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Soil compaction at low moisturecontent-field trials in Sudan

C I Ellis

Overseas CentreTransport Research LaboratoryCrowthorneBerkshire RG45 6AUUnited Kingdom PAI 1O0/ 1O

PAI 10 1/80 ELLIS, C I (1980). Soil compaction at low moisture content - field trials in Sudan.7th Regional Conference for Africa on Soil Mechanics and Foundation Engineering, Accra, Ghana,1- 7 June 1980

Seventh Regional Conference for Africa on Soil Mechanics and Foundation Engineering /Accra /June 1980

Soil compaction at low moisture content

Field trials in Sudan

C.1. ELLIS

Transport & Road Research Laboratory, Crowthorne, Berks., UK

SYNOPSIS. The difficulty of achieving optimum moisture content for the compaction of'soils in arid areas is outlined, and past experience in soil compaction at low moisturecontents is reviewed. The construction of a trial road embankment of' a black siltyclay in Sudan is described. The plasticity index of the fill material was 26-36 and itwas compacted at its field moisture content, 20 per cent less than the Proctor optimummoisture content. Two types of rollers were used and densities ranging from 94 to 105per cent of Proctor maximum dry density were achieved. In spite of the low moisturecontent at which it was compacted, this embankment has performed satisfactorily for ayear and a half and the road it carries has suffered no ill effects. The implicationsare examined of using dry compaction for road construction on expansive clays in aridareas.

RESUME. Le rapport d~crit la difficult4 d'obtenir une teneur en eau optimale pour lecompactage des sols et passe en revue les experiences d6.j~. faites en matibre' decompactage des sols h teneurs en eau basses. La construction d'un remblai experimentalpour route en argile de limon noire, au Soudan, est d~crite. L'indice de plasticit6du rnat~riau de remblai 6tait de 26-36 et le compactage ava~it 6t effectu6 a. la teneuren eau in situ, c'est a. dire h 20 pour cent de momns que la teneur en eau optimale deProctor. Deux types de rouleaux ont ~t6 utilis6s, gr~ce auxquels on a atteint desdensit~s allant de 94 ~L 105 pour. cent de la densit6 s~che maximale Proctor. En d~pitde la teneur en eau basse, a laquelle le compactage a 6t6 effectu6, la performance duremnblai s'est av~r~e satisfaisante pendant un an et demi et la route sur le remblai n'asouffert aucun effet nocif'. L tauteur examine les implications pour la constructionrouti~re du compactage a. sec des argiles expansives dans les zones arides.

1. INTRODUCTION

Traditionally, the student of' compaction-is taught that good construction practicerequires unbound road materials and soilsto be compacted at their optimum moisturecontent as determined in a suitablelaboratory compaction test so that maximumdensity can be achieved with a givencompactive effort. Where materials occurnaturally at moisture contents close tothis optimum value, or where water ischeaply available, this requirementpresents few problems. However in aridareas water can be an expensive con-struction material, and in addition themixing of' large quantities of' water intofine grained soils can present severetechnical problems. Thus there are

considerable economies available if' it canbe shown that adequate performance can beassured when materials are compacted with-out the addition of' water, or with theaddition of' only a small amount.

2. DRY COMPACTION

Standard laboratory compaction tests giverelationships of' the type shown in Fig. 1.For a particular compactive effort in-creasing moisture contents yieldincreasing densities up to the optimummoisture content, but beyond this pointthe addition of' further water leads tolower densities. As the compactiveeffort increases the dry density increases,but the optimum moisture content is re-duced. Similarly with field compac~tion

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\ Zero air voids

Higher compactive effort

Lower compactive effort

0

I II Optimum

I moisture

11 1 content

Moisture content

Fig. 1 Conventional compaction curves

plant on the same soil the heaviest rollerscompact most effectively at lower moisturecontents than the lighter rollers.If compaction tests are carried out

using a larger number of test points anda range of moisture contents extendingtowards zero, the resulting compactioncurve can be irregular such as thatindicated in Figure 2. The exact form ofthe curve depends on the type of thematerial, but it is not uncommon for theextended compaction curve to have aminimum value and a portion where densitydecreases as the moisture content isincreased. Many examples of extendedirregular compaction curves are reportedin the literature (Morris 1975, Graceand Cocksedge 1.978, Lee and Suedkamp1972, Lee 1976, Lewis 19514, Lewis andParsons 1961, Mtango.1979, Forssblad1974). The shape of this 'dry end' of thecompaction curve is particularly relevantto any study of 'dry' compaction. In theexample of Fig. 2 there are certain~values of dry density which can beachieved at three different moisturecontents with the same compactive effort.It is necessary to know whether compactionat the driest moisture content is feasiblein practice and how many materials havecompaction curves with this feature.

Moisture content

Fig. 2 Extended irregular compaction curve

Compaction is normally measured in termsof the dry density of the material. Whilstthis is undoubtedly the most importantparameter, there are other factors whichneed to be considered. High air voidscontents and high soil suction valuesboth have a potential for causing problemsafter construction, and the lack of cohesionin dry materials can cause severe con-struction difficulties.

3. AVAILABLE EXPERIENCE

3.1 Australia

A considerable amount of research on com-paction was carried out during the years1962-73 on a wide range of roller typesand materials. The studies covered awide range of moisture contents. A numberof authors were concerned with this work,but a summary was prepared by theAustralian bad Research Board as ARBBReport No. 3~ (Morris 1975).

In current construction practiceattention is paid to the scheduling ofconstruction work such that dams may bebuilt or bores drilled several seasonsin advance of the work so that compactionwater is available when required. Inaddition care is taken to make the bestuse of water by applying it at the timeof day when it will have most effect eg

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t

07

Zero air voids

---------7

at night or early morning when evaporationrates are low. Heavy rollers are normallyemployed in order to take advantage oftheir lower roller optimum moisture con-tents. Dry compaction of sub-grades isnot uncommon in arid areas but pavementmaterials are normally compacted at ornear roller optimum moisture content.In areas of expansive clays attempts aremade to compact at the estimated ultimateequilibrium moisture content in order tominimise subsequent volume changes andconsequent cracking.

3.2 South Africa

About 13 years ago the University ofPretoria completed a three part study ofsoil compaction in arid areas (Van Rooyenand Wessels 1967 a, b, c) which concen-trated largely on the use of additives toassist compaction. This study was followedby a report on the uses of additives byNIRR (Todres 1970). Additives which aresurface-active agents lower the surfacetension of water and hence cause it to wetsurfaces more effectively. The additionof these substances therefore improvesthe wetting of soil particles and improvesthe interparticle lubrication in thecompaction process. Other additivescreate a flocculant effect whereby longchain molecules with two ionic groupslatch onto soil particles and pull themtogether. In each case the overall effectis to lower the optimum moisture contentfor a particular level of compactionwithout significantly affecting themaximum dry density.

The development of the impact roller inSouth Africa was originally geared to thecompaction of 'collapsing' soils but theroller has since been found to provideeffective compaction to depths of 2 to 14metres in uniform sands at low moisturecontents (Clifford 1976).

3.3 North Africa

Trials carried out in Algeria (RepublicAlgelienne Democratique et Populaire 1977)on sands and gravels suggested that theseparticular materials were difficult touse for a dry compacted road. Tests inMorocco (Kabbaj 1979) using natural wellgraded gravels as fill material werereported to be successful but problemswere experienced with dry sands.

Farther south in Mali, experiments withdry compaction on gravel roads arereported to have been particularlysuccessful and the technique is now being

used in other countries involved with theUNDP Sahelian feeder road project(International Road Federation 1978).

3.4 Europe

In the past a great deal of compactionresearch has been carried out in theUnited Kingdom by TRRL and in France byLCPC but naturally very little of it hasbeen directly relevant to problems ofdry compaction in arid areas. At TRRLearly work (Lewis 19514) included testswith fairly low moisture contents butonly recently has a research programmebeen started to look specifically at aridarea construction techniques. Elsewhereinvestigations have been carried out intothe dry compaction of sand (Grace andCocksedge 1978). French work on crushedquartzite sands is of particular interestto students of dry compaction (Chaigneand Blivet 1971). The highest densitieswere achieved at zero moisture contentand good results, were obtained from a widerange of vibrating rollers.

More recently the Norwegian RoadResearch Laboratory have studied the drycompaction of a Kenyan gravel (Mtango1979) and concluded that with thismaterial successful dry compaction wasonly likely when natural moisture con-tents were very close to zero.

Most of the practical research on drycompaction carried out to date has beenconcerned with sand and gravel materials.Clearly many materials in this broadcategory can be compacted adequately with-out added water and give good road per-formance. However it is not clear whatcriteria should be adopted in the selectionof materials or compaction techniques toensure adequate performance. Dry com-paction is not usually attempted forpavement materials on surfaced roads.

Published work on dry compaction ofclays is virtually limited to theAustralian experience where the mainrecommendation for expansive materialsis to compact at moisture contents closeto 'equilibrium'

For all materials, vibrating rollersare generally favoured as the mosteffective type of plant for dry compaction.

4. DRY COMPACTION TRIAL TN SUDAN

14.1 Design of experiment and laboratorytesting

A full-scale compaction trial has been

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undertaken by TRRL in collaboration withthe Sudanese Roads and Bridges PublicCorporation. The trial, which was con-structed in May/June 1978 on the WadMedani-Sennar-Kosti road project, wasdesigned to study the dry compaction ofa black silty clay' for use on a roadembankment and subgrade. The experimentalsite is approximately 27 kilometres westof Sennar in' an area where the averageannual rainfall is 1400-500 mm, all con-centrated in the months June to September.

The expansive silty clay contains about87 per cent of material passing the 75 p.msieve, is derived from igneous rocks, andcontains clay minerals of the montmorillon-ite type. It is classified as NH on theCasagrade classification system with aLiquid Limit of 64-76 per cent, PlasticLimit of 38-142 per cent and a PlasticIndex of 26-36 per cent.

At the trial site minor alterations tothe vertical'alignment of the road wereapproved in order that a standard embank-ment height of 1.2 metres could be main-tained over the whole trial length. Theexperiment occupied a total length of 600metres and was divided into 6 trialsections of 100 metres each (see Figure 3).It was decided that all sections would beconstructed in 6 equal layers of 200 mmcompacted thickness, and that the onlyvariables would be the moisture contentof the fill material and the type ofroller. The moisture content for aparticular section was controlled by

200

400

600

-E

0

800

1000

1200

1400

1600

1800

2000

0 2 4 6

Moisture content (per cent)

8 10 12 14 16 18 20 22 24

Fig. 4 Moisture content profile in natural ground - May 1978

permitting scrapers to excavate materialonly from between given depths in theborrow area. Hence with the soil moistureprofile shown in Figure 14 material excava-ted from the surface to 300 mm had amoisture content range of 7-11 per cent;material from 300 mm to 600 mm had a rangeof 11-14 per cent; and material from below600 mm had a moisture content greater than14 per cent.

Single surface dressing

Lime stabilised gravel base - 150mm

200 mm

Subgrade 200 mm

fill 200mm

total 200mm

1.2m 200mm

200mm

Compaction

27

Gravel sub-base layer No. 2 - 150 mm

Gravel sub-base layer No. 1 - 1 50mm

Moisture Moisture Moisture Moisture Moisture Moisturecontent content content content content content

> 14% 7- 11% 7 -11% 11 -14% 11 -14% 1 1-~14%

Pneumatic Vibrating Pneumatic Vibrating Pneumatic Pneumatictyred roller roller tyred roller roller tyred roller tyred roller

Section A Section B Section C Section D Section E Section F

+000 27+100 27+200 27+300 27+400 27+500 27+600

Fig. 3 Dry compaction trial: Sennar - Kosti road

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The selection of rollers was limited tothe two ty-pes of' roller in common use onthe project. One was a 10-tonne selfpropelled vibratory roller (AvelingBarford VS Vibra Victa), and the otherwas a 8 -tonne pneumatic tyred roller(Aveling Barford PM20) which when fullyballasted operated at nearly 20 tonnes.

.The five, sections A, B, C, D and E wereall covered with a pavement similar tothat used elsewhere on the main project.This comprised two 150 rm sub-base layersof natural gravel, 150 mm layer of limestabilised gravel base, a prime coat anda single surface dressing. The onlydifference between the pavement over thetrial sections and the main projectpavement was the substitution of a singlesurface dressing for the 50 mm asphalticconcrete surfacing. Section F only, hada pavement of one layer of natural gravelsub-base. It was intended that anysubsequent settlement as a result of thedry compaction should be substantiallyover before the rest of the pavement wascompleted.

Laboratory compaction tests were carriedout at different levels of compaction andyeilded the relationships shown inFigure 5. For the ordinary BS compactiontest (British Standards Institution, 1975)the optimum moisture content was 29.5 percent with a maximum dry density of 1.45mg/rn3 (90.7 lb/ft3) compared with HeavyBS values of 22.3 per cent for optimummoisture content and 1.70 Mg/in3 (106.2lb/f't3) for maximum dry density. Aspreviously mentioned the irregular shapedcompaction curves such as those shown inFigure 5 are particularly significant forthe study of dry compaction. Althoughthese curve shapes are not uncommon whencompaction testing is extended to includevery dry materials, many engineers arenot familiar with this type of relation-ship. This is because normal compactiontest procedure is only concerned withvalues close to the conventional optimummoisture content.

The laboratory compaction testing wascarried out in 6 in. diameter moulds sothat each specimen could be used for CBRtesting also. Figure 6 gives the Iso-CBRchart which provides an indication of thesensitivity of the soil strength tomoisture content and density.

M.

E

C

Q

1.7

1.6

1.5

105

100

95

C

Q

90

85

800 10 20 30

Moisture content (per cent)

Fig. 5 Comparison of field and laboratory compaction

1.4

0.3 L.

1.7

1.6 F-

C.,

E

C

0

1.5 I-

105

100

C

0

90

1.4 [-

1.3 I

85

I C...(per cent)8 1 Compaction

- I- I I0 10 20 30

Moisture content (per cent)

Fig. 6 ISO-CBR Chart - Laboratory compaction

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4.2 Construction

The first construction operation was toinstall concrete monuments on each sideof the road to mark the precise chainagesof the beginning and end of each trialsection and to act as temporary bench marks.Because of the expansive nature of theblack silty clay these monuments were notadequate as permanent bench marks andtherefore a suitable bench mark wasinstalled on an adjacent 'Jebel' (rockoutcrop).

The new road embankment was to bebuilt on the line of the existing trackbut before construction started the wholearea was cleared of vegetation and agrader used to carry out minor earthmovingoperations. This operation was requiredso that the height of fill material wouldbe identical for all six trial sections.

Apart from the moisture content of thefill material and the type of roller usedfor compaction, the construction andtesting procedure was identical for eachlayer and each section. Fill materialwas excavated with scrapers from theappropriate depths in the borrow pit toensure uniform moisture content and thentransported and spread on the trialsection. The loose material was shapedwith a grader and levels checked beforebeing rolled with 12 passes of theappropriate roller. Measurements werethen made of dry density, moisture con-tent and Impact Value (Clegg 1977) andoptical levels were taken to provide crosssection details.

Dry density measurements were made atsix points per layer for each sectionusing the sand replacement method.Average values were between 94 and 105per cent of BS comapaction test maximumand it is particularly significant thatfor both rollers the field densityvalues decrease as the moisture contentincreases over the range of moisturecontents studied. Because of the drymaterial there was considerable difficultyin making regular shaped density holesand this almost certainly contributed tofairly wide variations in the measureddensities. The differences between thetwo rollers were not significant andtherefore a single line is drawn torepresent all field compaction (Figure 5).The field density results over this

limited range of moisture contentssuggests that the field compaction curveshave a similar shape to the laboratorycompaction curves in as much as that theyhave a marked minimum density value.

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Since field moisture conditions, in thiscase at least, are on the dry side of themoisture content corresponding to the min-imum density it seems likely that somenormal field compaction operations wouldpermit the adding of insufficient water toreach the conventional optimum. Thiscould encourage compaction to be carriedout at or near the moisture contentcorresponding to the minimum dry density.In view of the known practical difficultiesin adding and mixing large quantities ofwater particularly to clay soils, itappears in some cases that much of theeffort employed in hauling water in aridareas could be counter productive inachieving high densities. Certainly thesubject requires some detailed considera-tion before large compaction programmesare undertaken in arid areas.

Moisture contents and Impact Values wertboth measured at twenty points per layerfor each trial section. The means of alltest values for each trial section aregiven in Table 1.

On completion of the trial embankmentthe pavement layers were constructed inthe same way as elsewhere on the WadMedani-Sennar-Kosti project. No attemptwas made to use dry compaction but con-struction quality was monitored in asimilar way to the experimental sections.On completion of the surface dressing andopening to traffic, cross section levelswere taken at 0.5 metre intervals acrossthe road to provide a datum for comparisonwith subsequent levels.

~4.3 Performance

The construction of the experimentalsections was completed just before the1978 wet season. Since that time therehave been three detailed inspections ofthe road at which a visual assessment wasmade of the road condition together witha traffic survey and determination ofcross section levels and moisture con-ditions in the embankment.

Moisture conditions were monitored bydigging a hole through the pavement to thesub-grade and then augering to a depth ofabout 1 metre taking samples at 300 mmintervals. This operation was repeated 3times at a selected chainage within eachtrial section such as to give values be-neath the centre line and under each edgeof the pavement. The selected chainagewas different for each inspection. Themoisture content profiles and theirchanges with time are indicated in Figure7. These measurements have given no causefor concern for the performance of thetrial sections.

Table 1. Mean test values - embankment.

Section Section Section Section Section SectionA B c D E F

Dry density Mg/rn 1.35 1.148 1.49 1.140 1.37 1.35lb/ft3 814.53 92.55 93.36 87.149 85.36 814.49

Moisture content - 114.9 8.73 8.67 12.86 13.19 13.88per centImpact Value132 1. 116 1.1.121(Clegg 1977)132 l6 116 18 12121

Analysis of the cross section levelssuggest that there has been negligibledifferential settlement since the com-'pletion of construction and there is nodeterioration of the road surface shapewhich can be attributed to any effect ofthe dry compaction procedures adoptedduring construction.

The visual assessments carried out ateach inspection have yielded only minorsigns of road deterioration. At thefirst inspection only one small crack wasidentified. At the second inspection afew additional cracks had appeared butthey were sealed with hot bitumen andchippings. At the third inspection nofurther cracks could be identified. Thenature of the cracks suggest that theywere related to the stabilised baserather than the dry compaction of thesubgrade and fill materials. At theedge of the embankment there areoccasional erosion channels which needto be rectified before the next wetseason.

Traffic counts made since the completionof construction suggest that in the dryseason the average daily traffic is about200 vehicles in both directions but fall-ing to about 100 vehicles per day in thewet season. No doubt this fluctuation willeven out once an all-weather route iscompleted to Kosti. Commercial vehiclesform about 80 per cent of the totaltraffic.

14.14 Conclusions from Sudan experiment

From the results of the experiment so farit appears that compaction of clayembankments without added water may bea perfectly acceptable constructiontechnique for use in this part of Sudan.However the satisfactory performance ofthese trial sections only proves thatdry compaction is effective under theparticular conditions of the experimentand further investigations are requiredinto the sensitivity of road performanceto different levels of supervision or

variations in thickness of compactedlayers, number of roller passes andmaterial characteristics.

Field dry density values of between 914and 105 per cent of BS maximum dry densitywere generally higher than expected, butin part this may have been due to theexpansive nature of the soil in that theshrinkage of the material at low moisturecontents makes it easier to pack morematerial into a given volume.

The differences in performance betweenthe pneumatic tyred roller and thevibrating smooth wheel roller were neg-ligible under the conditions 'of thistrial. This does not necessarily meanthat both rollers are equally efficient.One roller may be capable of achievingthe final density with a smaller numberof passes than the other. It is alsopossible that one roller was moreeffective at producing additional com-paction at depths below the top layer.Such an effect would not have beenidentified by-the density testing procedureadopted during this trial. However manyengineers would expect the vibrating rollerto be more effective than the pneumatictyred roller in both these respects.

In most situations dry density is themost important parameter in assessing theperformance of dry compaction. Howeverin dry conditions high densities will alsobe associated with high air voids andthese could lead to problems if theembankment wetted up too quickly. Themoisture measurements made during thistrial gave no indication that soil moisturechanges are creating any problems.

5. IMPLICATIONS FOR ROAD CONSTRUCTION ONEXPANSIVE CLAYS IN ARID AREAS.

5.1 Subgrade strength

Because the relationship between moisturecontent and suction exhibits hysteresisbetween the wetting and drying curves, itcan be shown that a dry compacted subgradewill attain a lower equilibrium moisture

337

- . Mean moisture content for Section at construction May 1978

- -- Mean moisture contents October 1978- - Mean moisture contents March 1979

Mean moisture contents September 1979

Top ofsubgrade

Section FGravel

Layer6 I

Layer 5 rrLayer 4 _ _ 4Layer 3

Layer 2

Layer 1

9 12 15 18 21

Top of Section Fsubgrade Gravel

Layer 6

LayerS I

Layer 4

Layer 3 i

Layer 2

Layer 1

Depth(mm)

200

400

600

800

1000

1200

9 1 2 1 5 18 21 9 12 15 18 21 9 12 15 18 21

Moisture content (per cent)

(a) Moisture contents under centre line

Depth(mm)

200

400

.600

800

1000

1200

9 12 1 5 18 21 9 12 1 5 18 21 9 12 1 5 18 21 9 12 15 18 21

Moisture content (per cent)

(b) Moisture contents under pavement edge

Fig. 7 Changes in moisture content since construction

338

1

content than one that has been compactedat a moisture content wetter than theultimate equilibrium value. This lowermoisture content results in higher :sub-grade strength and hence increases thelife of the road. In addition thegreater stiffness of the stronger subgradesprovides' a better platform for the com-paction of subsequent layers thus helpingto obtain the best possible performancefrom the pavement. Alternatively it canbe argued that thinner pavements arerequired for the same performance.Although not related specifically to thequestion of dry compaction of expansiveclay fills, the principles relating tothe prediction of the strength of clayfill subgrades and its relation to roadperformance have been discussed by Blackand Lister (Black and Lister 1978).

5.2 Volume changes and cracking

Wet expansive clay will shrink and crackwhen the moisture content is reduce dcausing cracks to appear in the roadpavement above. These cracks subsequentlypermit water to enter the structure andcreate a weakness which eventually causescomplete road failure. This failuremechanism is only too familiar to highwayengineers and others working with expan-sive clays. Dry compaction is one way inwhich the adverse effects of expansiveclays can be minimised since materialscompacted dry may be expected to graduallywet up to equilibrium moisture contentwithout cracking. In the absence ofcracking subsequent wet and dry cycleswill have a minimum effect on a roadpavement. If compaction is carried outat the equilibrium moisture condition thenin theory there should be no cracking andno volume change.

5.3 Differential swelling and settlement

When water is added to clay materialsit is very difficult to obtain goodmixing and even distribution of moisture.This means that different parts of thesoil mass will expand or shrink bydifferent degrees as equilibrium valuesare approached and potentially this cancause differential movements and possiblycracking in the road pavement. Howeverat naturally occurring moisture contentsthe distribution of water throughout thematerial is very even and thereforechanges in moisture content towardsequilibrium values are more likely to beaccompanied by uniform movements withinthe soil mass, thus reducing the chancesof pavement deformation and cracking.

5.4 Collapse settlements

The size distribution of individualfragments or clods of dry clay will un-doubtedly affect the compaction andperformance characteristics of a claymaterial. Depending on the plasticity,the clods will have different resistanceto the breaking down action of constructionplant. Dry compacted clays will usuallyhave high air voids which could permitmoisture changes to take place quiterapidly. The points of contact betweenthe dry clay fragments or clods are highlystressed and the addition of water mayallow softening at the points of contactwith consequent collapse settlement.

5.5 Compacted densities

Laboratory compaction trials do notnecessarily give the same relationshipsbetween density and moisture content asfield compaction and therefore it isimportant to select the laboratory tes twhich best reproduces field conditions.Where the use of dry compaction isanticipated laboratory vibrating hammerdensity tests should be considered inaddition to the normal falling hammertests.

If the natural moisture content is lessthan that corresponding to any minimumdensity value on the relevant compactioncurve, adding water in insufficientquantities may lead to compacted densitieslower than could be obtained withoutadded water.

The factors discussed above considersome of the main implications of adoptingdry compaction of expansive clays in aridareas. Compared with traditional com-paction methods at optimum moisturecontent, dry compaction offers thepossibility of increased subgrade strength,reduced cracking, reduced differentialmovements and reduced costs. Drydensities are likely to be lower than thoseto be expected at optimum conditions butpossibly higher than those often achievedin practice. It is essential thatrealistic relationsh'ips between density,moisture content and compactive effortare derived for each new material beforedry compaction is attempted on a majorproject.

The major disadvantages relating to drycompaction appear to be related to thehigh air voids and the risks of collapsesettlement.

6. ACKNOWLEDGEMENTS

The author wishes to thank the Roads and

339

Bridges Public Corporation, Sudan andparticularly El Amin Hussein Ibrahim,Resident Engineer on the Wad Medani-Sennar-Kosti project for their whole-hearted help and cooperation in theconstruction of the dry compaction trials.

The work described in this paper formspart of' the programme of the Transport andRoad Research.Laboratory, and is publishedby permission of the Director.

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British Standards Institution.' 1975.Methods of testing soils for civilengineering purposes. British Standard1377:1975. London. British StandardsInstitution.

Chaigne, P., Blivet, J.C. 1971.Compactage par vibration a teneur en-eau nulle. Bulletin de Liaison desLaboratoires des Ponts~et Chauss6es,8/9 n54 p 45-48.

Clegg, B. 1977. Field assessment of theImpact Soil Tester. Australian RoadResearch Board. Research Report ARENo. 76.

Clifford, J.M. 1976. Impact rolling andconstruction techniques. AustralianRoad Research Board Proceedings, Vol. 8Session 13.

Forssblad, L. 1974. Vibratory compactionof soil, rock fill and asphalticconcrete. Australian Road ResearchBoard Proceedings Vol. 7, Part 6.

Grace, H., Cocksedge, J.E. 1978. Recentinvestigations into the dry compactionof sand. IRF Regional Conference forMiddle East and North Africa, 9-15April, Cairo, Egypt.

International Road Federation. 1978.UNDP Highway program serves Africa'sSahel region. World Highways, Vol.XXIX, No. 9 International RoadFederation.

Kabbaj, M. 1979. National report -

Morocco - Question V Low cost and lowtraffic roads. PIARC XVIth World RoadCongress. Vienna.

Lee, P.Y. 1976. Study of irregularcompaction curves. Soil specimenpreparation for laboratory testing,ASTM STP 599: 278-288 American Societyfor Testing and Materials.

Lee, P.Y., Suedkamp, R.J. 1972.Characteristics of irregularly shapedcompaction curves of-soils. HighwayResearch Record No. 381. Washington,Highway Research Board.

Lewis, W.A. 1954. Further studies in thecompaction of soil and the performanceof' compaction plant. Road ResearchTechnical Paper No. 33. Department ofScientific and Industrial Research,Road Reseaj~ch Laboratory, London .HMSO.

Lewis, W.A., Parsons, A.W. 1961. Theperformance of compaction plant in thecompaction of two types of granularbase material. Road Research TechnicalPaper No. 53. Department of Sceintificand Industrial Research, Road ReserachLaboratory, London HMSO.

Morris, P.E.A Review.Australian

( ed). 1975. Compaction,ARR Report No. 35.Road Research Board.

Mtango, H. 1979. An investigation intothe dry compaction of lateritic sandygravel. Norwegian Road ResearchLaboratory (Vegdirektoratet Veglabora-toriet) Internal Report No. 859 Oslo.

Republique Algerienne Democratique etPopulaire. 1972. Planches d'essai decompactage a sec de Tamanrasset.Minist~re des Travaux Publics. Repub-lique Algdrienne Democratique etPopulaire.

Todres, H.A. 1970. The use of additivesto reduce the quantity of water requiredfor the compaction of soil. InternalReport RC/4/70. National Institute forRoad Research. South Africa.

Van Rooyen, M., Wessels, C.J. 1967a.Report to the NIRR, CSIR on compactionof soil in arid areas. Part I -

Literature survey. NIRR Report RS/13/67.Department of Civil Engineering,University of Pretoria.

Van Rooyen, M., Wessels, C.J. 1967b.ibid - Part II - Laboratory investigation.Rs/14/67.

Van Rooyen, 1M., Wessels, C.J. 1967c.ibid - Part III - Field investigation.RS/15167.

Crown Copyright 1979. Any views expressedin this Paper are not necessarily those ofthe Department of the Environment or ofthe Department of Transport. Extractsfrom the text may be reproduced, exceptfor conmmercial purposes, provided thesource is acknowledged. Reproduced bypermission of the Controller of HerBritannic Majesty' s Stationery Office.

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