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Engineering Geology 53 (1999) 351–358 Swelling–shrinkage properties and soil improvement of compacted expansive soil, Ning-Liang Highway, China Yanjun Du a,*, Shenglin Li b, Shigenori Hayashi c a Faculty of Science and Technology, Graduate School of Science and Engineering, Saga University, Saga 840, Japan b Earth Sciences Department, Nanjing University, Nanjing 210093, People’s Republic of China c Institute of Lowland Technology, Saga University, Saga 840, Japan Received 5 February 1997; accepted 9 December 1998 Abstract In this paper, the swelling–shrinkage properties of the compacted expansive soil in the Huaiyin Section of the Ning- Lian Highway are introduced, and swelling–shrinkage mechanisms are discussed based on changes in soil water content, dry density, material composition and fabric. The improvement of the compacted expansive soil by lime is also discussed briefly. It is concluded that careful attention should be paid to this type of compacted expansive soil. © 1998 Elsevier Science B.V. All rights reserved. Keywords: Expansive soil; Fabric; Soil improvement; Swelling–shrinkage behavior 1. Introduction ignorance of this problem. Thus, in engineering works such as the Ning-Lian Highway (Fig. 1), su cient attention should be paid to this type of Under natural undisturbed conditions, some clayey soils show a certain level of swelling–shrink- expansive soil. age, but their swelling grades are low. When disturbed, compacted and then used for embank- ments and roadbeds, their natural structures are 2. Swelling–shrinkage properties destroyed and cementing bonds broken, the water content decreases, the dry density becomes high In this paper, the investigated expansive soils and the swelling–shrinkage indexes increase. In are alluvial sedimented materials. All are over- this way they may become high swelling grade consolidated. expansive soils. Research has shown that most From Table 1, it can be seen that under natural cracks in embankments and roadbeds are due to undisturbed conditions, swelling–shrinkage indexes of these soils are low except for the yellow * Corresponding author. Present address: Institute of silty soil. Swelling–shrinkage indexes in the paper Lowland Technology, Saga University, Honjo 1, Saga 840-8502, are: swelling pressure, swelling percentage under Japan. Fax: +81-952-28-8189; E-mail address: [email protected] ( Y. Du) 50 kPa and total swelling percentage. Swelling 0013-7952/99/$ – see front matter © 1999 Elsevier Science B.V. All rights reserved. PII: S0013-7952(98)00086-6

Swelling–shrinkage properties and soil improvement of compacted expansive soil, Ning-Liang Highway, China

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Page 1: Swelling–shrinkage properties and soil improvement of compacted expansive soil, Ning-Liang Highway, China

Engineering Geology 53 (1999) 351–358

Swelling–shrinkage properties and soil improvement of compactedexpansive soil, Ning-Liang Highway, China

Yanjun Du a,*, Shenglin Li b, Shigenori Hayashi ca Faculty of Science and Technology, Graduate School of Science and Engineering, Saga University, Saga 840, Japan

b Earth Sciences Department, Nanjing University, Nanjing 210093, People’s Republic of Chinac Institute of Lowland Technology, Saga University, Saga 840, Japan

Received 5 February 1997; accepted 9 December 1998

Abstract

In this paper, the swelling–shrinkage properties of the compacted expansive soil in the Huaiyin Section of the Ning-Lian Highway are introduced, and swelling–shrinkage mechanisms are discussed based on changes in soil watercontent, dry density, material composition and fabric. The improvement of the compacted expansive soil by lime isalso discussed briefly. It is concluded that careful attention should be paid to this type of compacted expansive soil.© 1998 Elsevier Science B.V. All rights reserved.

Keywords: Expansive soil; Fabric; Soil improvement; Swelling–shrinkage behavior

1. Introduction ignorance of this problem. Thus, in engineeringworks such as the Ning-Lian Highway (Fig. 1),sufficient attention should be paid to this type ofUnder natural undisturbed conditions, some

clayey soils show a certain level of swelling–shrink- expansive soil.age, but their swelling grades are low. Whendisturbed, compacted and then used for embank-ments and roadbeds, their natural structures are

2. Swelling–shrinkage propertiesdestroyed and cementing bonds broken, the watercontent decreases, the dry density becomes high

In this paper, the investigated expansive soilsand the swelling–shrinkage indexes increase. Inare alluvial sedimented materials. All are over-this way they may become high swelling gradeconsolidated.expansive soils. Research has shown that most

From Table 1, it can be seen that under naturalcracks in embankments and roadbeds are due toundisturbed conditions, swelling–shrinkageindexes of these soils are low except for the yellow

* Corresponding author. Present address: Institute ofsilty soil. Swelling–shrinkage indexes in the paperLowland Technology, Saga University, Honjo 1, Saga 840-8502,are: swelling pressure, swelling percentage underJapan. Fax: +81-952-28-8189;

E-mail address: [email protected] (Y. Du) 50 kPa and total swelling percentage. Swelling

0013-7952/99/$ – see front matter © 1999 Elsevier Science B.V. All rights reserved.PII: S0013-7952 ( 98 ) 00086-6

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352 Y. Du et al. / Engineering Geology 53 (1999) 351–358

Fig. 1. A sketch of highway construction in Jiangsu Province.

pressure is measured using an oedometer, under yellow silty soil remains non-expansive, even afterremolding and compaction. Another indication is100% saturation of the soil specimen. The swelling

percentage under 50 kPa (dep50) is also measured that the swelling percentage under 50 kPa of undis-turbed soil is below zero, and increases above zerousing an oedometer with 50 kPa vertical pressure

load on soil specimens under 100% saturation. The (except for the yellow silty soil ) after being com-pacted. The increasing rate is of the same order astotal swelling percentage (dps) is calculated as:

dps=dep50+ls(w−ws), in which ls is the soil shrink- that of the swelling pressure. The total swellingpercentage (dps) is a complex index which wellage coefficient, ws is the shrinkage limit, and w is

the natural water content. The swelling indexes describes the swelling–shrinkage properties of soil.dps of the undisturbed soils becomes relativelybecome high for remolded and compacted speci-

mens (Table 1). For example, the swelling pressure higher after being compacted, dps of the grey soilbeing the largest. It increases nearly three times,of a type of soil named grey soil increases by 27

times, varying from 22 kPa to 587 kPa, while that from 4.3% to 11.8%, and that of yellow silty soilis the lowest. According to Li et al. (1992), soilsof so-called black soil increases by 38 times, rang-

ing from 10.1 kPa to 385 kPa. The swelling pres- with dps greater than 0.7% should be consideredas expansive. So these compacted soils are expan-sure of greyish-yellow soil increase by about seven

times, changing from 40 kPa to 276 kPa. Only the sive soils, excluding the yellow silty one.

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353Y. Du et al. / Engineering Geology 53 (1999) 351–358

Table 1Comparison of swelling–shrinkage indexes between compacted and undisturbed soils

Index Soil type Undisturbed soil Compacted soil U/C

Swelling pressure (kPa) grey soil 22 587 27black soil 10.1 385 38greyish-yellow soil 40 276 7yellow silty soil 6 7.5 1

dep50 (%) grey soil −0.7 11.8black soil −1.9 7.3greyish-yellow soil −1.2 5.5yellow silty soil −3.7 −0.5

dps (%) grey soil 4.3 11.8 3.0black soil 7.3 7.5 1.0greyish-yellow soil 2.9 6.2 2.0yellow silty soil −0.7 −0.4 1.0

Swelling–shrinkage classification grey soil moderate highblack soil high highgreyish-yellow soil low highyellow silty soil non non

dep50=swelling percentage under 50 kPa; dps=total swelling percentage; U=undisturbed soil; C=compacted soil.

3. Mechanisms soil increases also. This phenomenon varies depend-ing on the conditions of dry density and watercontent. For example, for a specimen with low3.1. Change in dry density and water contentwater content, the formation of a moisture film iseasy and it reaches maximum thickness in a shortFrom Table 2, it can be seen that dry densities

of undisturbed soils are larger while water contents time. However, when the dry density is high, thereare more clay particles per volume of soil (this isare lower compared with compacted soils. The

change in dry density and water content is a direct of benefit to the swelling), and thus the reactionsbetween particles and water are more important.reason for the different swelling–shrinkage proper-

ties between compacted soils and undisturbed soils. The dry densities of compacted soils in Table 2 arehigher and their water contents are lower. On theThe swelling of soil is due to a moisture film

forming around the particles as a result of reaction contrary, undisturbed soils show no such perfor-mance. Thus it is clear that the degree of waterbetween the clay particles and water. As the thick-

ness of moisture film increases, the volume of the saturation plays an important role in soil swelling.

Table 2Comparison of dry density and water content between compacted and undisturbed soils

Soil type Dry density (g/cm3) Water content (%)

Undisturbed soil Compacted soil Undisturbed soil Compacted soil

grey soil 1.33 1.74 34.2 19.5black soil 1.30 1.60 43.9 24.5greyish-yellow soil 1.54 1.71 27.4 20.0yellow silty soil 1.55 1.63 25.8 14.2

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354 Y. Du et al. / Engineering Geology 53 (1999) 351–358

3.2. Material composition cated natural events, undisturbed soil mass devel-ops a certain structural strength, and strongconnections form among soil particles. This canIt is not the case that all soils become ‘artificially

expansive’ after remolding and compaction. Only partly suppress the swelling. On the contrary, inlaboratory compacted soil which has been ground,those which have hydrophilic clay mineral and

clay particle contents close to those of expansive remolded and compacted, its original structure isdestroyed, the natural structural strength is low-soils may change to ‘artificially expansive’ after

compaction. All the soils shown in Table 3 have ered, and thus factors suppressing swelling areremoved, making swelling easier. Table 4, whichhigh illite contents, but illite–smectite mixed-layer

mineral percentages are high only in grey soil and well describes the fabric differences between com-pacted soils and undisturbed soils, can explain thegreyish-yellow soil. Meanwhile, both smectite and

illite are hydrophilic clay minerals, so the swelling phenomenon quite clearly. To get the scanningelectronic microscope (SEM) photographs, all theabilities of compacted grey soil and greyish-yellow

soil are high. Besides, the clay particle content also specimens were prepared by the freeze-dry methodusing a freeze–vacuum sublimation desiccator. Inhas an important influence on compacted soil

properties. Though yellow silty soil is composed this way, specimens can meet the microscopic testrequirements. Details of the device are discussedmainly of illite, it contains only 2.8% of clay

particles. Therefore, its properties vary little after by Li et al. (1992).From Table 4 and Figs. 2–7, it can be seen,compaction. Tahir (1992) also indicated that clay

particle content has an influence not only on the except for yellow silty soil, that the fabrics ofundisturbed soils have changed after compaction.change in dry density but also on the features of

the soil fabric. The fabrics of compacted soils are mainly ofturbulent or turbulent-orientation aspects (Osipov,1979), their pores distribute homogeneously and3.3. Change in fabricform rows of channels (Fig. 2). When soil isimmersed in water, water can penetrate easilyUndisturbed soil is the result of its geological

and stress/strain history. After long and compli- along these channels, which makes aggregated

Table 3Material composition of soils

Soil type Clay mineral composition (%) Clay particle content (%)

I I–Sm Ch

grey soil 56 19 9 51.9black soil 58 trace 19 56.1greyish-yellow soil 39 35 20 50.3yellow silty soil 62 trace 20 2.8

I=illite; I–Sm=illite and smectite mixed-layer mineral; Ch=chlorite.

Table 4Comparison of fabrics between compacted and undisturbed soils

Soil type Undisturbed soil Compacted soil

grey soil turbulent fabric turbulent-orientation fabricblack soil aggregate fabric turbulent-orientation fabricgreyish-yellow soil matrix fabric (Osipov, 1979) turbulent fabricyellow silty soil aggregate-skeletal fabric aggregate-skeletal fabric

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Fig. 2. SEM photograph of grey undisturbed soil. Fig. 5. SEM photograph of black compacted soil.

Fig. 6. SEM photograph of greyish-yellow undisturbed soil.Fig. 3. SEM photograph of grey compacted soil.

Fig. 7. SEM photograph of greyish-yellow compacted soil.Fig. 4. SEM photograph of black undisturbed soil.

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356 Y. Du et al. / Engineering Geology 53 (1999) 351–358

Table 5Variation of swelling–shrinkage indexes and unconfined compression strength of compacted soils before and after lime treatment

Swelling indexes Soil type Pre-treatment Post-treatment

Swelling pressure (kPa) grey soil 587 30black soil 385 134greyish-yellow soil 276 37yellow silty soil 7.5 10

dep50 (%) grey soil 11.8 −0.4black soil 7.3 0.3greyish-yellow soil 5.5 −0.3yellow silty soil −0.5 −0.5

dps (%) grey soil 11.8 −0.4black soil 7.5 1.25greyish-yellow soil 6.2 −0.4yellow silty soil −0.4 −0.2

Unconfined compression strength (kPa) grey soil collapse 893(after seven days soaking in water) black soil collapse 423

greyish-yellow soil collapse 1191yellow silty soil collapse 101

Swelling–shrinkage classification grey soil high nonblack soil high lowgreyish-yellow soil high nonyellow silty soil non non

dep50=swelling percentage under 50 kPa; dps=total swelling percentage.

Fig. 8. Comparison of total swelling percentage between pre- and post-time treatment of compacted expansive soils (44 – grey soil;64 – black soil; 132 – greyish-yellow soil; 80 – yellow silty soil ).

particles react with water sufficiently. As for the difficulty. The comparison of the fabrics betweencompacted soils and undisturbed soils well explainsfabrics of undisturbed soils, most of the pores are

micro ones and they do not distribute homoge- this point due to ‘osmotic’ swelling. Furthermore,the presence of illite can influence the behavior,neously. So water penetrates into the soil with

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357Y. Du et al. / Engineering Geology 53 (1999) 351–358

Fig. 9. Comparison of swelling pressure between pre- and post-treatment of compacted expansive soils (44 – grey soil; 64 – blacksoil; 132 – greyish-yellow soil; 80 – yellow silty soil ).

by water intake into the interlayer space between is relatively poorer, with its swelling pressure drop-particles. The fabric of yellow silty soil does not ping to 134 kPa, and its total swelling percentagevary obviously prior to and after compaction, the dropping to 1.25%. This soil therefore still belongssize of structural elements does not change much to the category of expansive soil. The reason foreither, the dry density and structure connection this may be that the organic matter content of theforces of undisturbed soil are close to those of black soil is 1.5%, which is as much as seven timescompacted soil. Therefore, the swelling–shrinkage that of the grey soil. Among the soils, the improve-properties do not differ much. ment result of the yellow silty soil is the poorest.

We were not able to evaluate the role of organic With sufficient reaction between the compactedmatter in the soil fabric during this project. expansive soil and the lime, a change in the

exchange cation causes the aggregation of the clayparticles, the appearance of cemented fine needle

4. Soil improvement lime among the clay particles, and a change in soilfabric is also observed (Li et al., 1992). The fabric

To reduce the swelling, 8 wt.% lime was added becomes more dense compared with the untreatedto the compacted expansive soil specimens and

compacted expansive soil. This is also shown byhomogeneously mixed. 24 h under laboratory con-

SEM photographs. The physical and mechanicalditions were allowed to pass for sufficient reactionproperties of the compacted expansive soil arebetween the lime and the expansive soil specimen.therefore improved.The water content of the mixture was allowed to

reach an optimum and, to carry out the swellingtest, the dry density of the specimen was alsopermitted to reach a maximum. For the unconfinedcompression strength test after seven days soaking

5. Conclusionin water, each specimen was formed into a4×5 cm2 cylinder.

The breakdown of the cementing bonds and theFrom Table 5 and Figs. 8 and 9, it is clear thatchange in the fabric are the main factors affectingthe improvement in the grey soil is the best, withthe change in swelling ability and pressure of theits swelling pressure dropping to 33 kPa, its totalcompacted expansive soil. Careful attention shouldswelling percentage dropping to −0.4%, and thebe paid to such soils in engineering works.unconfined compression strength increasing from

0 to 893 kPa. The improvement in the black soil Improvement by lime ameliorates swelling damage.

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Osipov, V.I., 1979. Nature of Strength and Deformation Prop-Referenceserties of Clayey Soils and Rocks. Moscow University Pub-lishing House, pp. 58–102 (in Russian).Li, S. et al., 1992. Study on the Engineering Geology of Expan-

sive Soils in China. Jiangsu Science and Technology Publish- Tahir, A.A., 1992. Collapse mechanisms of low cohesion com-pacted soils. Bull. Assoc. Eng. Geol. 4, 345–353.ing House, pp. 129–140.