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THE EFFECT OF COMPACTION AND ADDITION OF LIME ON A LATOSOL

A. Chauvel' , M . T. de Nobrega= and D. Tessier

'Orstom - I n s t i t u t o de Geociencias, USP, Brazi l ' I n s t i t u t o de Geociencias, USP-ABE,' Braz i l ' Ins t iku t Nat ional de l a Recherche Agronomique, Versa i l les ,

3

France I

BSTRACT '

Micromorphology has been used t o s tudy t h e s t a b i l i s a - t i o n of clayey mater ia l from oxic B horizons of f e r r a l l i t i c s o i l s f o r purposes of c i v i l engineering construct ions.

The mater ia l i n its n a t u r a l s t a t e and a f t e r compaction i n the moist s t a t e with and without t h e addi t ion of 5% hydrated lime was examined with t h e o p t i c a l and scanning e l e c t r o n microscope.

i ca l methods of s o i l mechanics (Proctor t e s t s and measure- ments of shrink-swell , Cal i fornia bearing r a t i o , and perm-

The mechanical behaviour was examined using t h e class-

e a b i l i t y and c a p i l l a r i t y ) . The addi t ion of 5% lime completely modified t h e

e f f e c t s of t h e physical t reatments (mixing, wet t ing, comp- a c t i n g ) . When these t reatments a re appl ied t o t h e n a t u r a l s o i l mater ia l t h e microstructure is destroyed but t h e mineral cons t i t uen t s remain in t ac t . a r e appl ied a f t e r addi t ion o f 5% lime, there is a ' f o s s i l - i s a t i o n ' of s t r u c t u r e s of pedological o r i g i n but a t t h e same time a p a r t i a l a t t a c k on t h e mineral cons t i t uen t s and neoformation i of calcium a luminos i l ica tes ,

When the t reatments

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INTR ODUCT I Q N

ma te r i a l from an oxic B horizon (So i l Survey S t a f f , 1975) (clayey l a t o s o l i c B horizon, Comissao de Solos , 1960). Examinations were made,of samples with and without t h e add i t ion of 5% hydrated lime added as a s t a b i l i s e r .

Study us ing o p t i c a l and scanning e lec t ron micro- scopes was made of both natural undisturbed mater ia l s (Fig. l a and d ) and of samples subjected t o t h e Proctor t e s t at an 'optimal Proctor moisture' (27 t 0 . 3 6 water f o r t h e mater ia l s tud ied) with t h e addi t ion of lime (Figs. IC, 2a, c , d and ,e) and without t h e addi t ion of lime (Figs. l b t o e and 2b). Thin sect ionswere a l l v e r t i c a l 1 ' en ted ,

Micromorphology was used t o Study t h e behaviour of

ia%iR. f9& 237 O. R.S.T. O. M. Fonds Documentaire

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9

5

A. Chauve1 et al.

Fig.1. .

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L

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ADDITION OF LIME 239

parallel to the compacting axes. was studied by classical methods of soil mechanics: Proctor test, shrink-swell test , Calif ormia Bearing Ratio (CBR) , permeability and capillarity tests. the first two are presented here (Figs. 3 and 4).

The mechanical behaviour

Only the results of

COMPACTION C)F UNLIMED SOIL MATERIAL Compaction caused modification of the fabric at dif-

ferent levels of organisation but no change in the nature of the constituents:

- The initially argillasepic plasmic fabric is modified on compaction, with development of plasmic separations, stress cutans and fine plane fissures perpendicular to the compacting axis.

- The related distribution (Stoops and Jongerius, 1975) characterised initially by a micropedal arrangement (porphy- enaulic re lat ed distribution pattern) changes due to aggregate coalescence into a continuous mat-- erial of porphyriz type.

- The natural porosity consisting of a network of pack- ing votds is replaced by a series of sub-parallel meta-joint planes along which there may be slicken- sides

finger Fressure into a granularr/single grain structure is converted to a continuous structure divided into

Fig. l(a.-). Natural material. forous framework formed by continuous assembly of micropeds. ant and skeleton grains are rare, mainly opaque minerals and some quartz. voids. SRDE agglutinic. XPL; (b) Compacted material, continuous structure divided into lamellae by stress cutans and fissure voids perpendicular to the compact- ing axis. addition. Crystallisation of calcium aluminous silicate in the packing voids. XPL; (d) SEM micrograph of natural material. Interconnected packing voids ; (e) Compacted material.

- A micropedal, very porous structure breaking under

Plasma is domin-

Interconnected packing

PPL; (c) Compacted material after lime Conservation of the porous framework.

Porous framework formed by micropeds.

- - Microped - coalescence. Joint plane formation. SymbÖl key : C -cutgn; - ZalcTum äluïnoüs gil: - cate; L - lamellae; M - micropeds; MO - opaque miner- als; P - plasma; Q - quartz; V - voids

I , I

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4

240

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A. Chauve1 e t al.

Fig. 2.

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ADDITION CIF LIME 241

f i n e lamellae. I n its n a t u r a l condi t ion, the s o i l is very s t a l e pro-

vided no mechanical s t r e s s i s applied. However, a f t e r t h e appl ica t ion of force (Proctor normal f o r c e ) , the mater ia l becomes s t rongly compacted and its bearing index increases (CBR = 1%) but at t h e same time becomes sens i t ive t o water a c t i o n r e f l e c t i n g t h e clayey nature of i t s const i tuents . Tn response t o f o r c e s of i n t e r n a l o r ex te rna l o r i g i n , the lamellae may become dis located by s l i p g i n g over one another.

THE EFFECT 9F LlPE ON COMPACTION

s o i l s t o which lime has been added a r e compacted than when t h e s o i l contains no added lime. I n a d d i t i o n , i n the limed s o i l t h e r e is neoformation of calcium aluminous s i l i c a t e from the d isso lu t ion products of t h e s o i l const- i t u e n t s ( A l , S i ) and added calcium.

The plasmic f a b r i c and r e l a t e d d i s t r i b u t i o n p a t t e r n of t h e o r i g i n a l f e r r a l l i t i c s o i l a r e r e s i s t a n t t o compac- t i o n i f lime is added. The micropeds which charac te r i se t h e o r i g i n a l s t r u c t u r e become ‘ f o s s i l i s e d ’ by calcium aluminous s i l i c a t e c r y s t a l s forming on t h e i r surfaces and wi th in in te rpedal voids. i n crystallaria formed a f t e r liming.

r e s i s t a n t t o water ac t ion and its bearing capacity increas- e s by a f a c t o r o f f i v e . .

The inher i ted s o i l f a b r i c is b e t t e r preserved when

The peds thus become enmeshed

The mater ia l a f t e r t h e addi t ion of lime is much more

, .(

I’ ? e L -

Fig .2 (a’) SEM micrograph of compacted mater ia l a f t e r lime addition. Conservation of micropeds. Surface aspect very broken. (b) Compacted material . Planar microvoids roughly perpendicular t o t h e compacting axis; ( c ) Compacted mater ia l a f t e r lime addition. Conservation o f micropeds separated by assembly of po lycrys ta l l ine p a r t i c l e s . Interconnected mesovoids; (d). Compacted mater ia l a f t e r lime addi t ion. Micropeds and framework formed by assembly of po lycrys ta l l ine p a r t i c l e s and micropeds; (e ) Detai l o f (a). Assembly of po lycrys ta l l ine p a r t i c l e s and micropeds; (f ) Material of experimental road, Crystallaria of calcium

- - - aluminous s i l i c a t e s i n voids. SymToT key :- A 3 --pay&y&all&ë Gr%i<lës i@ - - polycrystal l ine p a r t i c l e s ; M - micropeds; V - voids

242

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A. Chauve1 e t al.

rd d c m 3 C 0 R - 1 0 % ____ without lime _ _ _ with l ime 1.600

(n I

-$ C l 1.500

/ i

/

\..

Q

1.400..

C BR -54%'\.

. \ ,.--.

\ '., '\

t Water content 1.300

18 20 22 24 26 20 30 32 34

Fig.3. Note f l a t t e n i n g of curve, mater ia l is l e s s compacted and the maximum Proctor is displaced toward a l e v e l of g rea te r moisture.

@Sect of lime addi t ion on t h e Proc tor curve.

C ONC LUS I O N

the s t a b i l i s a t i o n of l a t o s o l s by t h e addi t ion of lime i s of ul t imate value i n improving t h i s approach f o r c i v i l engineering constructions. t o t a l l y changes t h e e f f e c t s of compaction i n a wet s t a t e . Compaction of mater ia l without added lime destroys t h e o r i g i n a l microstructure but does not modify t h e mineral const i tuents . there is f o s s i l i s a t i o n of t h e pedological organisation.

A b e t t e r knowledge of t he mechanisms responsible f o r

The introduct ion of a r eac t an t

~y con t ra s t , i n ' mater ia l containing 5% lime

b c

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ADDITION OF LIME

Yd g/cm3

2.0 I _ _ _ with lime ( 5 % ) ____ without lime

243

Water content O 18 20 22 24. 26 28 30 32 34

g Hz0 /i00 g solid

Fig.4. compaction a t d i f f e r e n t moistures; with lime addi t ion there is l i t t l e f u r t h e r shrinkage above a moisture l e v e l of 24%.

Effect of lime addi t ion on t h e shrinkage a f t e r

ACKNOW LEDtTEMENTS The authors thank J. Berr ie r (Laboratoire des S o l s

INRA , Versa i l les ) f o r col laborat ion i n scanning e lec t ron microscopy and microprobe analysis .

This work has been car r ied out under an agreement between ORSTOM and C N Q (Brazil) . t h e mater ia l support of the Brazi l ian Association of Lime Producers.

It has benefited from

REFERENCES Comissao de Solos , 1960. Levantamento de reconhecimento

dos s o l o s de Estado de Sao Paulo, Ministerio da Agricultura, CNEPA, SNPA, 12, 634 pp.

s o i l c l a s s i f i c a t i o n f o r making and in te rpre t ing s o i l surveys. USDA, A g . Handbook 436, Washington D.C.

Stoops, G. and Jongerius, A. 1975. Proposal f o r a micro- morphological c l a s s i f i c a t i o n of s o i l material. I. A c l a s s i f i c a t i o n of t h e r e l a t e d d i s t r i b u t i o n s o f f i n e and coarse p a r t i c l e s . Geoderma, 13, 189-199.

S o i l Survey Staff. 1975. S o i l Taxonomy, a basic system of

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Techniques and Applications

Editedby ,

P Bullock and C P Murphy Rothamsted

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