《道路与桥梁建筑材料》课程教学资源（文献资料）COHESIVE AND NON-COHESIVE SOILS and UNBOUND GRANULAR MATERIALS for BASES and SUB-BASES in ROADS

COHESIVEANDNON-COHESIVESOILSandUNBOUNDGRANULARMATERIALSforBASESandSUB-BASESinROADSProf.Dr.Ir.AndreA.A.MolenaarNootdorp,January2015a.a.a.molenaar@tudelft.nl

COHESIVE AND NON-COHESIVE SOILS and UNBOUND GRANULAR MATERIALS for BASES and SUB-BASES in ROADS Prof. Dr. Ir. André A.A. Molenaar Nootdorp, January 2015 a.a.a.molenaar@tudelft.nl

ForewordSoils such as clay and sand, and unbound granular materials such as gravel and crushedrock,are the backbone of road and railway structures.Without proper attention to thesubgrade, subbase and base, road and railway structures will fail within a short period oftime.Soils and unbound granular materials are complex materials because they have formed fromrocks through weathering and transportation of the weathered material by air,water or ice.Water and vegetation play also a large role in the characteristics of the soils that are actuallyformed.Therefore it will be obvious that any engineer who is working in the road or railwayengineering industry should haveabasic understanding of the behaviourof thesematerials.Thelecturenotes togetherwiththeclasses that will begiven onthis subject will give you thatbasic understanding.The reader will observe that the lecture notes in front of him/her cover a substantial amountof subjects. The reason for this is that the SANRAL Chair in Road Engineering at theUniversity of Stellenbosch and the Chair of Road Engineering at the Delft University ofTechnologyhavedecided todevelopa set of lecturenotes onpavement related topics thatare of interest not only to South-African and Dutch students but also to students of otherparts of the world.Thelecturenotes havebeenpreparedusing lots of information andnot all theinformation isdeveloped by the author himself. Especially on the topic of soil forming and clay mineralogyinformation isdrawn from existing textbooksand sometimes entire sections from thosetextbooksarereproduced.Wherethisisthecase,thisisexplicitlymentioned.Othermainsources on these two topics were the lecture notes taken on these topics by prof.Jenkinswhen hewas still a student at the University of Natal and byprof.Molenaar when hewasstudying at the University of Texas at Austin. Since these hand written notes and thehandoutsaccompanyingthemarenotofficial literature,itisverydifficulttorefertothemTherefore theauthor likes tomention herethat these notes werea sourceof informationandhe likestothank prof.Everitt andprof.Schreinerof theUniversityof Nataland prof.KennedyoftheUniversityofTexasforpreparingthem.Amajorsourceof information wastheresearchdoneonvarioustypesof soil and granularmaterials inSouthAfricaandtheworkdoneattheDelft Universityof Technologyonsometropical soils as well as sands and granular materials. The literature used is mentioned in theliteratureoverview.The author likes to thank especially prof. Jenkins of the University of Stellenbosch in South-Africa for the proof reading,his valuable comments and actual writing of some sections. Alsoir.Houbenof theDelftUniversityisthankedforproofreadingandthecommentsmade.In spiteall the efforts made,some errors might always occur.The reader is therefore invitedto send his comments by email to theauthor so that corrections and improvements can bemade.I wish you much pleasure with reading and studying the material and wish you alreadysuccess when youareplanning to doan exam on this topic.January 2015A.A.A. Molenaara.a.a.molenaar@citg.tudelft.nl

Foreword Soils such as clay and sand, and unbound granular materials such as gravel and crushed rock, are the backbone of road and railway structures. Without proper attention to the subgrade, subbase and base, road and railway structures will fail within a short period of time. Soils and unbound granular materials are complex materials because they have formed from rocks through weathering and transportation of the weathered material by air, water or ice. Water and vegetation play also a large role in the characteristics of the soils that are actually formed. Therefore it will be obvious that any engineer who is working in the road or railway engineering industry should have a basic understanding of the behaviour of these materials. The lecture notes together with the classes that will be given on this subject will give you that basic understanding. The reader will observe that the lecture notes in front of him/her cover a substantial amount of subjects. The reason for this is that the SANRAL Chair in Road Engineering at the University of Stellenbosch and the Chair of Road Engineering at the Delft University of Technology have decided to develop a set of lecture notes on pavement related topics that are of interest not only to South-African and Dutch students but also to students of other parts of the world. The lecture notes have been prepared using lots of information and not all the information is developed by the author himself. Especially on the topic of soil forming and clay mineralogy information is drawn from existing textbooks and sometimes entire sections from those textbooks are reproduced. Where this is the case, this is explicitly mentioned. Other main sources on these two topics were the lecture notes taken on these topics by prof. Jenkins when he was still a student at the University of Natal and by prof. Molenaar when he was studying at the University of Texas at Austin. Since these hand written notes and the handouts accompanying them are not official literature, it is very difficult to refer to them. Therefore the author likes to mention here that these notes were a source of information and he likes to thank prof. Everitt and prof. Schreiner of the University of Natal and prof. Kennedy of the University of Texas for preparing them. A major source of information was the research done on various types of soil and granular materials in South Africa and the work done at the Delft University of Technology on some tropical soils as well as sands and granular materials. The literature used is mentioned in the literature overview. The author likes to thank especially prof. Jenkins of the University of Stellenbosch in South￾Africa for the proof reading, his valuable comments and actual writing of some sections. Also ir. Houben of the Delft University is thanked for proof reading and the comments made. In spite all the efforts made, some errors might always occur. The reader is therefore invited to send his comments by email to the author so that corrections and improvements can be made. I wish you much pleasure with reading and studying the material and wish you already success when you are planning to do an exam on this topic. January 2015 A.A.A. Molenaar a.a.a.molenaar@citg.tudelft.nl

Contents11.Introduction12. Grains, water and air43. Particle size distribution and interaction with moisture of soils and granular materials134.Soil formingandpedological identificationsystems154.2 Soil formation andpedological identification system185.Mineralogyand soil structure185.1Mineralogy205.2Claymineralogy245.3 The electrical charge on a soil particle and the interaction with water285.4Flocculation and dispersion6.Effectsof compactiononthestructureofasoiland itsengineeringproperties296.1 Shrinkage30306.2 Swelling316.3 Stress - deformation characteristics326.4Influenceofcompactionmethod337.Compactionofcohesivesoils378. Swelling clays378.1 Gradation and plasticity characteristics408.2 Moisture-density relationships, CBRand resilient modulus428.3 Stabilisation with lime, effects on plasticity8.4 Stabilisation with lime and effects on moisture -density,CBR and resilient modulus (M.)438.5Closure46479.Laterites479.1 Formation of laterite489.2 Weathering process499.3Profiledevelopment519.4Theprocessofconcretionarydevelopment529.5Someengineeringcharacteristics629.6Failure, resilientand permanent deformation characteristics679.7 Closure6810.UnboundGranularMaterials7810.2Inventoryof baseand sub-basematerials in theNetherlands8110.3Backgroundontheuseofsand10.4 Principles of the mechanical behaviour of unbound granular (sub)base materials and91sands10.5Factors influencingthemechanicalcharacteristicsof unbound basematerialsand sands9910310.6Parameter estimation procedures11510.7Specifications11. Examples of some problematic unbound granular materials and treatments to upgrade them.11611611.1 Introduction11611.2 Upgrading an Ethiopian natural gravel12111.3ModifyingCinderfromEthiopia13011.4VolcanicmaterialfromYemen13612Compactionof granularsoils13612.1Introduction14212.2Principlesofcompactinggranularmaterials14312.3Compactionequipment12.4 Specifications and field control forsoils15015212.5Rollerapplications

Contents 1. Introduction 1 2. Grains, water and air 1 3. Particle size distribution and interaction with moisture of soils and granular materials 4 4. Soil forming and pedological identification systems 13 4.2 Soil formation and pedological identification system 15 5. Mineralogy and soil structure 18 5.1 Mineralogy 18 5.2 Clay mineralogy 20 5.3 The electrical charge on a soil particle and the interaction with water 24 5.4 Flocculation and dispersion 28 6. Effects of compaction on the structure of a soil and its engineering properties 29 6.1 Shrinkage 30 6.2 Swelling 30 6.3 Stress – deformation characteristics 31 6.4 Influence of compaction method 32 7. Compaction of cohesive soils 33 8. Swelling clays 37 8.1 Gradation and plasticity characteristics 37 8.2 Moisture – density relationships, CBR and resilient modulus 40 8.3 Stabilisation with lime, effects on plasticity 42 8.4 Stabilisation with lime and effects on moisture – density, CBR and resilient modulus (Mr) 43 8.5 Closure 46 9. Laterites 47 9.1 Formation of laterite 47 9.2 Weathering process 48 9.3 Profile development 49 9.4 The process of concretionary development 51 9.5 Some engineering characteristics 52 9.6 Failure, resilient and permanent deformation characteristics 62 9.7 Closure 67 10. Unbound Granular Materials 68 10.2 Inventory of base and sub-base materials in the Netherlands 78 10.3 Background on the use of sand 81 10.4 Principles of the mechanical behaviour of unbound granular (sub)base materials and sands 91 10.5 Factors influencing the mechanical characteristics of unbound base materials and sands 99 10.6 Parameter estimation procedures 103 10.7 Specifications 115 11. Examples of some problematic unbound granular materials and treatments to upgrade them. 116 11.1 Introduction 116 11.2 Upgrading an Ethiopian natural gravel 116 11.3 Modifying Cinder from Ethiopia 121 11.4 Volcanic material from Yemen 130 12 Compaction of granular soils 136 12.1 Introduction 136 12.2 Principles of compacting granular materials 142 12.3 Compaction equipment 143 12.4 Specifications and field control for soils 150 12.5 Roller applications 152

15313Moisture in subgrades and (sub-) base layers15313.1Introduction15413.2 Estimating water content in highway subgrades15513.3Estimationofsoil-waterpotentialcurvesforsubgradesoils(pFcurves)15713.4Estimationofwaterpotentialcurvesforunboundmaterials(pF)curves15813.5Methodtoestimateequilibriummoisturecontent15813.6Practicalconsiderations159References162AppendixA:Laboratorytests,sieveanalysisandplasticity178Appendix B: Laboratory tests, compaction and bearing capacity200AppendixC:TestsusedbySemmelink204Appendix D: Dutch and South African specifications for unbound materials and sands2

2 13 Moisture in subgrades and (sub-) base layers 153 13.1 Introduction 153 13.2 Estimating water content in highway subgrades 154 13.3 Estimation of soil-water potential curves for subgrade soils (pF curves) 155 13.4 Estimation of water potential curves for unbound materials (pF) curves 157 13.5 Method to estimate equilibrium moisture content 158 13.6 Practical considerations 158 References 159 Appendix A: Laboratory tests, sieve analysis and plasticity 162 Appendix B: Laboratory tests, compaction and bearing capacity 178 Appendix C: Tests used by Semmelink 200 Appendix D: Dutch and South African specifications for unbound materials and sands 204

1.IntroductionSoils and granular materials are very important building materials in road and railwayengineering. They are used as subgrade, as subbase and as base for pavements for roads,airfields etc as well as for railway structures.Knowledge on thecharacteristicsand behaviourof soils and granular materials is therefore essential for any road and railway engineer. Thisknowledge deals with the response of the materials when subjected to three dimensionalstatesofstress,theirbehaviourinrelationtowaterandfrost,etcBy nature, soils and granular materials are rather difficult materials to deal with. Particularlynatural soils and gravels show diversebehaviourasa consequenceof geological historythathad an influence on the mineralogical composition, the particle shape and particle sizedistribution. Moreover the actual degree of compaction and moisture content are of greatimportance.Oneshould beremindedthough that in many countries,of which the Netherlands is agoodexample,unboundbasematerialsarenotnatural materialsanymorebutprocessedmaterialsbeing the result of recycling of old concrete and masonry that result from e.g. demolishingbuildings. Also slags from steel factories and blast furnaces are commonly used for roadbasesandsubbases.All thismeansthatthere isawidevarietyof materialsavailableonthemarketnowadaysthatallowgoodqualityroadbasesand subbasestobebuilt.In this set of lecture notes we will deal with those characteristics of soils and granularmaterials that are important for engineering purposes.Much emphasis will therefore beplaced on the mechanical characteristics of those materialsas a function of factors like thegradation, the characteristics of thefines, the degree of compaction etc..2.Grains,waterandairSoils can be regarded as compositions of solid particles, water and air (figure 1)Figure 1 Soil: a composition of solid particles, water and air.The grains form the rigid part of this system, whereas the water and air fill the voids betweenthe grains. The size and shape of the grains, the particle size distribution and the ratiobetween solid material, water and air determine the characteristics of the soil. Severalparameters for this soil system are defined.Figure 2 shows an idealization of the soil systeminwhichthethreecomponentsareseparatedandrepresentedbythreevolumes.1

1 1. Introduction Soils and granular materials are very important building materials in road and railway engineering. They are used as subgrade, as subbase and as base for pavements for roads, airfields etc as well as for railway structures. Knowledge on the characteristics and behaviour of soils and granular materials is therefore essential for any road and railway engineer. This knowledge deals with the response of the materials when subjected to three dimensional states of stress, their behaviour in relation to water and frost, etc. By nature, soils and granular materials are rather difficult materials to deal with. Particularly natural soils and gravels show diverse behaviour as a consequence of geological history that had an influence on the mineralogical composition, the particle shape and particle size distribution. Moreover the actual degree of compaction and moisture content are of great importance. One should be reminded though that in many countries, of which the Netherlands is a good example, unbound base materials are not natural materials anymore but processed materials being the result of recycling of old concrete and masonry that result from e.g. demolishing buildings. Also slags from steel factories and blast furnaces are commonly used for road bases and subbases. All this means that there is a wide variety of materials available on the market nowadays that allow good quality road bases and subbases to be built. In this set of lecture notes we will deal with those characteristics of soils and granular materials that are important for engineering purposes. Much emphasis will therefore be placed on the mechanical characteristics of those materials as a function of factors like the gradation, the characteristics of the fines, the degree of compaction etc. 2. Grains, water and air Soils can be regarded as compositions of solid particles, water and air (figure 1). Figure 1 Soil: a composition of solid particles, water and air. The grains form the rigid part of this system, whereas the water and air fill the voids between the grains. The size and shape of the grains, the particle size distribution and the ratio between solid material, water and air determine the characteristics of the soil. Several parameters for this soil system are defined. Figure 2 shows an idealization of the soil system in which the three components are separated and represented by three volumes

WeightVolumeWAirWWaterWVV.WSolidSFigure2Idealizedthree-phasesoil system.The meaning of the symbols used in figure 2 is as follows:vw==total volumetotal weightVa=Wa=volume of airweight of air = 0VwWw==volume of waterweightofwater=Vw*YwVs=Wsvolumeof solids=weight of solids = V, *ysVv==volumeofvoidsdensity of waterYw=Ysdensity of solidsUsing these values some important quantities, which are often used in road engineering,arecalculated:Dry densitypdWsweight of solids2N/mPd =Jtotal volumeWatercontentwWwweight of waterL*100%*100%[%]W=Wsweight of solidsVoid ratio eVyvolume of voids[H]e=Vsvolumeof solidsPorosity nVvvolumeofvoids[H]n=Vtotal volume2

2 Figure 2 Idealized three-phase soil system. The meaning of the symbols used in figure 2 is as follows: V = total volume W = total weight Va = volume of air Wa = weight of air = 0 Vw = volume of water Ww = weight of water = Vw * w Vs = volume of solids Ws = weight of solids = Vs * s Vv = volume of voids w = density of water s = density of solids Using these values some important quantities, which are often used in road engineering, are calculated: Dry densityd d =   3 N/m total volume weight of solids V Ws  Water content w W = * 100% % weight of solids weight of water * 100% Ws Ww  Void ratio e e =   volume of solids volume of voids s V v V Porosity n n =   total volume volume of voids V v V

DegreeofsaturationS,Vw*100%weight of water * 100%[%SrVvvolumeof voidsEspeciallythedrydensityandthewatercontentare of importancebecausetheystronglyinfluence the structural behaviour of a given soil or granular material. That is whytheseparametersmustbespecified whena roadhastobebuilt.Compactiontests inthelaboratoryaretherefore performed to establishtheoptimumvalues.These compactiontests will bedescribed in a separate paragraph.The degree of saturation is strongly related with soil suction and pore pressure.Soil suctiondevelops withlowerdegreesof saturation,especially infinegrained soils,andleadstohigherstiffnessesduetoextrainducedcompressivestresses,whereasporepressuresmaydevelopifthe degree of saturation reaches 100%,resulting in reduced effective stresses and possiblyshear.The void ratio e and porosity n are related to each other following:11and e:n1+e1-nAnother importantparameter is the specified gravity Gs,of thegrains, in some countriesalsocalled relative density.It is defined as the ratio between themass of dry solids and the massof distilled water displaced by the dry soil particles. As it is a ratio between two quantitieswith thesamedimension,the specificgravity itself isdimensionless:Ws *1weight of solids[-1G, =VsvolumeofsolidsPH20PH20The specific gravity is used in the calculation of the degree of saturation and in thecalculationofthesedimentationspeedofsoilparticleswithadiameterlessthan75um.Thiswill be discussed in the paragraph on particle size analysis. In the case of porous materials itshould be noted that enclosed pores in the material are supposed to be a part of thematerial.Inthenextexamplethecalculationof thedegreeof saturationisdemonstratedforaspecificDutch sand under conditions of maximum density Pd.max and optimum water content WoptExampleGiven1668 [kg/m"]Pd.max-=15.7 [%]Wopt=Gs2.65 [-]Consider 1 m3 of compacted material. The volume of the solids is then calculated from thedry density and the specific gravity of the grains, according to:VsVolume of solids=1668 / 2650 = 0.629 [m′]The volume of voids and the volume of the solids together make 1 m3, so that the volume ofthe voids is equal to:Vv1 - 0.629 = 0.371 [m′]Volumeof voids=3

3 Degree of saturation Sr Sr = * 100% % volume of voids weight of water * 100% v V Vw  Especially the dry density and the water content are of importance because they strongly influence the structural behaviour of a given soil or granular material. That is why these parameters must be specified when a road has to be built. Compaction tests in the laboratory are therefore performed to establish the optimum values. These compaction tests will be described in a separate paragraph. The degree of saturation is strongly related with soil suction and pore pressure. Soil suction develops with lower degrees of saturation, especially in fine grained soils, and leads to higher stiffnesses due to extra induced compressive stresses, whereas pore pressures may develop if the degree of saturation reaches 100%, resulting in reduced effective stresses and possibly shear. The void ratio e and porosity n are related to each other following: 1 e 1 n   and 1 n 1 e   Another important parameter is the specified gravity Gs , of the grains, in some countries also called relative density. It is defined as the ratio between the mass of dry solids and the mass of distilled water displaced by the dry soil particles. As it is a ratio between two quantities with the same dimension, the specific gravity itself is dimensionless: Gs =   o 2 H ρ 1 * volume of solids weight of solids o 2 H ρ 1 * s V Ws The specific gravity is used in the calculation of the degree of saturation and in the calculation of the sedimentation speed of soil particles with a diameter less than 75 m. This will be discussed in the paragraph on particle size analysis. In the case of porous materials it should be noted that enclosed pores in the material are supposed to be a part of the material. In the next example the calculation of the degree of saturation is demonstrated for a specific Dutch sand under conditions of maximum density d.max and optimum water content wopt. Example Given d.max = 1668 [kg/m 3 ] wopt = 15.7 [%] Gs = 2.65 [-] Consider 1 m3 of compacted material. The volume of the solids is then calculated from the dry density and the specific gravity of the grains, according to: Volume of solids Vs = 1668 / 2650 = 0.629 [m3 ] The volume of voids and the volume of the solids together make 1 m3 , so that the volume of the voids is equal to: Volume of voids Vv = 1 – 0.629 = 0.371 [m3 ]

Thewatercontentasrelatedtothedrymassofthematerial containedin1m3,is15.7%,which impliesthattheamountofwater equals:Weight of waterWw0.157 * 1668 = 262 [kg]=For normal engineering purposes the density of water is 1000 [kg/m'j. For the volume ofwaterthensimplyfollows:Vw262 / 1000 = 0.262 [m2]VolumeofwaterThe degree of saturation is calculated from the volume of water related to the volume ofvoids, expressed asa percentage:Degree of saturationSrVw/V,=0.262/0.371=71%Itisnoteworthythatatoptimumwatercontentsome70%ofthevoidsisfilledwithwater.However, for sands this is a quitecommon value.3.Particlesize distributionandinteractionwithmoisture of soils and granular materialsSoilsandgranularmaterialsconsistofanarrangementofparticles.Inbetweentheparticlesthere are voids and these voids may be (partly) filled with moisture. Typical examples of sucharrangements are given in figure 3.(a) Aggregate with(b) Aggregate with(c) Aggregate withno finessufficient fines forgreat amount of finesmaximum densityGrain-to-grain contactGrain-to-grain contactGrain-to-grain contactWith increased resistancedestroyed, aggregatefloating'in soilAgainst deformationVariable densityIncreased densityDecreased densityPerviousPractically imperviousPractically imperviousNon-frost-susceptibleFrost-susceptibleFrost-susceptibleHigh stability ifHigh stability inLow stabilityConfined, low ifconfinedorunconfinedUnconfinedconditionsNot affected byNot affected byGreatly affected byAdversewaterconditionadversewaterconditionadversewaterconditionVery difficult toModerately difficult toNot difficult tocompactcompactcompactFigure 3 Three physical states of soil-aggregate mixtures [1].4

4 The water content as related to the dry mass of the material contained in 1 m3 , is 15.7%, which implies that the amount of water equals: Weight of water Ww = 0.157 * 1668 = 262 [kg] For normal engineering purposes the density of water is 1000 [kg/m3 ]. For the volume of water then simply follows: Volume of water Vw = 262 / 1000 = 0.262 [m3 ] The degree of saturation is calculated from the volume of water related to the volume of voids, expressed as a percentage: Degree of saturation Sr = Vw / Vv = 0.262 / 0.371 = 71% It is noteworthy that at optimum water content some 70% of the voids is filled with water. However, for sands this is a quite common value. 3. Particle size distribution and interaction with moisture of soils and granular materials Soils and granular materials consist of an arrangement of particles. In between the particles there are voids and these voids may be (partly) filled with moisture. Typical examples of such arrangements are given in figure 3. (a) Aggregate with (b) Aggregate with (c) Aggregate with no fines sufficient fines for great amount of fines maximum density Grain-to-grain contact Grain-to-grain contact Grain-to-grain contact With increased resistance destroyed, aggregate Against deformation ‘floating’ in soil Variable density Increased density Decreased density Pervious Practically impervious Practically impervious Non-frost-susceptible Frost-susceptible Frost-susceptible High stability if High stability in Low stability Confined, low if confined or unconfined Unconfined conditions Not affected by Not affected by Greatly affected by Adverse water condition adverse water condition adverse water condition Very difficult to Moderately difficult to Not difficult to compact compact compact Figure 3 Three physical states of soil-aggregate mixtures [1]

Figure 3 shows three soil particle arrangements but a fourth one should be identified as well.That is the particle arrangement where no coarse particles are present and the soil onlyconsists of fineparticlesIn figure 3, the coarse particles are stones with a specific hardness which can be anythingranging fromgranite to siliceous river gravel.The fine particles are usually products of furtherdeterioration or weathering of the parent material.As will be discussed later on, especiallythefineparticles interactwithwaterwhichmeansthatthebehaviourof thefines inrelationto water is important information.If those fine particles are e.g.clay,then structure b and cwill beratherstrongwhendrybecauseclayisahardandstrongmaterial whendry.Ontheother hand structurec will loose its strength when wet because clay has only limited strengthwhen wet. Particle arrangement b is much less affected by wet conditions because in thatcasethecoarseparticles willprovidethetransferthe loads.What becomesclearfromthispicture isthat oneneedstoknowtheparticle sizedistributionandthebehaviourofthefinesinrelationwithmoistureParticulartypesofsoilshowever,suchascollapsingsoils,haveastructureliketheoneshownin figure 4.Figure 4 Honeycomb structure in a granular soil [1].Thistype of"houseof cards"structure might havea highbearing capacityfor static loads,but might collapse easily under dynamic loads. In addition, if the moisture content increasesaftera static load is applied,this can sometimes result indramatic collapse settlement.In thisparticular case one needs not only to know the grain size distribution but also the bulkdensityofthesoilmassandthespecificdensityofthegrains.Ifthebulkdensityofthesoilmass is muchlower than the specific densityof thegrains, thenoneknowsthat the soil massmust contain a large amount of voids.Examplesofparticlesizedistributioncurvesareshown infigure5.CurveA istypicalfor an uniformly graded sand.CurveB is typical fora well graded silty-sandgravel, while curve C is typical for a gap graded material. Gap graded means in this case thattherearenoparticles available witha diameterbetween0.6and3mm.Figure 5b shows that all four grain size distribution curves indicate the presence of clay,silt,sand and to some extent gravel.This makes the definition of names a rather complex taskand in orderto get someorderinthisatriangular classification chart, shown in figure6,hasbeen developed. In this figure all seven respective grain size distribution curves arerepresented (A to G) with the exclusion of all particles > 2 mm i.e., so all the percentages hadto be adjusted.5

5 Figure 3 shows three soil particle arrangements but a fourth one should be identified as well. That is the particle arrangement where no coarse particles are present and the soil only consists of fine particles. In figure 3, the coarse particles are stones with a specific hardness which can be anything ranging from granite to siliceous river gravel. The fine particles are usually products of further deterioration or weathering of the parent material. As will be discussed later on, especially the fine particles interact with water which means that the behaviour of the fines in relation to water is important information. If those fine particles are e.g. clay, then structure b and c will be rather strong when dry because clay is a hard and strong material when dry. On the other hand structure c will loose its strength when wet because clay has only limited strength when wet. Particle arrangement b is much less affected by wet conditions because in that case the coarse particles will provide the transfer the loads. What becomes clear from this picture is that one needs to know the particle size distribution and the behaviour of the fines in relation with moisture. Particular types of soils however, such as collapsing soils, have a structure like the one shown in figure 4. Figure 4 Honeycomb structure in a granular soil [1]. This type of “house of cards” structure might have a high bearing capacity for static loads, but might collapse easily under dynamic loads. In addition, if the moisture content increases after a static load is applied, this can sometimes result in dramatic collapse settlement. In this particular case one needs not only to know the grain size distribution but also the bulk density of the soil mass and the specific density of the grains. If the bulk density of the soil mass is much lower than the specific density of the grains, then one knows that the soil mass must contain a large amount of voids. Examples of particle size distribution curves are shown in figure 5. Curve A is typical for an uniformly graded sand. Curve B is typical for a well graded silty-sand gravel, while curve C is typical for a gap graded material. Gap graded means in this case that there are no particles available with a diameter between 0.6 and 3 mm. Figure 5b shows that all four grain size distribution curves indicate the presence of clay, silt, sand and to some extent gravel. This makes the definition of names a rather complex task and in order to get some order in this a triangular classification chart, shown in figure 6, has been developed. In this figure all seven respective grain size distribution curves are represented (A to G) with the exclusion of all particles  2 mm i.e., so all the percentages had to be adjusted

BRITISHSTANDARD SIEVESIZE6-32037-5200cOrFigure5aExamplesofparticlesizedistributioncurvesforsandsandgravels[2]BRITISHSTANDARO SIEVE SIZESA.GAAVEFigure5b Examplesofparticlesizedistributioncurvesforsandsandgravels[2]

6 Figure 5a Examples of particle size distribution curves for sands and gravels [2]. Figure 5b Examples of particle size distribution curves for sands and gravels [2]