S.ANCCLAYDClay40oSiltycloyclayGSondy &'silty cloySondy claycowwithsit20Cloyey &Clayey sltClayey sandSandy siltSutSlighty clayey sondSondy sit`ES0sanods801004060B20FullerSILTFigure6Triangularclassificationchart[2].Notethat at the bottomof figure5,names aregiven to the different particle sizes.It shouldbe recognised however that these names are not universal names; this is illustrated in table1. This implies that one must be careful in indicating materials by name when workingabroad, since one might not use the same grain sizes to indicate a material.Range [mm]NetherlandsUnited KingdomUSAClay<0.002<0.002<0.005silt0.002 - 0.0630.0020.0600.005-0.075Sand0.063 20.060 20.0754.75Gravel2 - 632 604.75 - 76.2Cobbles> 6360 - 200> 76.2Boulders-> 200-Table 1 Particle size ranges in the Netherlands, United Kingdom and the USA.Figure 5a also shows the so-called Fuller distribution.If a particle arrangement has a particledistribution like that of a Fuller curve then one knows that that arrangement has the densestpacking possible.TheFullercurveisgivenby:P = 100 V (D/Dmax)Where:P=percentagebymassofparticlessmallerthandiameterD,Dmax=maximumparticlesize(infigure3thisis75mm)Particle size distributions are determined by means of sieving. Sieving procedures include drysieving, wet sieving and ultrasonic sieving while the determination of the particle sizedistribution of thefine fraction involves sedimentation tests.These procedures aredescribedin Appendix A.Reference is also madeto laboratory handbooks such as [2] wheretheprocedures to be followed are precisely described. Also reference is made to the ASTM(American SocietyforTesting Materials)manuals whichcontaindetailed information.In the following sections reference will be made to specific sieve numbers. In order tounderstand the meaning of thesenumbers,an overview of them is given in table2.7
7 Figure 6 Triangular classification chart [2]. Note that at the bottom of figure 5, names are given to the different particle sizes. It should be recognised however that these names are not universal names; this is illustrated in table 1. This implies that one must be careful in indicating materials by name when working abroad, since one might not use the same grain sizes to indicate a material. Range [mm] Netherlands United Kingdom USA Clay 0.002 0.002 0.005 Silt 0.002 – 0.063 0.002 – 0.060 0.005 – 0.075 Sand 0.063 – 2 0.060 – 2 0.075 – 4.75 Gravel 2 – 63 2 – 60 4.75 – 76.2 Cobbles 63 60 – 200 76.2 Boulders - 200 - Table 1 Particle size ranges in the Netherlands, United Kingdom and the USA. Figure 5a also shows the so-called Fuller distribution. If a particle arrangement has a particle distribution like that of a Fuller curve then one knows that that arrangement has the densest packing possible. The Fuller curve is given by: P = 100 (D/Dmax) Where: P = percentage by mass of particles smaller than diameter D, Dmax = maximum particle size (in figure 3 this is 75 mm). Particle size distributions are determined by means of sieving. Sieving procedures include dry sieving, wet sieving and ultrasonic sieving while the determination of the particle size distribution of the fine fraction involves sedimentation tests. These procedures are described in Appendix A. Reference is also made to laboratory handbooks such as [2] where the procedures to be followed are precisely described. Also reference is made to the ASTM (American Society for Testing Materials) manuals which contain detailed information. In the following sections reference will be made to specific sieve numbers. In order to understand the meaning of these numbers, an overview of them is given in table 2
ASTMBS (metric)NEN25603 inch75 mmC-31.52 inch63mmC-22.41.5 inch50mmC-20C-161 inch37.5mm3/4 inch28mmC- 11.2C-83/8 inch20 mmNo4(4.75 mm)14mmC-5.6No8(2.38 mm)10mmC- 4No10(2.00 mm)6.3mm2.8 mmNo205 mm2 mm(850 μm)No403.35 mm1.4mm(425 μm)No60(250 μm)2 mm1 mmNo 140(106 μm)1.18mm710 μmNo 200(75 μm)600 μm500μm425 μm355 μm300 μm250 μm212 μm180 μm150 μm125 μm63 μm90 μm63 μmTable 2 ASTM, BS and NEN sieve Series.As mentioned before,the fine particles interact with moisture.Table 3 gives an overview ofthe different states that can be recognised together with a number of limits that are used tocharacterise the interaction of the fines with moisture. These limits are called the Atterberglimits.The Atterberg limitsare determined onthe material with a diameter smaller than 425μm.SOLIDSEMISOLIDPLASTICLIQUIDSUSPEN-PhaseSTATESTATESTATESTATESION--Water content decreasingWoterLimitsDryShrinkogeLiquidsoilLimitLimitSLPLLLPlasticity,IndexVolumeVolume decreasingShrinkogeconstantHard toMoter-heldConditionworkableStickySlurrystiftIsuspensionShearShear strength increasingStrengthNegligible to nl(~170)(~1-7)(kN/m2)+2+孔MoistureCContentP1HTable 3 Phases of soil and the Atterberg limits [2].8
8 ASTM BS (metric) NEN 2560 3 inch 75 mm C- 31.5 2 inch 63mm C- 22.4 1.5 inch 50 mm C- 20 1 inch 37.5 mm C- 16 ¾ inch 28 mm C- 11.2 3/8 inch 20 mm C- 8 No 4 (4.75 mm) 14 mm C- 5.6 No 8 (2.38 mm) 10 mm C- 4 No 10 (2.00 mm) 6.3 mm 2.8 mm No 20 (850 m) 5 mm 2 mm No 40 (425 m) 3.35 mm 1.4 mm No 60 (250 m) 2 mm 1 mm No 140 (106 m) 1.18 mm 710 µm No 200 ( 75 m) 600 µm 500 µm 425 µm 355 µm 300 µm 250 µm 212 µm 180 µm 150 µm 125 µm 63 µm 90 µm 63 µm Table 2 ASTM, BS and NEN sieve series. As mentioned before, the fine particles interact with moisture. Table 3 gives an overview of the different states that can be recognised together with a number of limits that are used to characterise the interaction of the fines with moisture. These limits are called the Atterberg limits. The Atterberg limits are determined on the material with a diameter smaller than 425 m. Table 3 Phases of soil and the Atterberg limits [2]
In Appendix A it is discussed how the liquid limit, plastic limit and shrinkage limit aredetermined.Thereaderisalsoreferred tolaboratorytextbookssuchasreference[2]In the past, systems have been developed to classify soils based on their particle sizedistribution and their Atterberg limits.The best known classification systems are theAASHTOand Uscs classification system.Since both systems are widely used to classify soils andgranular materials, some attention will bepaid to them hereafter.AASHTOSoilClassificationSystem:The AASHTO system is developed by the Association of American State Highway andTransportation Officials. This implies that this system and in particular the boundaries thatareused,areespeciallydevelopedforroadpurposes.The system contains seven classes to identify soils and granular materials. The groups rangefrom A-1 to A-7.Materials belonging to groups A-1to A-3 are coarse grained materials whilematerials belonging to groups A-4 to A-7 are fine grained materials. The A-1 and A-2 groupshaveasub-ratingwhichwill beexplainedhereafter.A material is rated as a coarse material (A-1, A-2, or A-3) if less than 35% passes the no. 200sieve.Theclassificationproceedsthenasfollows.Thematerial is anA-1material if:Lessthan25%passes theno.200sieveand lessthan50%passes theno.40sieve.Howeverif:Less than 15% passes the no. 200 sieve and less than 30% passes the no. 40 sieve and lessthan 50% passes the no. 10 sieve and PI < 6, then the material is rated as an A-1-a material.Iflessthan25%passestheno.200sieveandlessthan50%passestheno.40sieveandPI<6,thenthematerialisratedasanA-1-bmaterial.If the material is rated as a coarse material but not as an A-1 material, then it is either an A-2orA-3material.The next step is to determine whether it is an A-3 material or not.It is an A-3 material if:Lessthan10%passestheno.200sieveandmorethan50%passestheno.40sieveandthematerial is non plastic.If the material is rated as a coarse material but not as an A-1 or an A-3 material, then it is anA-2 material. It might then be rated as an A-2-4, A-2-5, A-2-6 or an A-2-7 material. Thisdepends on theplasticity limits of thematerial passing the no.40 sieve.For this theplasticitychart shown in figure 7 is used.9
9 In Appendix A it is discussed how the liquid limit, plastic limit and shrinkage limit are determined. The reader is also referred to laboratory text books such as reference [2]. In the past, systems have been developed to classify soils based on their particle size distribution and their Atterberg limits. The best known classification systems are the AASHTO and USCS classification system. Since both systems are widely used to classify soils and granular materials, some attention will be paid to them hereafter. AASHTO Soil Classification System: The AASHTO system is developed by the Association of American State Highway and Transportation Officials. This implies that this system and in particular the boundaries that are used, are especially developed for road purposes. The system contains seven classes to identify soils and granular materials. The groups range from A-1 to A-7. Materials belonging to groups A-1 to A-3 are coarse grained materials while materials belonging to groups A-4 to A-7 are fine grained materials. The A-1 and A-2 groups have a sub-rating which will be explained hereafter. A material is rated as a coarse material (A-1, A-2, or A-3) if less than 35% passes the no. 200 sieve. The classification proceeds then as follows. The material is an A-1 material if: Less than 25% passes the no. 200 sieve and less than 50% passes the no. 40 sieve. However if: Less than 15% passes the no. 200 sieve and less than 30% passes the no. 40 sieve and less than 50% passes the no. 10 sieve and PI 6, then the material is rated as an A-1-a material. If less than 25% passes the no. 200 sieve and less than 50% passes the no. 40 sieve and PI 6, then the material is rated as an A-1-b material. If the material is rated as a coarse material but not as an A-1 material, then it is either an A-2 or A-3 material. The next step is to determine whether it is an A-3 material or not. It is an A-3 material if: Less than 10% passes the no. 200 sieve and more than 50% passes the no. 40 sieve and the material is non plastic. If the material is rated as a coarse material but not as an A-1 or an A-3 material, then it is an A-2 material. It might then be rated as an A-2-4, A-2-5, A-2-6 or an A-2-7 material. This depends on the plasticity limits of the material passing the no. 40 sieve. For this the plasticity chart shown in figure 7 is used
704A-7A-6PI[%] 10A-4A-50040LL [%]100Figure7PlasticitychartbelongingtotheAASHTOclassificationsystem.Ifmorethan35%of themasspasses theno.200sieve,thenthematerial is ratedasa finegrained material. The classification, A-4, A-5, A-6 or A-7 is then made based on the plasticitydata obtained on the material passing the no.40 sieve.Because soils withaveryhighLL could notbeclassifiedaccurate enoughbymeans of thesystem described above, a Group Index was developed.The Group Index (GI) is calculatedby:GI =0.2a+0.005a c+ 0.1 bdthat portion of the minus no. 200 sieve greater than 35% and not exceedingWhere: a =75%(soavariesbetween0and40),b=that portion of the minus no.200 sieve greater than 15% and not exceeding55%(sobvariesbetween0and40),C=thatportionoftheliquidlimitgreaterthan40andnotexceeding60%(soCvariesbetween0and 20),d=thatportionof thePI greaterthan 10 and not exceeding30 (so d variesbetween0and20)Knowing this, one can derive that the Group Index varies between 0 and 20. The followingclassificationisgiventotheGroupIndex(GI)values.GIRating0excellent0-1good2-4fair5-9poor10-20very poorA classification of A-6 (18) means that one is dealing with an A-6 soil with a GI of 18. Itshould be noted that if the upperlimits fora,b, C,and d are not used, GI values much higherthan 20can be obtained.10
10 Figure 7 Plasticity chart belonging to the AASHTO classification system. If more than 35% of the mass passes the no. 200 sieve, then the material is rated as a fine grained material. The classification, A-4, A-5, A-6 or A-7 is then made based on the plasticity data obtained on the material passing the no. 40 sieve. Because soils with a very high LL could not be classified accurate enough by means of the system described above, a Group Index was developed. The Group Index (GI) is calculated by: GI = 0.2 a + 0.005 a c + 0.1 b d Where: a = that portion of the minus no. 200 sieve greater than 35% and not exceeding 75% (so a varies between 0 and 40), b = that portion of the minus no. 200 sieve greater than 15% and not exceeding 55% (so b varies between 0 and 40), c = that portion of the liquid limit greater than 40 and not exceeding 60% (so c varies between 0 and 20), d = that portion of the PI greater than 10 and not exceeding 30 (so d varies between 0 and 20). Knowing this, one can derive that the Group Index varies between 0 and 20. The following classification is given to the Group Index (GI) values. GI Rating 0 excellent 0 – 1 good 2 – 4 fair 5 – 9 poor 10 – 20 very poor A classification of A-6 (18) means that one is dealing with an A-6 soil with a GI of 18. It should be noted that if the upper limits for a, b, c, and d are not used, GI values much higher than 20 can be obtained. 0 40 LL [%] 100 70 PI [%] 10 0 A-4 A-6 A-7 A-5
UnifiedSoilClassificationSystem(UScS)Thisparticularsystem isdevelopedforagricultural purposesbut isalso widelyused inroadengineering.In this system, first of all it is determined whether the soil is highly organic ornot. This is done by determining whether the soil has a fibrous texture, a colour or an odourwhether it has a very high moisture content and whether or not the particles aremade ofvegetablelikematerial.Also in this system it is determined whether or not the material is a fine or coarse grainedmaterial.It is a coarse grained material if ≤ 50% of the mass is passing the no. 200 sieve.The coarse grained materials are then divided into gravel (G) and sand (S). If ≥ 50% isretained on the no.4 sieve (4.76 mm)then the coarse grained material is rated as a gravel(G). In the other case it is rated as a sand (S).Next it is determined whether the sand or gravel is well graded (W) or poor graded (P). Forthis the uniformity (U)and curvature index (C.)are used.GravelSandIndex≥4≥6U=D60/D101-31-3Cc = (D30) / (D6o D10)RatingwellgradedGWwell gradedSWThis means that coarse grained materials are rated using GW or GP or SW or SP.Thefinegrained materialsareclassifiedaccordingtotheplasticitychartshown infigure8.10xapul60ose2050403020cSP10MISCMI00102030406070809010050Liquid limitFigure8 USCSplasticitychart.Thedifferencesbetweenbothsystemsaredistinct.Theparticlesizeboundaryusedtodecidewhether or not a material is coarse or finegrained, is rather large in the UScS system.TheAASHTOsystemdoesn'tallowto indicatewhetherornotthematerial iswell graded ornotwhile the UsC system doesn't allow to identify highly plastic soils.The latter is possible in theAASHTOsystembymeansof theGroupIndex.All this indicatesthatoneneedstobeprecisewhen one uses e.g. terminology like"coarse grained" because such an identification stronglydepends on the definitions of the classification system used.Table4givestherelationsthathavebeendevelopedbetweentheUscSclassificationsandanumber of engineering values.It needs not to be emphasized that this information is onlyindicativeand should only beused to get some information on the suitability of the materialto be used.11
11 Unified Soil Classification System (USCS): This particular system is developed for agricultural purposes but is also widely used in road engineering. In this system, first of all it is determined whether the soil is highly organic or not. This is done by determining whether the soil has a fibrous texture, a colour or an odour, whether it has a very high moisture content and whether or not the particles are made of vegetable like material. Also in this system it is determined whether or not the material is a fine or coarse grained material. It is a coarse grained material if 50% of the mass is passing the no. 200 sieve. The coarse grained materials are then divided into gravel (G) and sand (S). If 50% is retained on the no. 4 sieve (4.76 mm) then the coarse grained material is rated as a gravel (G). In the other case it is rated as a sand (S). Next it is determined whether the sand or gravel is well graded (W) or poor graded (P). For this the uniformity (U) and curvature index (Cc) are used. Index Gravel Sand U = D60 / D10 4 6 Cc = (D30) 2 / (D60 D10) 1 – 3 1 – 3 Rating well graded GW well graded SW This means that coarse grained materials are rated using GW or GP or SW or SP. The fine grained materials are classified according to the plasticity chart shown in figure 8. Figure 8 USCS plasticity chart. The differences between both systems are distinct. The particle size boundary used to decide whether or not a material is coarse or fine grained, is rather large in the USCS system. The AASHTO system doesn’t allow to indicate whether or not the material is well graded or not while the USC system doesn’t allow to identify highly plastic soils. The latter is possible in the AASHTO system by means of the Group Index. All this indicates that one needs to be precise when one uses e.g. terminology like “coarse grained” because such an identification strongly depends on the definitions of the classification system used. Table 4 gives the relations that have been developed between the USCS classifications and a number of engineering values. It needs not to be emphasized that this information is only indicative and should only be used to get some information on the suitability of the material to be used