Mechanical improvement and vertical yield stress prediction of clayey soils from eastern Canada treated with lime or cement

Mechanical improvement and vertical yield stressprediction of clayey soils from eastern Canadatreated with lime or cement

Hlne Tremblay, Serge Leroueil, and Jacques Locat

Abstract: The method of soil stabilization is well known and has been used throughout the world for many decades toimprove some soil properties. Although many researchers have studied the effect of adding a cementing agent to a soil,not many of these researchers have explored the effect of treatment on the resulting properties of high water contentsoils like dredged material. Also, there has been little work concerning the prediction of the mechanical changes to thesoil. Therefore, this paper summarizes the results of a research project conducted to define the general mechanical be-havior of high water content clayey soils from eastern Canada treated with lime or cement, in terms of compressibility.In the light of this research, the general compressibility behavior has been obtained, defined by relationships betweeninitial void ratio, additive content, and vertical yield stress for a given inorganic or organic soil. These relationshipshave been normalized on the basis of the one-dimensional compression curve of the remolded and reconstituted un-treated soil to give a simple method for predicting the vertical yield stress of a treated soil for any initial void ratioand its resistance to compression.

Key words: stabilization, compressibility, yield stress, clayey soils, lime, cement.

Rsum: La mthode de stabilisation des sols est bien connue et a t utilise depuis plusieurs dcades travers lemonde pour amliorer certaines proprits des sols. Quoique plusieurs chercheurs aient tudi leffet de laddition dunagent de cimentation au sol, peu dentre eux ont explor leffet du traitement sur les proprits rsultantes des sols teneur en eau leve tels que les matriaux dragus. galement, il y a eu peudtudes portant sur la prdiction deschangements mcaniques apports au sol. En consquence, cet article rsume les rsultats dun projet de recherche ra-lis pour dfinir un comportement mcanique gnral en terme de compressibilit de sols argileux hautes teneurs eneau de lest du Canada avec de la chaux ou du ciment. la lumire de cette recherche, on a obtenu le comportementgnral en compressibilit dfini par la relation entre lindice des vides initial, la teneur en additif, et la contrainte deprconsolidation apparente verticale pour un sol donn organique ou inorganique. Finalement, ces relations ont t nor-malises sur la base de la courbe de compression unidimensionnelle du sol non trait remani et reconstitu pour don-ner un mthode simple pour prdire la contrainte de prconsolidation apparente verticale dun sol trait pour nimportequel indice de vide initial, et sa rsistance la compression.

Mots cls: stabilisation, compressibilit, contrainte de prconsolidation apparente, sols argileux, chaux, ciment.

[Traduit par la Rdaction] Tremblay et al. 579

Introduction

Since the early 1960s, soils have been treated with ce-menting agents to improve their geotechnical properties suchas shear strength and resistance to compression (Broms andBoman 1977; Terashi and Tanaka 1981; Bell 1989; Locat etal. 1990, 1996; Rajasekaran and Narasimha Rao 1997). Theeffects of additives are well known, especially for clayeysoils at low water contents, close to their plastic limit. Treat-ment of very soft materials, like dredged slurries, is moreproblematic because of their high water content and often

high organic content. Also, due to unwanted environmentalimpacts, dredged slurries generally cannot be disposed of infree water and must be buried or treated when contaminated.For this kind of material, stabilizationsolidification is an in-teresting method of recovery, making these soils usable forembankments or earthworks; it is not very common in Can-ada, but some countries such as Japan use this materialwidely and effectively (Terashi and Tanaka 1981). Eventhough this method of treatment is widely used throughoutthe world, it is still difficult to predict the improvement ofthe strength or the compressibility of a stabilized soil. Some

Can. Geotech. J.38: 567579 (2001) 2001 NRC Canada

567

DOI: 10.1139/cgj-38-3-567

Received December 24, 1999. Accepted November 20, 2000. Published on the NRC Research Press Web site on May 31, 2001.

H. Tremblay1 and J. Locat. Department of Geology and Geological Engineering, Universit Laval, Sainte-Foy, QC G1K 7P4,Canada.S. Leroueil. Department of Civil Engineering, Universit Laval, Sainte-Foy, QC G1K 7P4, Canada.1Corresponding author (e-mail: [email protected]).

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approaches were proposed to predict the strength gain oflow water content inorganic soils treated with lime (Eadesand Grimm 1966; Perret 1979; hnberg et al. 1989; Locat etal. 1990), but little attention has been given to the predictionof compressibility.

When present in a soil, organic matter affects some of thesoil properties. It is well known that liquid and plastic limitsincrease with increasing organic matter (Rashid and Brown1975; Bush and Keller 1981; Landva et al. 1983; Bennett etal. 1985; Booth and Dahl 1986). Compressibility also in-creases with an increase in organic matter content (Rashidand Brown 1975). According to some studies (Keller 1982;Booth and Dahl 1986), a minimum quantity of organic mat-ter is necessary to cause a modification in a soil, and thisminimum would be around 34%. Bennett et al. (1985)mentioned that the nature of this organic matter may also in-fluence the effects of organic content on soil properties andnoted that a proportional relationship exists between carbo-hydrates content, water content, and liquid limit. Also,Keller (1974) obtained an excellent relationship betweencarbohydrates content and shear strength.

Some studies indicate that organic matter may interfereduring the cementing process when a cementing agent isadded to the soil. Organic matter coats cement or limegrains, preventing or delaying their hydration reaction(Kamon et al. 1989). It seems, however, that only some ofthe organic components really hamper the cementing pro-cess. For instance, Kamon et al. (1989) and Tremblay (1998)mention that humic acid strongly delays the hydration pro-cess. Nonetheless, many experiments have demonstrated thatorganic soils and peat can be successfully treated with dif-ferent cement mixtures (Holm et al. 1983; Ogino et al. 1994;Parkkinen 1997; Hoikkala et al. 1997; Gulin and Wikstrm1997; Den Haan 1998).

This paper summarizes the results of a research project onthe improvement of both inorganic and organic, high watercontent remolded clayey soils from eastern Canada whentreated with lime and cement. The objectives were to estab-lish a general compressibility model and develop a methodto predict the vertical yield stress. Seven soils were tested,four inorganic and three organic. They were treated with hy-drated lime or Portland cement and prepared at different wa-ter contents corresponding to liquidity indices between 1 and14. After a curing period of between 30 and 100 days, thedifferent mixtures were subjected to one-dimensional com-pression tests and their compressibility curves were thencompared. Using these results, typical behavior in terms ofcompressibility and an approach for predicting the verticalyield stress of treated soils are presented.

Tested soils and experimental procedures

Tested soilsSoils were chosen to cover a wide range of some specific

properties. As clayey mineral content seems to control thebehavior of treated soils (Le Roux 1969; Bell 1976;Choquette et al. 1987; Rogers and Glendinning 1996), andas clayey mineral content of eastern Canadian soils isclosely related to the percentage of clay particles (m)(Bentley and Smalley 1978; Lebuis et al. 1982; Locat et al.1984; Locat 1995), the clay fraction was chosen as the maincriterion for soil selection.

The seven tested soils can be divided in two groups: fourinorganic soils, including the Louiseville, St-Alban, andJonquire clays and the Trois-Rivires silt; and three organicsoils, including dredged material from Qubec harbor, Portde Qubec recent sediments, and Saguenay Fjord sediments.All soils are from the province of Quebec. The Louisevilleand St-Alban clays are postglacial Champlain Sea marineclays, and the Jonquire clay originates from postglacialLaflamme Sea. The Trois-Rivires silt is a fluvioglacial de-posit. Thedredged material is a sediment dredged from Qubecharbor in 1988 and stacked on land since then (Tremblay1998). To compare this material with newly dredged mate-rial, sediments from the Qubec harbor were recovered justbefore the testing program. These sediments are called Portde Qubec sediment herein. The organic matter is less de-composed in the Port de Qubec sediment than in thedredged material. The Saguenay sediment was recovered fromthe bottom of Saguenay Fjord (Perret 1995; Perret et al.1995). The organic matter in the Saguenay sediment is verydecomposed compared to that of the two other organic soils.

The main physical characteristics of the tested soils arepresented in Table 1. The liquid limits vary from 22 to 86%and the plastic limits from 0 to 34%. The specific gravityvaries from 2.65 to 2.78, and clay content (m) ranges from8 to 80%. The organic matter content for the inorganic spec-imens is less than or equal to 1% and varies from 6 to 8%for organic soils. Artificial mixtures were prepared to betterevaluate the effect of organic matter. To do so, some speci-mens of dredged material were tested with an organic mattercontent varying from 0 to 8%. To prepare the different speci-mens, a portion of the soil sample was treated with hydrogenperoxide (H2O2) to completely destroy the organic matter(Booth and Dahl 1986). After this treatment, different mix-tures were prepared with the natural dredged material to ob-tain the desired organic matter contents, between 0 and 8%.

The mineralogical components of the tested soils are quitesimilar for all the tested soils. They include, in decreasing

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Characteristic Louiseville Jonquire St-Alban Trois-Rivires Saguenay Port de Qubec Dredged material

Liquid limit (%) 72 55 44 22 86 65 60Plastic limit (%) 27 24 18 15 34 34 npa

Plasticity index (%) 45 31 26 7 52 31 0Organic matter (%) 1

proportion, plagioclase, quartz, K-feldspar, amphibole, car-bonates, and phyllosilicates (St-Gelais 1990; Locat 1995;Tremblay 1998). Clay minerals are mainly illite and chlorite.

AdditivesTwo different additives were used in this study: hydrated

lime and ordinary Portland cement. The inorganic soils weretreated with lime (Louiseville, St-Alban, and Jonquireclays, and Trois-Rivires silt) and ordinary Portland cement(Louiseville clay and Trois-Rivires silt), and the organicsoils (dredged material, Port de Qubec sediment, andSaguenay sediment) with Portland cement only. Some or-ganic samples were also treated with lime, but as the stabili-zation was not very effective, lime was abandoned for therest of the study on organic soils.

One-dimensional compression testsSeveral specimens were prepared for each selected soil.

First, the samples were completely remolded and then tapwater was added to subsamples in different quantities to ob-tain different water contents. For each water content, 0, 2, 5,and 10% (by dry weight %) of lime or cement was added.The specimens were divided into two groups depending onthe preparation method. The first group of specimens weredeposited in oedometer rings (51 mm diameter and 19 mmhigh) on a porous stone without any compaction effort. Afterplacement in the rings, a vertical stress of 8 kPa was appliedto the samples. Then, they were cured under these conditionsfor 3050 days when treated with lime and 30 days whentreated with cement. Lastly, the samples were submitted tooedometer tests with 50% pressure increments every 24 h.They are considered as low water content specimens withwater contents (w) corresponding to liquidity indices (IL)ranging from 1 to 4 (Table 2). For the second group of speci-mens, the soil was prepared in large Plexiglas cells, calledSEDCON cells (20 cm diameter and 29 cm high) (Perret1995; Locat et al. 1996), at high water contents correspond-ing to liquidity indices of about 14. After self-weight set-tling until stabilization of the height, they were loaded up toa vertical effective stress of 8 kPa. After a curing time of100 days, subsamples were taken and trimmed to carry outconventional 24 h oedometer tests. During curing, all thespecimens were submerged and maintained under an appliedvertical stress of 8 kPa. This stress was chosen to simulate a2 m thick embankment of treated material.

The Trois-Rivires silt, the dredged material, and the Portde Qubec sediment were not tested at high water contentbecause of their high proportions of sand, which may settlein such conditions. To avoid segregation, the specimens wereprepared at a maximum water content corresponding toaboutIL = 3. The dredged material was the only organic ma-terial prepared in a large SEDCON cell, but was prepared ata low water content only (IL = 1.8).

Mechanical behavior of stabilized inorganicsoils

One-dimensional compression tests resultsThe four inorganic soils were subjected to oedometer tests

with various water and additive contents. The results are pre-sented in Fig. 1. The curves show the effect of initial voidratio (e) after curing on the vertical yield stress. For exam-ple, for the Louiseville clay (Fig. 1a) treated with 10% limecontent, the vertical yield stress was 25 kPa (arrows inFig. 1a) for a high void ratio (about 9.8 after curing),whereas it was 300 kPa at the lower void ratio (about 3.3).

It also appears that the normal compression curves (in thenormally consolidated range) obtained for a given soil withthe same lime content but with different void ratios define aline that is independent of the initial curing void ratio. Thisis well illustrated with the Jonquire clay treated with 5%lime (Fig. 2). All the compression curves, in the normallyconsolidated range, join a unique compression curve, inde-pendent of initial curing void ratio. Below this curve, thetreated soil behaves as an overconsolidated material withsmall compressibility. Also, this curve provides a good esti-mate of the vertical yield stress at which the soil starts de-veloping large strains for any initial void ratio, when treatedat an additive content of 5% lime. This behavior was previ-ously observed and discussed by Tremblay (1998) andTremblay et al. (1998) for inorganic soils treated with limeand Portland cement and by Locat et al. (1996) for theLouiseville clay only. The curves obtained for theLouiseville clay treated with ordinary Portland cement arepresented in Fig. 3 and show similar behavior.

General compressibility behaviorAs shown in Figs. 13, the normally consolidated portion

of the compression curves for a given additive content mergevery well. The normal compression curves for each soil, in-cluding the normally consolidated portion of the compres-sion curves for each void ratio, are shown in Fig. 4 forvarious lime contents. These curves define the general be-havior of these treated inorganic soils in terms of compress-ibility. The fan-shaped spread of the curves at differentadditive contents for a given soil depends on the range ofvoid ratios considered, and also on the plasticity of the soil.In fact, the more plastic the soil is, the higher the initial voidratio for a given liquidity index, and the more important isthe spread of the curves. To illustrate this, the relation be-tween the void ratio after curing and the plasticity index (IP)is shown in Fig. 5 for the different lime contents. This graphshows that the influence of plasticity on initial void ratio ismore important as the additive content increases. TheLouiseville clay is the most plastic soil (seeIP = 45% inFig. 5) and shows the greatest amount of spread (Fig. 4a),

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Oedometer rings

Set 1 Set 2 SEDCON cells

w (%) IL w (%) IL w (%) ILLouiseville 122 2.1 650 13.8Jonquire 86 2.0 144 3.9 460 14.1St-Alban 60 1.6 95 3.5 380 13.9Trois-Rivires 25 1.4 35 3.1Dredged material 55 1.0 70 1.2 110 1.8Port de Qubec 110 2.4Saguenay 130 1.9 152 2.3

Table 2. Initial water contents (w) and corresponding liquidityindices (IL) of tested soils for curing in oedometer rings andSEDCON cells.

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with void ratios between 2 and 9. On the other hand, thelow-plasticity Trois-Rivires silt (Fig. 4d) has the smallestrange of void ratios (from 0.67 to 0.98; seeIP = 7% inFig. 5). The St-Alban and Jonquire clays have similar plas-ticity and show similar normal compression curves.

Figure 4 also shows that, even under high stresses, thenormal compression curves obtained for different additivecontents remain separated with a void ratio under a givenstress increasing with an increase in lime content. This indi-cates that, even at high stresses, the treated soil retains a

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Fig. 1. One-dimensional compression curves of selected inorganic soils treated with lime: (a) Louiseville, (b) St-Alban, (c) Jonquire,and (d) Trois-Rivires. The arrows indicate vertical yield stress.

Fig. 2. Example of compression curves of Jonquire clay treatedwith 5% lime and prepared at different void ratios.

Fig. 3. Compression curves of Louiseville clay treated with 5%Portland cement.



memory of the fabric and the structure developed at muchhigher void ratios. It also indicates that the amount of limedictates the degree of bonding strength generated which isnot totally destructured under high stress. This is shown

schematically in Fig. 6, for a given soil, with normalcompression curves associated with different additive con-tents. From the aforementioned observations, we can nowderive a conceptual model which illustrates that for a givensoil we can identify a vertical yield stress obtained for agiven void ratio of a mixture prepared at a given lime con-centration and cured for 100 days.

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Fig. 4. Composite normal compression curves of inorganic soils at different lime contents: (a) Louiseville, (b) St-Alban, (c) Jonquire,and (d) Trois-Rivires.

Fig. 5. Relationship between void ratio after curing under an ap-plied stress of 8 kPa (eo) and plasticity index of tested inorganicsoils.

Fig. 6. Schematic normal compression curves for an inorganicsoil treated at different lime contents.



Figure 6 provides the vertical yield stress, for a given voidratio and additive content, which if exceeded gives rise tothe development of important plastic strains. This figure isthus a potential tool for design. However, the diagram is soilspecific, and the positions of the different curves must be de-termined for each soil. Thus, to predict the resistance tocompression of a treated soil, it would be interesting to ex-plore the possibility of establishing a model that generalizesthe behavior of any inorganic soil.

Conceptual model to estimate the resistance tocompression of treated soils (vertical yield stress)

The void ratio yield stress additive content relation-ships such as those presented in the previous section arevalid for a given soil and vary from soil to soil depending onthe physical characteristics of the soil such as plasticity andmineralogy. Since the one-dimensional compression curvesof untreated specimens are different for each soil (Fig. 1), itappears difficult to compare compression curves of treatedsoils. First, a basis for comparing untreated soils must be de-fined. Burland (1990) proposed a normalization method thatis useful to correlate natural soils in their remolded state andevaluate their degree of structuration. This method normal-izes the compression curves of natural and reconstitutedsoils using a parameter,Iv, called the void index and definedas follows:

[1] Ie e

e ev =

100

100 1000

** *

where e100* and e1000* are the void ratios on the intrinsiccompression line corresponding to vertical effective stressesof 100 and 1000 kPa, respectively (Figs. 7a, 7b) (the asteriskis used to denote an intrinsic parameter). For the purposes ofthe present study, Burlands void index has been modified tobe more relevant to the range of stresses considered for verysoft clayey materials. The modified void index,I v , is definedas

[2] Ie e

e ev =

10

10 100

** *

where e10* and e100* correspond to stresses of 10 and100 kPa, respectively, on the intrinsic compression curve.With this normalization, all the curves of untreated and re-constituted soils pass through two specific points at (10, 0)and (100, 1) in a log v I v diagram (Fig. 7c), where v isthe vertical effective stress.

All the compression curves, previously presented inFig. 1, have been normalized this way and are shown inFig. 8. The objective of this normalization is to compare thenormal compression curves (previously presented in Fig. 4)of the different tested soils at specific additive contents, aspresented in Fig. 9. For untreated specimens (Fig. 9a), allcurves fall on the same line passing through points (10, 0)and (100, 1) in the log v I v diagram. At 2% lime con-tent (Fig. 9b), all the curves fall in a relatively narrow range(see shaded areas). At 5 and 10% lime contents (Figs. 9c,9d), three of the four curves also fit in a narrow range; partof the Louiseville clay curves falls out of the shaded areas,and this is more pronounced as the lime content increases.However, at high vertical effective stress of about 100 and

1000 kPa for 5 and 10% lime contents, respectively, theLouiseville curves fit well with the others. The difference inbehavior of the Louiseville clay at 5 and 10% lime contentsseems to be due to its high plasticity that involves a veryhigh void ratio for the same liquidity index when comparedwith other soils. In fact, as plasticity increases, the initialvoid ratio also increases, as previously shown in Fig. 5.Thus, with a large difference in initial void ratio between thedifferent soils treated at a same lime content, the slopes ofcurves, defined as the compression index, are higher for themore plastic specimens. Consequently, the slopes of the nor-mal compression curves are higher. Nonetheless, the shadedareas seem to provide a lower limit for the normalized nor-mal compression curve which can be used to estimate thevertical yield stress at a given lime content.

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Fig. 7. Intrinsic compression curves: (a) as defined by Burland(1990), (b) void index as defined by Burland, and (c) modifiedvoid index used in the present study.



To eliminate the scatter due to high void ratios for theLouiseville clay specimens treated with 5 and 10% lime, themodified void index,I v , can be normalized again.I v hasbeen divided by the ratio between treated soil void ratio anduntreated soil void ratio at the same vertical effective stress.The new void index is termedI vn and defined as follows:

[3] II

e e

e e

e eeex

xvn

v = =/ *

*

* **10

10 100

whereex* is the void ratio on the intrinsic one-dimensionalcompression curve of the untreated and reconstituted soil un-der a vertical effective stressx, and e is the correspondingvoid ratio for the treated soil. As the difference between thetreated specimen void ratio and the untreated specimen voidratio at the same stress increases, the ratioe/ex* also in-creases. Whene/ex* increases,I vn is reduced. Therefore,this operation allows the Louiseville clay curves to mergewith the others and thus eliminates the dispersion. As shownin Fig. 10, when drawing the normal compression curves inlog v I vn diagrams, the curves all lie on an essentiallyunique curve for a given additive content (broken lines inFig. 10). The small graph in Fig. 10a illustrates the determi-nation ofe andex* for the second normalization. Once plot-ted together in the same diagram, these average normalized

curves clearly show the effect of lime on the vertical yieldstress (Fig. 11). In the graph shown in Fig. 11, the gain issignificant when the lime content increases from 0 and 2%,and relatively small for higher lime contents. The graph alsoshows that the slopes of the curves are quite similar.

The proposed model provides an estimated value of maxi-mum void ratio that would give an expected vertical yieldstress at any lime content using the following derivation.From eq. [3],

[4] Iee e ee e e e

e ee e

ee

x xx

x

vn =

=

* * *

* *

** *

10

10 100

10

( * *)e e10 100

With a reorganization of terms,

[5] I e e ee e

ex

xvn = ( * *) *

* *10 100

10

and we obtain the equation

[6] e ee e

e I e I ex

x

= = +

max* *

* * *10

10 100vn vn

where emax is the maximum void ratio admitted to reach agiven vertical yield stress.

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Fig. 8. Normalized compression curves of inorganic soils at different lime contents: (a) Louiseville, (b) St-Alban, (c) Jonquire, and(d) Trois-Rivires.



The suggested method could then be summarized by thefollowing steps:

(1) Determine the one-dimensional compression curve ofthe considered soil, reconstituted with a water content corre-sponding to a liquidity index of about 3 to ensure having anatural compression curve with the highest possible void ra-tio. Locat (1982), Perret (1995), and Tremblay (1998) haveshown that there exists a maximum void ratio for a givensoil at which the untreated specimens stabilize after consoli-dation under a small stress, even for a very high initial voidratio.

(2) Definee10* and e100* using the curve obtained in step1.

(3) Using Fig. 11, evaluate the value ofI vn correspondingto the desired vertical yield stress and additive content.

(4) Convert the value ofI vn from step 3 into a void ratiousing eq. [4] which provides the maximum void ratio thatwould allow the desired vertical yield stress to be reached.The values ofe10*, e100*, and ex* are taken on the compres-sion curve of the reconstituted untreated soil for 10 kPastress, 100 kPa stress, and the desired vertical yield stress,respectively.

An example of the steps previously enumerated is given inFig.12 for Louiseville clay. The first step gives the one-dimensional compression curve of the considered soil, un-treated and in a reconstituted state (Fig. 12a). From thiscurve, the parameterse10*, e100*, and ex* are determined

which correspond to the minimum required vertical yieldstress fixed at 500 kPa for this example (step 2). These val-ues aree10* = 2.25, e100* = 1.48, andex* = 1.10. Figure 11,redrawn in Fig. 12b, then gives the value ofI vn for a verti-cal yield stress of 500 kPa (step 3). TheI vn values are 0.00for 5% lime content and 0.37 for 10% lime content. The laststep is the calculation of the maximum void ratio that wouldgive the desired vertical yield stress at a given lime content,using eq. [4]. The calculated values ofemax are 2.25 and 3.03if the soil is treated with 5 and 10% lime, respectively. Thismeans that if, for example, a soil has a void ratio of 3.0 inits remolded state, it is necessary to treat it with 10% lime toreach a vertical yield stress of 500 kPa, or if the soil has avoid ratio of about 2.0, 5% lime would be enough to obtaina vertical yield stress equal to or slightly greater than500 kPa.

The advantage of this prediction approach in comparisonwith others proposed by Perret (1979), hnberg et al.(1989), and Locat et al. (1990) is that this simple method re-quires only a one-dimensional compression curve, obtainedfrom the remolded natural soil. However, this method mustbe used for preliminary design only. Also, the diagram inFig. 11 is valid only for inorganic eastern Canadian clayeysoils treated with hydrated lime. For additives such as ce-ment, the results obtained up to now indicate a similar quali-tative behavior, but there are too few data to develop adiagram similar to that in Fig. 11 for cement. Also, as only

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Fig. 9. Normalized compression curves for the different lime contents: (a) 0%, (b) 2%, (c) 5%, and (d) 10% lime.



eastern Canadian clayey soil has been tested up to now, it isnot known if Fig. 11 could be representative of other clayeysoils of different mineralogy.

Evaluation of the proposed method

The proposed method (Fig. 11) gives a simple tool forpreliminary design because it gives an estimate of the maxi-mal void ratio (emax) that will give a desired resistance tocompression for a specific lime content. To appreciate the ef-fect of the dispersion of the curves shown in Fig. 10 onemax,some calculations using eq. [4] have been made for soilstreated with 5 and 10% lime and for a desired yield stress of1000 kPa (Table 3). The value ofemax has been calculatedwith the maximum and minimum values ofI vn which repre-sent the extent of the normalized curves, and also with thevalues ofI vn corresponding to the average line on the graphs(broken lines). In comparison, the values of void ratios mea-sured under an applied stress of 1000 kPa at the given limecontent are also given. It appears that the proposed methodgives a good estimation ofemax for this order of magnitudeof stress if we compare the measured values ofe and emaxfor I vn on the average line (broken line). As shown inFig. 10, the dispersion of the curves is variable. It seems thatfor 2% lime, the dispersion increases with increasing stress,whereas for 5 and 10% lime it decreases. In other words,this method is more appropriate for low stress (d kPa), whena small amount of lime is added (such as 2%), and for highstress (500 kPa), when a large amount of lime is added (suchas 10%). With 5% lime, the dispersion is of lesserimportance,

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Tremblay et al. 575

Fig. 10. Compression curves normalized withIvn: (a) 0%, (b) 2%, (c) 5%, and (d) 10% lime.

Fig. 11. Normalized compression curves for reconstituted easternCanadian clayey soils treated with lime.



then the method can be used for a wider range of stresses(between 50 and 4000 kPa).

As previously explained, the yield stress of inorganic east-ern Canadian fine-grained soils can be estimated whentreated with lime. It may be possible to develop an equiva-lent model to predict the yield stress of soils treated with ce-ment because the behavior is similar to that with limetreatment (Fig. 3), but this has not been verified.

Mechanical behavior of stabilized organicsoils

One-dimensional compression tests have been conductedwith organic soils treated with Portland cement at differentwater contents. The results give responses qualitatively simi-lar to those obtained for inorganic soils. In particular, normalcompression curves can be drawn from the compressioncurves obtained at a given additive content and different ini-tial curing void ratios. Some of the results are plotted inFig. 13 for specimens of dredged material prepared at differ-ent organic matter contents varying from 0 to 8% and at two

different water contents for the specimen containing 8% or-ganic matter and treated with 10% cement (Fig. 13b). Theresults for untreated specimens (Fig. 13a) confirm that or-ganic content influences the compressibility of natural soils;the compressibility of the sample containing 8% organicmatter is much higher than those for samples with 0 or 3%organic matter. According to Stevenson (1994), the increas-ing compressibility with increasing organic content is causedby the tendency of organic matter to form complexes withclay particles and then form aggregates, causing an increasein the pore size and consequently an increase in the com-pressibility.

When treated with 10% Portland cement, the effect of or-ganic content on compressibility is less important, since the

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Fig. 12. Example showing the use of the normalized compres-sion curves for Louiseville clay, varying with lime content.

Fig. 13. Compression curves of dredged material containing dif-ferent organic matter contents: (a) untreated, and (b) treated with10% Portland cement.



difference in initial void ratio of the soil with 0 and 8% or-ganic content (Fig. 13b) is smaller than that for the naturalsoil (Fig. 13a). Also, the normal compression curves areabout the same (Fig. 13b). Figure 13b shows that the generalbehavior observed for inorganic soils is also applicable fororganic soils, since the curve of the specimen treated at highwater content joins the curve at a lower water content.

As the normalization method of Burland (1990) is basedon the compressibility of reconstituted soils, it is importantto consider the organic matter content of untreated samplesto normalize treated curves. It therefore appears impossibleto obtain one curve alone for a specific additive content butvarying organic contents because the basis for comparison isdifferent. For example, Fig. 14 presents the normal compres-sion curves corresponding to 0, 3, and 8% organic mattercontents in a log v I v diagram for specimens treated with10% cement. There is significant dispersion of the curves inFig. 14, whereas dispersion was almost negligible for thedifferent inorganic soils treated with a wide range of additivecontents.

Figure 15 shows the normalized curves for samplestreated with 5% Portland cement, and the influence of or-

ganic matter content is again quite clear. In fact, the curvesform two groups, one for specimens containing 3% organicmatter or less, and one for those with 68% organic matter.The same pattern has been observed for specimens of otherorganic soils treated with 10% cement (Tremblay 1998). Asmentioned earlier, the minimum organic matter contentabove which soils are considered organic is about 34% be-cause it is the concentration at which modifications of prop-erties start. According to Keller (1982), with organiccontents lower than 4%, the mineralogy and grain size exerta more important influence on properties than the organicmatter content. The results presented here also confirm achange in behavior at an organic matter content of 34%.Below this value, cementing clearly occurs, whereas theeffect of cement is smaller at higher percentages. The effectof organic matter content is summarized in Fig. 16 in alog v I v diagram. As illustrated, the lines are shifteddownward as organic matter content increases. It seems pos-sible to create a diagram for organic soils to predict the ver-tical yield stress for any initial void ratio at a specificadditive content, such as that in Fig. 11, but this must

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Fig. 14. Average normalized normal compression curves fordredged material containing different organic matter contents andtreated with 10% Portland cement.

Fig. 15. Average normalized normal compression curves for soilscontaining different organic matter contents and treated with 5%Portland cement.

emax for Ivne10 e100 ex Max. Min. Avg.

a Measuredeb

Lime content 5%Louiseville 2.250 1.480 1.00 1.95 1.79 1.94 1.80St-Alban 1.650 1.120 0.80 1.46 1.35 1.45 1.38Jonquire 2.020 1.370 0.80 1.74 1.59 1.73 1.70Trois-Rivires 0.645 0.560 0.47 0.62 0.61 0.62 0.62Lime content 10%Louiseville 2.250 1.480 1.00 2.54 2.09 2.25 2.60St-Alban 1.650 1.120 0.80 1.83 1.55 1.65 1.47Jonquire 2.020 1.370 0.80 2.30 1.87 2.02 2.00Trois-Rivires 0.645 0.560 0.47 0.66 0.63 0.64 0.67

aValues of Ivn corresponding to the broken line in Fig. 10.bValues ofe obtained by one-dimensional compression test.

Table 3. Calculation ofemax for a desired yield stress of 1000 kPa for lime contents of 5% and 10%.



consider the organic matter content. In addition, the elabora-tion of a design tool for organic soils is very complex be-cause some studies (Montgomery et al. 1991; Tremblay1998; Tremblay et al.2) have shown that the nature of the or-ganic content may also influence the property modifications.

Conclusions

This paper presents the results of a laboratory testing pro-gram for eastern Canadian clayey soils stabilized with ce-menting additives, lime and cement, at high water contents.The main objectives were to establish a general compress-ibility model for treated soils and develop a simple methodto estimate the vertical yield stress of a soil treated with agiven additive content for any initial void ratio. According tothis research, the following conclusions can be made:

(1) A general compressibility model has been developedfor clayey soils from eastern Canada treated with lime or ce-ment which defines relationships between initial void ratio,additive content, and vertical yield stress. The correspondingrelationships provide an estimate of the resistance to com-pression of a specific soil treated with a specific additive at agiven percentage and for any initial void ratio.

(2) The relationships, specific to each tested soil, can benormalized by a modified Burlands (1990) approach usingthe intrinsic compression line of the reconstituted soil. Onthe basis of the tests carried out in this study, the normaliza-tion process allows elaboration of a simple approach to esti-mate the vertical yield stress of inorganic soils treated withlime with any initial void ratio. The only information neededis the one-dimensional compression curve of the reconsti-tuted soil and the void ratio of the soil to be treated.

(3) The normalization in its present form cannot be usedfor organic soil because the effect of the additive is stronglyinfluenced by the organic matter content and by the natureof the organic matter.

(4) These conclusions can be used to estimate the resis-tance to compression of eastern Canadian clayey soils whentreated with lime or cement but should only be used for pre-liminary designs. In fact, this research project has essentiallybeen conducted in the laboratory and no in situ testing hasbeen performed yet to verify the potential of the proposedmethod for in situ conditions.

Acknowledgments

The authors wish to acknowledge the Natural Sciencesand Engineering Research Council of Canada and the Fondspour la formation de chercheurs et laide la recherche duQubec for their financial support, without which this re-search project would not have been possible. The authorsalso thank those who provided technical support in the labo-ratories from the Department of Civil Engineering and theDepartment of Geology and Geological Engineering,Universit Laval, particularly J.-P. Dussault.

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Mechanical improvement and vertical yield stress prediction of clayey soils from eastern Canada treated with lime or cement