Sensitivity in leda clay

Publisher’s version / Version de l'éditeur:

Nature, 197, 4865, pp. 347-348, 1963-04-01

READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE. https://nrc-publications.canada.ca/eng/copyright

Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.

Questions? Contact the NRC Publications Archive team at

PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information.

NRC Publications Archive

Archives des publications du CNRC

This publication could be one of several versions: author’s original, accepted manuscript or the publisher’s version. / La version de cette publication peut être l’une des suivantes : la version prépublication de l’auteur, la version acceptée du manuscrit ou la version de l’éditeur.

Access and use of this website and the material on it are subject to the Terms and Conditions set forth at

Sensitivity in leda clay

Penner, E.

https://publications-cnrc.canada.ca/fra/droits

L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.

NRC Publications Record / Notice d'Archives des publications de CNRC:

https://nrc-publications.canada.ca/eng/view/object/?id=8849554b-4af1-43b3-b611-2384c8f8774a

https://publications-cnrc.canada.ca/fra/voir/objet/?id=8849554b-4af1-43b3-b611-2384c8f8774a

S e r

TH1

N2lr 2

no.

181

c . 2

NATIONAL

RESEARCH

COUNCIL

CANADA

DIVISION OF BUILDING RESEARCH

SENSlTlVlTY

IN

LEDA CLAY

BY

EDWARD PENNER

REPRINTED FROM

NATURE. VOL 197, NO. 4865. JANUARY 26, 1963. P. 347

-

348.

RESEARCH PAPER NO. 1 8 1

OP THE

DIVISION OF BUILDING RESEARCH

PRICE 10 C E N T S OTTAWA APRIL 1963

T h i s p u b l i c a t i o n i s being d i s t r i b u t e d by t h e Division of Building R e s e a r c h of the N a t i o n a l R e s e a r c h Council. It should not be r e p r o d u c e d in whole o r i n p a r t , without p e r m i s

-

s i o n of t h e o r i g i n a l p u b l i s h e r . T h e Division would b e glad to be of a s s i s t a n c e i n obtaining s u c h p e r m i s s i o n .

P u b l i c a t i o n s of the Division of Building R e s e a r c h m a y be obtained by m a i l i n g the a p p r o p r i a t e r e m i t t a n c e , ( a Bank, E x p r e s s , o r P o s t Office M3ney O r d e r o r a cheque m a d e p a y - a b l e a t p a r in Ottawa, to the R e c e i v e r G e n e r a l of Canada, c r e d i t National R e s e a r c h Council) t o the National R e s e a r c h Council, Ottawa. S t a m p s a r e not a c c e p t a b l e .

A coupon s y s t e m has been i n t r o d u c e d to m a k e pay- m e n t s f o r publications r e l a t i v e l y s i m p l e . Coupons a r e a v a i l - a b l e i n d e n o m i n a t i o n s of 5, 2 5 and 50 c e n t s , and m a y be ob- tained by m a k i n g a r e m i t t a n c e a s indicated above. T h e s e coupons m a y be u s e d f o r the p u r c h a s e of all N a t i o n a l R e s e a r c h Council publications including s p e c i f i c a t i o n s of the Canadian G o v e r n m e n t S p e c i f i c a t i o n s B o a r d .

(Reprinted from Nullire. Vol. 197, N o . 4865, pp. 347-348,

Jntz~lnry 26, 1963)

SENSITIVITY IN LEDA CLAY

By EDWARD PENNER

Soil Mechanics Section, Division of Building Research. National Research Council, Canada

T

HE sensitivity (ratio of tho natural strcngth to t h e remoulded strength) of Norwegian marine sediments reported in the literature' shows an inverse relationship t o the existing salt concentration of the pore watcr. These findings arc explained hy tho 'leaching theory' of sensi- tivity-hich is based on the premise t h a t sedimentation toolr placo in soa-water or brackish water. The decrease in the salt concentration of poro water by subsequent leaching and/or diffusion causes t h e salt-flocculated structure to become 'metastable'. This red~ices t h e remoulded strength much more t h a n the natural strength. The marine sediments of thc St. Lawrence Lowlands (commonly referred t o as Leda clay) are similar to t h e Norwegian sediments in clay mineral composition3-% I n both soils unaltcrcd particles of similar minerals malre up a consiclerable proportion of all size fractions. There are also similarities in many of the gcotechnical properties the soi13~"nd in the phcnomenon of frequent a n d sudden earth flow slides in such deposits. The most characteristic property of both soils is the largo loss of strcngth whcn rcmoulded. To date, hotvcver, it has n o t been possible t o establish for Leda clay how nlucll of tho sensitivity can bc attributed to the leaching of salts or t,o what extent othcr fk~ctors are involvcd.

Certain provious obscrvations may be recounted since they support this aspect of dissimilarity betwecn t h e Norwegian and Leda clays regarding sensitivityj. I n t h e Ottatva area thc porc water salt concentration of Leda clay is generally a fraction of a gram per litro a n d rarely cscceds 1-2 g/l. ( I n contrast, a wide range of pore water salt conccntrations has been rcportcd for Norwegian marine clays.) A t the same timc the sensitivity may vary from a low valuc of 10 to values of 200 and higher deponding on how it is measured7. Usually, high sensitivities are accompanied by low plasticity indices and low liquid limits, and low scnsitivities with higher plasticity indices a n d liquid limits, quite inclopondent of salt conccntration. Thero is also a tcnclency for tho most sensitive portions of the profile to be more silty in nature although t h e diffor- ences are somctimcs small or negligiblo.

I n other studies bcing carried out on LC& clay from a deep excavation, radical changes were observed in

I I

0 0.5 1.0 1.6 2.0

Salt added (gi100 g dry soil)

Fig. 2 . I~cmouldcd strennth of 94-30 as a function of elccholyte content

a t the fleld mo~sture content

A F T E R

S O D I U M CARBONATE

.._.___.____C----

__.-

Sample No.

Undisturbed strengtli (falling cone) Remoulded strength (falling cone) Scnsltivlty

Geodetic elev. Depth below surfaee 3Iechanical an;~lgws c 2 p (clay sizc) 2-20p (silt size) > ?Or6 Liquid limit Plastic limit plasticity index

Salt concentratloll (pressure ex- traction of pore water) Dry density (held) Surface area (glycol mcthod)

Cation excl~nuge capacitv

%:turn1 nloisture content

Water contcnt at cquivnlcnt strengths

Cation content (leached 5 g soil

with 200 C.C. of llnlmoniunl ncctatc) Ca 31g I< N a

ltatio, surfacc arcalper ccnt clay

1,030 Ib./ft.? 1.3 Ib./ft.' 1,500 124 ft. 47 ft. 71 per cent 29 per cent 0 30 24 15 1.1 011. 66.<lb./ft.~ 53.7 m2/g 1 G . O rn.eqaiv./lOO 6.1 65.6 per ccnt 55.6 pcr ccnt 0.35 g/lOO g soil 0.09 g/lOO g soil 0.09 g/lOO g soil 0.17 g/100 g soil 04-13 2 OSO lh /ft."

GB

~b./ft:: 30 140 ft. 22 ft. 3 3 pcr ccnt, 1 3 per ccnt 0 GO 31 36 0.6 nil. 01.7?lb./ft." 72.0 m'/g g 15.0 n1.equir.1100 g 8.1 65.2 pcr cent 136 per cent 0.40 p/lOO g soil 0.12 g/lOO g soil 0.07 g/100 g soil 0.04 ./lo0 g soil

sensitivity in the absencc of any large changes in the pore water salt concentration. With samplcs from strata of high ancl low sensitivity esploratory determinations were carried out in an attempt t o cstablish other rcasons for this apparently anomalous situation a s comparcd with Norwegian clays.

The results given in Table 1 show t h a t there are only small differences between the two samples with respect t o percentage clay- and silt-sizc particles, surface areas, cation exchange capacity! low salt concentration, natural water content ancl pH. Thc large diffcrcnces are in the behaviour of the materials as measured b y the Atterberg limits and, of conrse, in sensitivity. The water content of sample 94-13 had t o be increascd t o 136 per cent before i t reached the low remoulclcd strength t h a t sample 94-30

had a t its natural moisture content of 55.6 per cent. When electrolyte was added, each samplc showed t h e same trend in strength bchaviour although there were large differences in the magnitude of the response. Fig. 1

shows the drop in strength resulting from additions of sodium metaphosphate (this conlpound has a 1 - 1 mole ratio of Na,O/P,O,) after remoulding the samples mechan- ically. These strengths were measured with a lightweight drop cone 1 min after mising was stopped. I t is the large change in strcngth of sanlple 94-13 t h a t is of significance when coinpared with samplc 94-30. B y adding 1 g of sodium mctaphosphate per 100 g of soil the strength clropped from 70 lb./ft."o about 1 lb./ft.\ while t h e strength of the more sensitive soil changed by only a fraction of this. At, higher concentrations flocculation

occurred as indicated by the increase in remoulded strength. It is not unreasonable t o assume t h a t the stability of the structure of these two samples was quite different as evidenced by the response to the dispersant. I n the highly sensitive soil, mechanical mixing was s ~ a c i e n t to causo a high degree of dispersion which could only be achievcd in the clay of lomr sensitivity by increasing the electrokinetic potential8 and hence the amount of repulsion between adjacent particles.

Addition of sodium metaphosphate also reduced the liquid limit and plasticity index. Sample 94-13, originally with a liquid limit of 68.9 per cent, was reduccd to 67 per cent a t 0.022 g of sodium metaphosphate per litre of p o ~ e water to 63 per cent a t 0.09 g/l. and t o 53.7 per cent at 0.26 g/l.

Fig. 2 sho~vs changes, measured in shear strength, of sample 94-30 by increasing the electrolyte concentration ~ v i t h various salts a t natural moisture content. With calcium chloride, sodium carbonate and sodium chloride the strength increased but with sodium metaphosphate the strcngth decreased. This behaviour can bc explained in terms of the effect that changing the inteilx~rticle force has on structural arrangementQnd this is consistent with the behaviour of Norwegian marine clays1.

The higher sodium content of the lcachate from 94-30 (Table 1) may be of significance in assisting more complete dispersion while rcmoulding and in this casc may cxplnin the difference in sensitivity bet~veen these two samples. There are apparently factors, therefore, other than rcduc- tion of the pore ~ v a t a r salt concentration of sediments that have led t o the present variation in sensitivity in Leda clay.

Illerrurn, L., GdoteeRniqlie, 4, 49 (1967).

* Rosenqrist, I. Th., ~ 1 I ~ d d e l ~ l s e r jra Vegdirekto~en, S o . 3, 29 (1946).

.' Rosenqvist, I. Th., Korzcegiaiz Geoteel~. Inst., Piib. Xo. 9 , Oslo (1955).

' D r y d o n , J. E., and Patry, L. 31., Canad. J. Soil Sci., 41, 2, 169 (1961).

"den, W. J., niid Crawford, C. B., Proe. P o f w t l ~ I ~ i l o r l ~ . Soc. Soil Mecir.

Pound. Eng., 1 , 22 (1957).

"rawford, C. B., in Soils i t ! Canada, Roy. Soc. Canada, Spec. Pub. No. 3

(Univ. Toroilto Press, 1061).

' Edcn, TV. J., and Kubota, J. X., Proc. Amor. Soc. T ~ s l ~ n g Mad,'., 61, 1239

(1961).

T o n Wnacr, J. R., Phosphorus and its Con~pounds, 1, 466 (Intcrsciencc

I'ublisliele, Inc., New York, 1966).

Warltcntin, B. P., A ' a t i ~ r ~ , 190, 267 (1961).

--