f s n a ~ m a l ly re qulred;

3 0

Excavate t ~ e n c h a r o u n d chunk ( ~ i g ,

4.

Deepen e x c a v a t i o n and t r i m s i d e s of chunk with b u t c h e r knife, Mark a "T~' on t o p of chunk;

5 .

Cut

off chunk with b u t c h e ~ k n i f e , t r o w e l ,

or

hacksaw blade

I F ~ E ,

l b ) a n d c a r e f ~ l l v r e m n w m frnm h n l ~ -

( c )

TO

o b t a i n chunk sample f r o m v e r t i c a l f a c e of plt 1, C a r e r u l l y smooth the v e r t i c a l surface, cuttPng

back 2 o~ 3 lnehes f r o m original s i d e of p i t , and mark o u t l f n a of chunk;

2, Excavate carefully around and behfnd chunk,

Shape chunk r o u g h l y wlth b u t c h e ~ knife ( F S ~ , 2), &irk

" ~ ' b n

t o p o f chunk;

3.

C u t o f f chunk a n d c a r e f u l l y remove from hole,

If

a number of sarn l e s are to be c u t , it may be found con- v e n i e n t to make up a " c L! ay k n i f e w , Thf s c o n s i s t s of a s t e e l

s t r i p a t t a c h e d to a wooden h a n d l e , as shown fn Fig,

3 ,

A w i r e saw, a l s o shown, i s usefulo Wsfng t h & s a tools,, the tfme and work in removing chunk samples may be c o n a i d e r a b l g reduceda

The p r o c a d w e I n t a k i n g a sample f r o m a v e r t i c a l f a c e 'is to cut gpooves about

3

inches wide into the face a t the t o p and t w o

s i d e s o f t h e b l o c k , and then to cut dawn t h e back and out th$ bottom w i t h t h e wire saw,

If

the sample s t i l l adheres t o o

s t r o n g l y

fn

s p i t e of t h e w i r e saw c u t , a pfeee of s h e e t metal

may be pushed u n d e ~ I t to f a c i l i t a t e I t s removalo (d)

To

seal chunk

-

The sample should be sealed a f t e r removal f r o m

the pito

l o T r E m and shape r o u g h edges with butcher knLfe

Mark t o p and botkcm w i t h l e t t e r s "TTr and "Btf s c ~ a t c h s d

on

soil; 2, Apply three c o a t s of paraffin w i t h b r u s h *

P a r a f f f n should ract be h o t t e r than necessary to m e l t it, A l l o w

e a c h c o a t to coo: a n d became f i r m b e f o ~ e applySng

next

c o a t ; 3 Wrap wlth cheeseclath or o t h e r s o r t loth ha

If

cloth is not a v a i l a b l e , r e i n f o m e w i t h s e v e r a l l o o p s of frfction tape or twine, Waxed paper can also be u s e d as a substltuta f o p c h e e s e c l o t h , but does not glve a s much strength, Apply three

more c o a t s of p a r a l f f n ,

T h e

t o t a l khfckneas of p a r a f f i n shauld be a t l e a s t

118

f n e h o A l a b e l f d e n t P f y 5 n g t h e s a m p l e and

markfng the t o p and bottom s h o u l d be s e t

on

the sample and painted over with the last l a y e r or two of the p a r a f f i n *

( e

b

To obtaln sarn~nes in a c o n t a i n e r

WSth s o i l s which do not c o n t a i n s t o n e s of any

a p p r e c i a b l e s i z e , or whfch are not s t r o n g enough to allow c u t t i n g of a chunk sample a a descxdjbed above, a "cylfnder'' or ''box

1 a Use a l a r g e fmhf t c a n , the t o p of which h a s

been cleanly removed, Punch

one

or two s m a l l a 9 r h o l e s

in

_{t h e}

battonr. of the can;

2, T r i m a chunk of soil to be a little l a r g e r than t h e i n s i d e of the can;

3 .

Place the c a n on t o p o f t h e chunk, then

slowly and g e n t l y push it .down over the soil, w h i l e t r i m P n g

the sample to t h e correct size ahead of it (Fign

4)

e If s t o n e s

i n t e r f e ~ e , pfck them o u t carefully and backfill with s o i l ,

noting this in the l a g of sample;

4.

When t h e can is f u l l , c u t the sample f r e e well

b e l o w the b o t t o m edge, us4ng a 3pade;

5-

Invert the can a n d t r i m the top o f the sample

ta a b o u t 112 Snch below t h e t o p of the can;

b o

Pour h o t p a r d f i n i n t o any crsvlcss between ehs

sample and contaTner and over the t o p and bottom of the c y l f n d a r ,

Use s e v e r a l layers of cheesecloth and paraffin to s e a l t h e can

and p r e v e n t m o i s t m a loss or movement of t h e sample,

A small wooden box may be used a s a c o n t a f n e r I n s t e a d of a

can,

In

thf s case t h e top and b o t t o m of the box should be

removed before p l a c i n g it over the ~ a m p 1 . e ~ Before the sampla

5 s c u t f r e e , i t s

t o p

s h o u l d be trTmmed, marked wfth a "T"

c o a t e d with p a r a f f i n , and the t o p of the box replaced.

&en

t h e

box i s i n v e r t e d , the other end i s marked with a " B ' b a n d t r e a t e d

sTrnilarlg, Screws should b e u s e d to attach the top and bottom of the box to a v o l d j a r r i n g the sample when the box i s assembled and d l s m a n t l e d ,

E a c h sample s h o u l d be l a b e l l e d clearly w i t h t h e name of the p r o j e c t , bore hole or test pPt number and location, sample

number, d e p t h of sample, and, in the c a s e of undisturbed samples,

"

t o p and "bottomn,

Undisturbed samples should be packed w i t h a t l e a s t 2 or

3

inches a f metst sawdust all a r o u n d , and e n c l o s e d in a s t r o n g

wooden b o x o Disturbed s a m p l e s should be packed in a c a n t a l n e r

strong enough to prevent. damage, Samples should be protected

A d d i t f onal fnfomnatfon w h f c h should accompany samples depends

oe

I n d i v i d u a l cfrcumstances, but in g e n e r a l should

inc lude :

1,

Site

p l a n o f p r o j e c t , indicating positions of b o r e holes and t e s t p b t s ;

2, Note

on

groundwater conditions and d i r e c t i o n of local drainage;

3 -

Note on weather conditions p r i o r to sampling which might cause unusual moisture c o n d i t i o n s ,

For further Information on s o i l sampling, the reader is

referred to the follclwing publications, f r o m which much o f the m a t e r i a l

In

this Note has been adapted:

Hvorslev, M, Juul, ' q S u b s ~ r f a c e Exploration and Sampling or S o l l a f o r C i v i l Engineering Purpose s n ,

W a t e ~ w a g s Experimene s t a t i o n , V i c k s b w g , Miss,

This

book i s a v a i l a b l e f r o m The Engineerln Foundatton,

2 9

W,

39th

S t r e e t , N e w York

18,

Y b P r i c e i s $

J?

.00 to members of the founder s o c i e t i e s , $6,00 to non-members, !Phis

is an excellent and comprehensive r e f e r e n c e covering all phases of* t he subject

In

considerable d e t a i l o

B e r t r a m , Major George Eo, ''Soil T e s t s f o r Military

Construction", Technical B u l l e t i n No. 107,

1946,

ArnerZcan Road Buildersy Associa t l o n ,

1319

F, S t r e e t

Northwest, Washington

4,

D O C ,

Describes soil samplfng and t e s t l n g methods simply

and c l e a r l y u Cone ludin-B

I$

is hopad t h a t t h e directions g i v e n

in

t h i s Note w i l l be of h e l p to those w h o w i s h t o o b t a S n soil samples, It as

necessary t h a t p e a t care be t a k e n

in

the p r o c u r i n g and s t o r a g e

treatment o f such samples, The l a t t e r i s n e c e a s a r g in o r d e r to prese=.ve, a s w e l l a s possible, the d i f f e r e n t p r o p e r t i e s of the

s o l a

Xn

each sample The m o s t important yule

In

any sampling

proesdme i s t o make stare t h a t t h e sample taken is ~ e p r e s e n t a t i v e

cf t h e s o i l b e i n g sampled a s no l a b o r a t o r y t e s t I s b e t t e r than

I,

(a) P R E P A R I N G S A M P L E

FIG. 2 C H U N K S A M P L E F R O M V E R T I C A L S U R F A C E

(b)

C U T T I N G S A M P L E

F I G . 3 W I R E S A W A N D C L A Y K N I F E

T R I M D O W N b O U