An investigation of the relation of dielectricproperties to plasticity characteristics of soils

Item Type text; Thesis-Reproduction (electronic)

Authors Angemeer, James, 1934-

Publisher The University of Arizona.

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AN INVESTIGATION OF THE RELATION OF DIELECTRIC PROPERTIES TO PLASTICITY CHARACTERISTICS OF SOILS

byJanies Angemeer

A Thesis Submitted to the Faculty of theDEPARTMENT OF CIVIL ENGINEERING.

In Partial Fulfillment of the Requirements For the Degree ofMASTER OF SCIENCE

Tn" the Graduate CollegeUNIVERSITY OF ARIZONA

1 9 6 2

STATEMENT BY AUTHOR

This thesis has been submitted in partial ful-o fillment of requirements for an advanced degree at the*

' University of Arizona and is deposited, in the University. Library to be made available to borrowers under rules of the Libraryo

Brief quotations from this thesis are allowable without special permission, provided that accurate acknowl­edgment ;of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in their judgment the proposed use of the material is in the interests of scholarship. In all other instances5 however, permission must be obtained from the author.

APPROVAL BY THESIS DIRECTOR

This thesis has been approved on the date shown below:

sg A ^ / / f S M Date" ~gcbfessor of Civil Engineering

if

: ACMOMOTEENT • .

The authpr expresses his appreciation to Professor R. L. Sloane under whosepatlent guidance and advice this paper was prepared. ^

ill

... , TABLE OP CONSENTS . • \^

::o m p T # ^ : v' . v: > : „ : . ..; . / .;, v. ■ ■ ;i ' .: -''

1.1 Plasticity and Consistency . . . . . . . . 1 •: : " 1.2 ' Atterberg Limits. . o -. .v’. . . »■ . . . . •> ' , - 2 ^

1.3 ' Review of Mterature. <i . * .; . . . 41.4 Pbyslc^l and Electrical Properties of .; ':;l Clays Related . . : .v i; 4 : . . ■ , 5 "

4 41..5;- Dielectric Properties Def ined ' . . 4>‘ 1-4- "8• 1.6 Dielectric Behavior . : . v . . . . . . . 9

CHAPTER 2 THE # ., 4 ,. . , . j... 4 ■ ;' . 12' ..c ;• 2.1 General . . .. .4' 4 ' , 124-:4'

2.2 Soil Praction Used 4 . 4 . . . 122.2.1 Meedlfor RepresentatiyevSaJi^les 4 .4... 13 ■ ..2.2.2 Elimination of Moisture Effects . . .132.3 Dielectrie. Measuring Equipment . . . . . . 14 4/

■ ,4:: 2!.3 .'lt .8 . ... ;4 4 . 4 4 4 4 - .4. ■■ v4>: -t 142.3.2 Sample Requirements . . .. . .. . . . . . . 142.4 Dielectric Specimen Fdrrning . . . ! . . 1 5

CHAPTER 3 EQUIPMENT ^ . l6/- '4i■ 3.1 Sample Preparation . . . . . . ..... . . • . 3, - 16 -

. 3^ 2< .: ; Molding: Equipment and Technique 44. 4 • 17' 4 34241 Pellet Handling After Molding . . .4; . . . 17

iy

Page3«3 Dielectric Measuring Equipment and

Technique „ » « , . < , . , .. . . . . . . » 18.3-4 Standard Dielectric Pellet . .■ . . „ . 193-5 Weighing Equipment . . « . . . . . 193-6 Magnetite Removal Equipment „ „ » - „ . 203-7 Consistency Limits Equipment . . „ . . „ » 203-8 Grain Size Determination Equipment „ „ „ . 21

CHAPTER 4 SOIL SAMPLES „ 4; „ \ . . . . . , . 224.1 General . . . . . . . . . . . . . . . . . 224.2 Composition . - . . . . . . . . . . . . » 224.3 v Consistency Limits . . . . . . . . . . . . 234.4 Grain Size Distribution . . . . . . . . . 23

CHAPTER 5 TEST PROCEDURES . . . . . . . . . . . . . 245-1 Sample Preparation . . . . . . . . . . . . 245.2 Dielectric Pellet Forming . . .... . . » - : 255-3 Hygroscopic Moisture .Control . . „ . . . . 265-4 Dielectric Measurement . . . . . . . . . . 275-5 Calculation of Dielectric Constant . . . . 285-6 Second Series Tests - Magnetite Removed . 325-7 Consistency Limits Tests and Grain Size

Analyses . . . . . . . . . . . . . . . . . 32CHAPTER 6 DISCUSSION OF.RESULTS .. . . . . . . . . 36

6.1 Accuracy of Plasticity Index Evaluations . 366.2.) Accuracy of^Diele'ctric Measuring Equipment . 36 .

v

. : /: - , : : ^ : : . 7 ; ; \ ,{ ^'% -\ - P^ge6.3 ; • : Soil Pellet Reproducibility . . „ . ^ . 37 . •

: - 6.4 -v- Dielectric Constant of Natural Soil ; . ; - 38 , . ■ '•C :v 6v5 . Dielectric Constant of Soil With : . :. ' ■ : t i; ' i Magnetite Removed . „ . • 4 v .. 38 a ' ,

\ Influence of Grain Size . _ » ° » : v . 39 .■ ^ . /: 6 »7 ; /r:: Mettiod, of Curve Pitting . 7 » i. . ’ . V / : ; 40 .

: 3 CHAPTER 7 CONCLUSIONS . I.:' 7 v.7; 7 7; . ;.7 i .. 3 42 ; ■ ■ . ;7.1 Dielectric Measurement Procedure Developed 42

:v; 7.2 Hygroscopic .Moisture Control ‘ . . 7 .' . . .. .7 7- 42 ". 1 7«3 ■ Effect of Magnetite 7 .7. .: 7 :3 . .7 7 . 4 3rr ( 77 7.4 , 7 Inflnence of Particle Size:'. . « 7 7 . » ; ; 43

7.5 Need for Additional Research' . '. *7, 45 ' :7' 7' ® 773.;.'. .7 ■•'7:7 7; 7 7 •: » 7 ,7S ' 46 •

■■ 8.1 7;,General ' . 7 . :.;'7 . 3 '.7 3./33 ; « • . . . v 46 .7.-';

7 8.2 7 7 Need for Control of "Variables . > . . <, . 467 7 777'7 7 8.3 7AvCnue ,of Research . 3 7 . . . . . = . . . 477 '77 APPENDIX ; :' 7:;7i'•77:: 7', 77;'. - 7/> 7rf'77T • 7 ’ 7 '' ; ; 7 • '

. :77 7 '7'. A Grain Size Distribution Curves , . . 7, 7. ;3- 48 7'. 3 ,37777■■ 77 B 3, ' Tabulated Data 7 . .. v .. . . . ► 63 . .. ■

: : :..SELECTED EEPERENCES» 7. i . 7 3 .: 3: 7 . . 3.3 7: 7 7 66 .7.7 ■

' LIST OF FIGURES

5.1 Dielectrie Constant/: • of Pellet versus PI^stieTiy Index p&tural Soil)5.2 . Dielectric Constant of Solids versus

. Plasticity Index (Natural Soil) ? „5.3 Dielectric Constant of Pellet versusPlasticity Index (Magnetite Removed) .5,4. • • Dielectric .Constant of Solids versus

Plasticity Index (Magnetite Removed) . .6.1 v: Dielectric Constant of Solids versus

. ' Plasticity Index (Magnetite Removed)13 +1$^ -5 'mldrdn material . i'.l ’ .

6.2 .. Dielectric Constant of Solids versusPlasticity Index (Magnetite Removed)13 ±2%s -5 micron material \ .

,6*3 Dielectnic Constant of Solids versusPlasticity Index (Magnetite Removed)

; 13 +3$, ~5 micron material . . * .. . .. .6.4 :/ pielectric-Constant of Solids versus

,. Plasticity Index (Magnetite.Removed) V/ Vi 13 *4^, : -5 .micron material . : . .1' v- .i.'

via

Page yi.;'::

- .30 ■

v.::' :'34;':

35 '/ ’;i

* / I V' 41' : ly ;

' ■ Chapter'1 ■ , ';':: . , ' , INTRODUCTION.

: 1.1 Plasticity and ConsistencyiPlastleltsr may be defined as the ability to undergo

changes pf shape without rupture; This general definition, as associated.with soils, is primarily related to the finer soils or the fine fraction of coarse soils. Different Soils, .show different plasticity characteristics according to the amount and ;kind of clayorclay-size particles they contain and the inherent moisture conditions 1 ‘

< Plasticity is frequently.associated with consistency.Consistency is. the degree of resistance of a fine-grained ,

■ soil to flow or deform... It is obvious that> in soils, both are markedly affected by changes in moisture content.

: pbn&istency denotes a degree of firmness of soil and.is Indicated by such terms as soft, firm, or hard. As a soil changes .consistency, its engineering properties also change; fOr example, shearing strength varies significantly with . .

n v consistency. Since consistency varies in part with water ' content, it is possible In Some instances to use water con- tent as an index\of consistency. However, it has been found that at the same;water content, one soil may be relatively

I

; .. ... ■ , ■ ' ‘ .. 2 soft wjb.ile a different one may be hard-j a change in water .content may have very little effect on one, while it maytransform the other from a firm to soft or liquid condition.Water content alone is not an adequate index of consistencyfor engineering purposes.

1.2 Atterberg Limits , ' ' 'In recognition of the inadequacy of utilizing water

content alone, Atterberg combined consistency, degree of resistance to deformation, and plasticity, into a stand­ardized system for better engineering appraisal of fine­grained soils. In 1911 and 1912 Atterberg (l, 2) studied the plasticity of soils on the basis of moisture range over which plasticity was evident. He established three moisture values, which-can be obtained by routine empirical testsemploying a fixed or standard degree of energy input, thusestablishing the degree of resistance to deformation, con­sistency, and utilizing plasticity since no rupture occurs. These moisture values are as follows:

(1) The liquid limit, or that moisture content at which the soil will flow when jarred

: ; ; -./lightly, ' ; , ■ - .•■ : .(2) The plastic limit, or that moisture content

at which the soil can barely be rolled to a- 1/8 inch diameter thread.

The plasticity index . or the difference . v in moisture content between the liquid and plastic limits a.nd defines the range

■ ' . Of, moisture . content over which the soilis plastic in bdhavior. - ’

It should be noted that the Atterberg Limits testsdo not measure the individual effects of the clay-size particles or the clay minerals comprising the soil fines„Ihe; .tests determine the Statistical average; of 'the effects ;• of the clay minerals or clay-size particles present. Both Atterberg and Terzaghi (23) Showed that■an increased amount of clay causes; both plasticity limits to be raised and also ; increases, the plasticity index. Others have demonstrated the effects of particle Size on plasticity. '■ 'vi The Atterberg limits reflect several properties ofa soil which are vital in engineering work. A soil, having amoisture .content between the plastic and liquid limits will deform plastioally U T^ ease, with which It will. deform will. increase as the actual moisture content increases from the plastic limit to that of the liquid limit. If the field moistUfcevj content is below the; plastic limit> a soil will exhibit properties approaching those of a semi-elastic solid. These and other important soil properties are affected by the type Of clay mineral In the soil and other, physical factors reflected by the Atterberg limits. Since these limits are

e l d s e d 60 field soil properties. It is notsurprising that the.routine empirical tests for their deter- rainatlon have attained^widespread'use. ; . ■

: ■•Such; tests, however, are subject to certain inherent : inaccuracies, not the least of which is human error. The •' plastic limit,: in particular, is much affected by both the experience and judgment of the operator. In addition, both the liquid and,plastic limit tests are time consuming. Since a great number of plasticity evaluations are required continu­ally in the construc tion industry, it is apparent . that much :' time could be Saved if'quicker and more positive test methods , - were developed. The possibility that another method could be . developed. for predicting the plastic behavior of soils on /Some other basis was the motiyation for this project. "■';::.v : i

1.3 Review of Literature•' • ' In the extensive review of the literature only onearticle by Fletcher■(ll), in connection with his research on soil moisture by dielectric methods, in which he stated, "Apparently the amount of colloid does increase the dielectric constant .of soils but this will have to ,be investigated in : , greater detail," Contributed' directly to. the problem.; ;, . ■ It was found that the utilization. ■ of. dielectric con­

stant for moisture deteasnihatlon in materials from soil to ■ 'bread flour has been attempted. The correlation or association

of die1ectrie constant with mineralogical make-up had not been attempted^" ; .

There is considerable literature discussing soil plasticity;and numerpus discusslpns'of factors affecting soil plasticity^ but a basic theoretical explanation has. not yet been developed. The approach utilizing charge Imbalance of the crystalline structure of the clay minerals ■ as an explanation has not been found in the literature:, yet this appears to be a logical beginning for development of an explanation leading to fundamental understanding. -

1.4 Physical and Electrical Properties of Clays Related: - Significant differences in.plasticity; are exhibited

by different tyjpes: of clays. Most .clays of the montmoril-' . ’ Ionite type showing a .high affinity for water will expand . . considerably and act as effective lubricants when wet.' By " contrast, kaolinite clay.geperally has a much lower capacity for water and tends' to retain a greater frictional resistance IIlite clays appear to be intermediate in properties when. y ; compared to the other two'play classes. The differences, in the affinity of clays for water are attributed to the atomic ’structure of the clay -mineral predomihating in the clay soil. The most common and abundant•clay minerals in natural.soils are kaolinitej montmorilIonite and illite„ : .' Kaolinite clay consists of a sheet composed of onesillcon-oxygen 'Unit and one aluminum-hydroxyl-oxygen unit.

;::These /am- the silicate and gibbsite sheets respectively . The ■: Silica sheet or silicon-oxygeh imit is kade Up of silica tetrahedra. In each tetrahedron a silicon ion is equidistant . from four oxygens or hydroxyls, arranged in the form of a tetrahedron with a silicon ion at the center, The tetrahedra are arranged in groups to form a plane hexagonal network with the tip of each tetrahedron pointing in the same direction.The gibbsite or aluminum-hydroxyl --oxygen unit consists of two Sheets'df closely packed oxygen or hydroxyl ions in which • aluminum ions are embedded in two-thirds of the possible ■ octahedral coordination positions so that, they; are equidls- -: i tanf from six oxygeh or jhydrox^l' ions h - .

In the kaolinite structure the unit is in electrical v equilibrium except for unsatisfied bonds existing along edges'' Of sheets. In the'mineral - the silica and.gibbsite layers occur alternately:Se' that there is; an attraction between the adjacent oxygen laydr of the silicon-oxygen unitand the y ; • ■ hydroxyl ions in ythe gibbsite: layer leading to hydrogen bond ' stacking of the electrically neutral units, There is little cation substitution occurring naturally in the sheet struc- ,turei: The predominant attraction of cations and. water dipOles is to the edges of the sheets where unsatisfied valence bonds

. exists thus the minimum or small amount -required, ;i "

. The montmorillonlte unit cell is made up of two- silicon-oxygen sheets sandwiching one aluminum-hydroxyl- v Oxygen sheet. * ideally>, this - w has electrical neutrality

soils alwinum and silicon ions are usually partially replaced by other ions oi similar size but differ­ent charge re suiting in an over-all electrical charge irabal-' , a n c o :"■This, in addition to the fact that in mass buildup the adjoining sheet interfaces are composed of oxygen layers ■ 'which have little affinity for each othery.contributes to an unstable structure and ;the high affinity for water. The low order yah der Waals forces which tend to prevent layer separa­tion •Initially are of Insufflolent magnitude to maintain close stacking in the presehce pf water dipoles and'/ cations; The 'C1ay mineral unit wil1 strongly attract cations and water , dipoles to satisfy the charge imbalances in the sheets and ■thesewill overcome the Van der waals forces and intrude intothe interplanar positlohs in addition to the sheet edgesV Ifi...;: 'V yh"'; .i' w : & :;this action is unimpeded until equilibrium IS reached, the •structure wlli swhli- cdnsiderabiy and external faces andedges will adsorb thick layers of moisturev : -

' Illlte IS: intermediate between kaollnite and mortmo-rillonlte in its affinity for water. The structure of illlteis intermediate between kaollnite a%d mortmoriilonite instabiiity but is structurally more like a montmorillonite andresembles the flexible micas. « The natural cation substitu- •;tlon and electrical Imbalance associated with montmorilloniteis partly balanced by'Interplanar petassium ions linking the.oxygen atoms at v the. inter if ace In illlte, thus the more stablestructure. ' ' . ■■ :

v . It is evident from, the above discussion that indi­vidual structures are present in each of the common clay min­erals '.present in natural soils. These structures have dif- • ferent arrangements' of "Bonded ions and .thus a difference in polarity. •The polarity of each; or the lack of coincidence of. the ".center of gravity" of the protons and electrons of each structure; should be a diagnostic feature for identifi- cation purposes. This is substantiated by Debye (7) who ; postulated that the'"molecules of substances in which charges are not symmetrically arranged possess an electric moment, which is characteristic of the molecule", and this may be measured by a simple electrical bridge unit.

1.5 Dielectric Properties Defined v ■ :' ; Dielectric "constant", is not a constant at all,in then

usual physical meaning of the word. It is a property which depends ph.. such - variables' as- temperature and' electric in ten- .. sity. Pundamentally> it is the ratio of the average electri­cal charge displacement per unit area in a body to the elec­trical stress displacing it. 'Mathematically this is expressed

; Cvr- - KKv E : ^ t ■ V,:>:. ^ ..'where : D is 'tbe;,vectbr. electr'lc .displacement,:; B is the vector electric field, K is the relative dielectric constant and Ev is the permittivity of a vacuum..

-:Ifc is more common to find dielectric constant defined in terms of a parallel-plate capacitor. According, to this

definition, the dielectric constant of a material is the ratio of the capacitance, C, of the capacitor with the mate­rial between the plates to the capacitance, C0, of a similar capacitor in vacuo

where the charge on the plates and the voltage between them are q and V with the material present, and qQ and VQ in vacuo.

The amount of charge which will exist on a pair of plates held at a given potential with respect to each other depends on the nature of the material between the plates.The dielectric constant of a material is equal to the ratio of the charge which will be present with the material between the plates to the charge which will be present in vacuo.Thus, the larger the dielectric constant of the material, the larger the charge which will be present.

1.6 Dielectric BehaviorWhen an electric potential is applied to a capacitor,

the electrons flow from one parallel plate to the other.This flow leaves one plate lacking electrons, thus positively charged, and the other with an excess of electrons, thus negatively charged. The flow of electrons will be through the electrical circuit connecting the two plates, and will stop because of the pile-up of charge on each plate opposing further transfer. The higher the voltage applied to the plates the greater the charge that will build up on them.

q/VW V o

The capacitance of the .capacitor is defined as the ratio of the charge built up on eitheh'plate to the applied voltage =

If a charged particle is inserted between the plates : of the charged capaoltdrjtlt is Aubdpoted to an electric field. ,This field exhibits a force•on the particle which draws it tb the oppositely charged plate„ If a polar par- : ticle is inserted, it will tend to align itself with its axis in the direction of the field with unlike poles of the capacitor and particle exerting force on each other. The. particle will move to the’ charged plate of the capacitor if restraint is not applied and will partially neutralize the charge on the plate. The partial neutralization of one ; v plate:permits an additional electron flow in the circuit to re-establish equilibrium for a given voltage. .

When a polar crystalline1 material is placed in the electric field of a capacitor, the electrons ofthe material : are not free to move at will although they are acted ■' upon by . the force of the induced electric field. Since the material is polar and the centers df the positive and negative charges do not coincide, there is a preferential alignment induced. The positive center tends toward the negative plate and the negative toward the positive plate, thus causing a moment.The ‘mpment; is called the dipole moment and is a-measure of the polarity of - the material. The moment is resisted in the material by the internal.bonding forces and these bonding • forces retain the idn.cbffiguratloh but in a strained ’ v'

11condition. The restoring forces vary in different materials as does the polarity3 thus there is a differentiation in displacement or strains induced by any given electrical field.

With the difference in internal restoring forces and polarity in material affecting the strains induced in the ions by the electric field of a capacitor, a distinction between materials is possible through the variations in the capacity of a capacitor. The variations in capacitance are exhibited because of the differential neutralization of charge on the capacitor plates by the polar ions. A greater dipole moment permits more charge neutralization and thus greater capacitance for the capacitor. An index of the ability of a material to change the capacitance of a capaci­tor is known as the dielectric constant. It is defined as the ratio of the capacitance with a material insulating the plates to the eapacitance with only air or vacuum between the plates. '

. : ' - Chapter 2 /' " THE RESEARCH OUTLINED ; ' '

2.1 General ' ,It has been shown In. Chapter 1 that it is reasonable

to expect the electrical' properties of the soil to be Indlc- ■a.tlve of Its ph^sleal" behavior J • Since the dielectric con­stant is an ■ electricaliproperty of the material,: it should illustrate a relationship between the electrical properties and plasticity. Since this was an apparently new approach to evaluation of plasticity,, it- was decided, to adapt tech- ' nidues as near to standard methods wherever possible.

.Soil Fraction Used, . ' ■ ; •In the study of plasticity conducted by Atterbergi;

it was determined that the coarse-grained fraction of the , soil does not contribute to plasticity. Since the fine-

: grained fraction of the soil was found to influence plas­ticity while the coarse fraction did not> a‘ division of the. - twp fractidns must be accomplished . A11erberg used as the ■ • ,fine fraction the minus NoP 40 sieve sizes, therefore, thesamples utilized in. the pro ject consisted of only that mate- , rial passing the, No.. 40 sieve. It was felt that if a corre- lation between dielectric constant and consistency limits

12

^: V;:;;:. ^ ^ :/;% ^ - ; ' : *- \ x,.. - : 13existed> 11; would be more readily distinguished using the same size fraction.

2.2.1 Need for Representative Samples. '.: V : Plasticity determinations by the standard method ■ : ■,require 150-200 grams of minus No. 40 material that is rep­resentative of the soil sample. In order to obtain an ..equivalent hepresentatuve' sa^le fOr dielectric determlna- I : tions^ care in sample splitting was necessary since dnly four , grams of material Wquld he • ■utilized. Because such ^ ■

small portion,would represent the entire sample, as compared to the approximately two hundred grams used 'in consistency limit determinations, it was■decided that precision sample splitting wonld be utilized in order to get as truly repre­sentative a sample as possible fOr dielectric determinations.

2.2.2 Elimination of Moisture,Effects . - n; ’ . Knowing that • the dielectric constant of most soil i;;constituents lies in Cthe rang® Of values from 4 to 10, and that of'Water is 88/ it was decided to eliminate the water by oven-drying samples to avoid gross changes in true die­lectric constant. Since the Contribution of water in the .dielectric measurement could hob be separated; from the total •: measurements the oven-dry sample would permit a determination of the dielectric constant for the material directly. .-; /llli

2 „ 3 Dielectric' Measuring Equipment .■ : v;; ' Dielectric measurements were made on equipment avail - .

able- in the Department of Civil Engineering. This equipment -consisted of a basic bridge arrangement with a variable fre- : ,

, ■ quency signal and a sample holder: arranged, as a component of : :: .1,the bridge circuit. -.' I .

2.3«1 ■ Sample Holder - . • 'The sample hblder consisted of two precision ground

electrodes with an adjustable gap. The electrodes and sample v ■ holder constituted a capacitor arrangement5 the sample acting " t':

: as an insulator or conductor between the electrodes. The 'oohtact^ thickness, and diameter of sample between the elec- •

■ trodeS must, be obtained in. order to know the distribution of field necessary for dielectric determination, • The thickness

. . of the sample was indicated directly by the spacing of the electrodes of the holder but the. contact and.diameter were

2.3.2 Sample Requirements • - : t• The geometry of the sample holder fixed the basic ' .

' requirements for the dielectric:;,sample' In order to eliml -■ . :;,;yhate fringe effects in the holder, the sample had to be less : than two inches in diameter,and one hundred to two hundred • : 1.

; . ’ til is tbLic k. : - To j e s t ab li sit a knoTma f I e Id across the sample,the contact area had to be known which required the sample ' . to have, plane, smooth surfaces.: Another'requirement was • •. .

. r : : y ^ ;;.. 15 ;that the sample had. to be coherent« . This was necessary because a .uniform pressure was'applied•when the plane-surface electrodes came into contact with the sample. •The sample must not be distorted or changed during testing because of the contact, thickness, and size requirements previously mentioned. • : :iy, ■ ;; •

2.4 , • Dielectric Specimen Forming '•The method decided upon to impart the necessary char­

acteristics to the soil sample was to form a coherent soil pellet:in a specimen molding press„ " An adequate quantity of oven-dry soil fines was placed.in the die of the press and formed into a coherent pellet with plane surfaces, one inch : in'diameter, ■and between one hundred fifty and two hundred . .• mils in .th.ickness.;: V

Chapter 3 . ■ -’ ' • • , ; : ' EQUIPMENT : • •

3.1 ^pmplp .Prepara^tlopy ■ ‘V /■:' V;,.: ■■■ -.'3 : ,In preparatlori/ the gross soil sample was split by

a 32-chntei 93 cubic inch, Carpco precision sample splitter. This unit was used to reduce the size of the sample to that necess.apy for consistency limits > grain size> and specific grayity determihations« . ' ' • ' ;

Further reduction in -sample size was accomplished by a 16-chute5 8 cubic inch, Carpco precision sample splitter. -The small 1/8 inch openings of this unit.provided a .greater . number of divisions and thus eliminated the possibility of punching or uneven distribution in the sample Splitting.The amount of material for the soil dielectric pellets was split down in this manner to. insure mthe same sample. The.material for "the specific gravity and grain size determinations was further split down with this equipment to insure true representation of the total soil

Va.:/.- : : V / • ' V . / / / n - 'Drying of the samples was accomplished in a Cenco,

. grayity-convectidn, drying oven at 1C5V degrees Centigrade . This unit was used" only for this pioject. Cooling and

moisture control were accomplished using desiccators and anhydrous calcium, chloride desiccahtV

3.2 'Molding Eauipitdnt and W r . :'' .With the dielectric samples in a fine-grained, loose

State, it was nebessary to: produce coherent, pellets for :' :. .dielecthic determination. This waS accomplished by using - a;Buehler specimen mounting press.; The press consisted of ■ a loading frame,:capable of 15,000 pounds per square inch loading, and a precision die one ;inch in diameter . The die ' unit was very precisely machined and lapped. The ■ die1ebtrie sample was placed loose in this unit and compressed by the hydraulic system of the loading"frame,under a constant 6,000 pounds per square inch pressure. The load-was maintained / for three minutes:and then released. The pellet, thus formed, was ejected from the die by a plunger system incorporated in Hhe-Ibading frame and designed for this purpose.

3.2.1 y Pellet Handling After Molding ‘ - ■" Ejection.of the soil pellet from the die and placing ;i it-into the container without breaking the edges posed a problem in pellet handling. This was:satisfactorily solved by utilization of a plastic stage.. The pellet was ejected tfrom the .•specimen molding /die: with: W plastic stage held in close contact. When the pellet was free of the die, it was . resting :mif©rmiy onrt^ This technique and ■unit proved satisfactory and 'eliminated almost all disturbance

. 18of the soil pellet. The plastic stage also enabled the pellets to be put into, and removed from, the air-tight glass containers in which they were kept and transported.

3.3 Dielectric Measuring Equipment and TechniqueThe sample holder. General Radio Model 169O-A, acted

as a parallel plate capacitor. This unit, utilizing circu­lar plate electrodes, enabled the distribution of field to be known. With pellets from 130 to 180 mils thick, fringe effects were eliminated. The precision-ground electrodes were adjusted by an accurate micrometer screw which drives the movable electrode with respect to the fixed one. A release mechanism in the unit permitted accurate determina­tion of the pellet thickness when the electrodes were in intimate contact with the pellet surfaces.

A General Radio Model 1610-A Capacitance Measuring Assembly formed the circuit in which the 169O-A Sample Holder was an integral part. A constant signal of 50 Kc was utilized throughout the project.

The signal was generated by a Type 1302-A Oscillator and R-C Oscillator, with a frequency range from 10 cycles to 100 Kc, employing a Wein bridge circuit in the feedback path of a two-stage amplifier. A type 1231-P5 Filter, consisting of a group of high-Q, parallel resonant circuits, and a Type 1231-B Amplifier and Null Detector, consisting of a combina­tion- high gain amplifier and sensitive null detector, combined

' . '"'\V' . " ' ; ' / v';■:y ■' : ;r - ; ■ 19' with the Type 716-C Capacita.tice Bridge, Sobering Bridge, and Modei;l6lO^A Sample Hplder formed the;complete qircuit.

' The bridge was balanced Tor both capacitance and • resistance losses:, witb only the capacitance readings being recorded. .. In' measuring values of capacitance which fell beyond, the limit of the. standard bridge -balancing capacitors of 1,000 uut, a variable external .capacitor was introduced into the system. '■ • ' : ,

- 3-4 Standard Dielectric Pellet V ' ' ' ' ' y

iV'taTo .pheclc the reproducibility and act as a constant check on measurements by the equipment, an acrylic resin pellet was formed/ of the same dimensions as: the soil pellets „ The plastic.-pellet was itaintained in a desiccator except . during measurements. The values of dielectric;constant for the Standard,varied from 2.60 to 2.64 throughout:the project,

' measureWnt being made before, during, and after soil pellet - measdrements. The reproducibility of measurement by the equipment was very good, ■Variation in: soil pellet measure- 7

, ment for the same sample was attributed t6 differences within the soil pellets> /--:n. . . ■ /,/t , ’

3.5 / Weighing: Equipment - . % ' , ■ ■ : ;/:. / - ; ■ ■ ■■:' The weighing pperatidns necessary for this project

.were Conducted to/ 0.01+ grams accuracy. . Weighing was accom- //plished rapidly on an Oil-damped torsion dial' balance; ; / /: /' / ■

, 3 . 6 Magnetite. Bemoval Equipment . . ' , ' ;" . A Garpco induced magnetic roll separator was used •

to . remove the magnetite from the 20-25 gram saraples used In the second series of tests. This unit removed the magnetite rapidiy.:and efficiently •from the; soil samples by an electro­magnet in the flow path of the material it passed over the rolls of the apparatus„'' The.material fell to a divider . and the magaetite was attracted to one side by the magnetic; field. The. magnetite-free material fell, with no influence by the field, and appropriate setting of the divider sepa­rated the magnetite from,the non-magnetic.materlal. The speed of the rolls was>:depeadcnf on the particular material being.divided and.strength:of the field was controlled by setting an. electrical input. Several passes of the material through the unit .eliminated the strongly magnetic materiai frc#: the aample..'' " • '" • ' •

3.7 . Consistency Limits Equipment ;' ■ •' The equipment used in consistehcy limit determina-

tions whs' identical to the Standard equipment shown and described iri American Association of State.Highway Officials Standard Methods,of .Test' T89-49, T90-49, and T91-49, "Deter­mining theLlquid Limit, Plastic Limit, and Plasticity Index

pof'"Soils." ■ ■ ''• ;v ; , : i

:' \ . . \ - . '/v>':,.■ 213.8 Grain Size Determination Equipment

\.;/y arica3i-\A SQc:iationv.of:'State''^ghway.-..OffiQiais .... ’ '/St&dard'-Method.Tfest,. 88-^9^ -’Mechaji'ic.aLl Analysis of ■ Soils3n.lists and illustrates the. equipment used for the grain size deteipinqtions: and,; American Association of State Highway.Officials Standard Method of Test> T100-38s "Specific Gravity of Soil, Illustrates the .equipment utilized In the sped if ic gravity: determinations. v - v;' .

^ ': qh%ter :y . ■;■ .; / v y v 3^1- ''■ /SOIL'SAMPLES ^

/' : ry \"" - : ' ' . ."'' ^Fifty test samples, were received from tiie. Materials

Division : of the Ariso Department , Fight of these '.samples had been utilized by the Highway Department as stand­ards for consistency limits determinations in. the Materials . .Division i ' These samples have been retained for several. years and cOristitute a long-term checlc oh: the reproducibility and continuity of consistency limits determinations, -The remain- ihg; fortjr-two; samples were randomly ‘chosen from naturally occurring soils in Arizona which were investigated in con­junction with pro j.eots conducted by the Materials Division.

The soil- finesj Or minus Ho. 40 fraction^ constituted the entlne . soil samp 1 es received and: investigated, I ; ■ ” ::

4.2 Composition . ,The .coarse-grained fraction -of the samples was com­

posed of quartz and feldspar predominantly, with some heavy minerals,: The fine-grained portion of the samples was com­posed Chiefly of montmorillonites and mixed-layer clays. %eing:: sufface of near surface samples of naturally occurring soils, the samples contained a widely varying amount of ,organic content. ■ ..f f ’ :: ; ' 1 : 1

- 234.3 Consistency Limits

. The consistency limits of the materials varied from non-plastic (NP) to 29 with an average value of 12. The materials generally exhibited a sandy texture and appearance which conveyed the impression of little plasticity. The montmorillonite and mixed-layer clay of the fine fraction of the samples definitely influenced the plasticity. A small percentage variation in clay-size materials which would go undetected in a dry sample, definitely affected the plas­ticity although the dry textural.appearance did not change. This has been known and accepted for some time.

4.4 Grain Size DistributionThe grain size analyses illustrate the particle size

distribution for each sample. The distribution curves illus­trate a predominance of poor grading for the minus No. 40 fraction of the natural soils. Grain size distribution curves are contained in Appendix A.

y:::::,;:;.;:: . »apt=ei--5 ' \ : ■ ; .' ' TEST PROCEDURES : ; ' :

5.1 Sample Preparation ' y , , : /./Each, of the fifty soil samples received, from the.

Arizona Highway Department was split initially by a Carpco precision sample splitter. The 800 to 900 grams of minus No. 40 material of. each sample, was divided so.thatVthe 20 to 25 grams taken was truly representative of the entire sample . This portion. -wa.s then further split by a 16-chute • f Carpco 'precision- sample splitter. Precision sample split­ting resulted in four units of approximately 5 grams each Whiph were truly representative of the original soil sample.;

Initially, , sample preparation was carried to the ■ ;i.point of splitting:a representative sample of 20 to 25 grams and reducing this to the 5-gnam samples, by scooping the appro priate'. amount into containers . This technique was. checked by the precision sample splitting method. The scooping method produced a 2 per . cent .greater variation, in,the die- - t leotrio determination for the same sample than the more ■ ' :

p..preciSe/-.|rie.thptl''''''0:;f' tample-' preparation..The approximate 5-gram, units of each sample were

oven-dried at 105 degrees Centigrade for a minimum of twenty- four hours. The four approximate 5-gram units of each sample

■ were cooled and weighed to 4.00 grains,-' care being exercised-- - > to prevent hygroscopic moisture adsorption. After weighing

the oven-dried material to an accuracy of 0.01+ grams, mois- tiire: oontrol was negleoted until after pellet formation.

V . The utilization,;.of a 4.00 gram sample was arrived - ; ■at after numerous trials of pellet sizes. The 4.00 gram

' ^quantity of soil fines provided enough material for a rigid, : ^durable pellet and one thin enough' to eliminate fringe effects ■

;. and dissipation factor, for . the dielectric sample holder used

5.2 Dielectric Pellet Forming i - » . :1 / ' The'loose 4.00 gram units of each■ soil, sample were , / '

formed into coherent soil pellets,by using- a Buehler speci­men mounting press .* , A minimum of three 4.00 gram coherent :/ + ■<■;

,,soil pellots 'wee formed for each of the forty-five moldable V '■ soil samples. ■ . r. " - - -. +::;

The 4.00 grams of loose soil were placed into the circular mold after a One -inch diameterground and lapped ;; steel plug: had been inserted at the bottom. A one--inch diam- ■

. . eter, ground and lapped piston was inserted at the top and ' - 1extended beyond the top of the mold by an amount equal to the 1-1height of the material inside. The mold, with the 4.00 grams ,•

, . of loose material inside, was then placed into the compression■, ttnif Of compressive stress of 6,000 pounds : + ■

;. v ; per square inch applied. The compression load on the piston - • + :and material was maintained for 3 mihutes after which a '

coherent one-inch diameter^ average 150 mil thick, soil pellet was carefully ejected from the sample mold. The pellet was handled very carefully to avoid deterioration of the edges or plane surfaces. A technique was devised for handling to eliminate deterioration of the pellet. A small plastic stage was evolved after it was found that handling affected capacitance measurements (see section 3.2.1). - ' : / - . '

5.3 Hygroscopic Moisture ControlThe pellets molded for each sample were oven-dried

for twenty-four hours at 105 degrees Centigrade prior to capacitance measurement and dielectric determination. After oven-drying and prior to capacitance measurement, the soil pellets were carefully controlled to prevent moisture adsorp­tion. The oven-dry pellets were cooled in a desiccator while kept in air-tight weighing bottles.

Prior to careful moisture control, the sample pellets were exposed to the atmosphere for some period of time beforethe measurement of capacitance. The variation in measure- .ments on different pellets for the same sample was of the order of 12 per cent. This large deviation was thought ini­tially to be induced by equipment malfunction so a standard acrylic resin pellet was formed. The standard pellet was also exposed to the atmosphere between measurements. The deviation, noted after numerous measurements of the pelletwas only 42 1/2 per cent. This suggested that something

other thae. the equipment was, indue Ing the variation and as a result moisture control was initiated. With the initia­tion of careful moisture control, even on the standard acrylic resin pellet, capacitance measurements were more consistent. The deviation of the capacitance measurements on the standard acrylic resin pellet was less than +0.5 per cent and' that for pellets of the same soil sample was +1.5 per cent after the initiation of moisture control.

After elimination of the moisture variable, the plastic pellet was used as a standard and measurements were made before, during, and after soil pellet measurements.The consistent accuracy of these measurements over the period of data accumulation gave a continuous long-term check on the bridge system and indicated consistency of bridge performance

5.4 Dielectric MeasurementThe capacitance, for a minimum of three oven-dry

pellets, was determined for each of the moldable soil samples Soil pellets were placed between the electrodes of a General Radio Type 169OA Sample Holder. The sample holder indicated the soil pellet thickness directly in mils as well as form­ing a complete bridge circuit with a General Radio Gapaci- tance Measuring Assembly Type l6l0A. The bridge circuit, using 5Q Kc frequency, was balanced by varying the bridge capacitance and observing: an indicative null. After observ­ing the null," the soil pellet was removed from the sample

28holder and an equivalent air capacitance measured. From this, and the sample thickness, the capacitance and dielec­tric constant were computed.

All tests were conducted under atmospheric condi­tions with temperature varying from 20 degrees to 35 degrees Centigrade and relative humidity varying from 3 to 75 per cent.

5.5 Calculation of Dielectric ConstantDielectric constant was computed by the following

CxCm Ax

aE= dielectric constant= capacitance of sample= geometric air capacitance of elec­

trodes at a spacing equal to the thickness of the sample

= area of specimen = area of electrode

The dielectric constant of three or more pellets was determined for each sample. The numerical average was deter­mined from these in order to arrive at the dielectric constant for each of the forty-five moldable soil samples.

The effect of void ratio variation on the dielectric constant was eliminated by the use of the theory of mixtures and the calculation of the absolute dielectric constant for

K

Where: KCx Cm

Ae

29the soil solids. This was accomplished by using the follow­ing relationship:

S iEmix. = E1 1 E2 Yevstigneyev (24)

Where: E = absolute dielectric constantEmj_Xi = dielectric constant of the total mixture

of air and solids

Eie2

S , and5^2

S i

s21

= absolute dielectric constant of solids

= absolute dielectric constant of air

= per cent of volume occupied by material= (1 - n)_ volume of solids

total volume_ volume of voids

total volume_ volume of solids

total volume + volume of voids total volume

EmixSince Eair

Emix.

_ T-, (1 - n)“ Esolids

p(l - n) Esolids

4 il

Test results for the dielectric constant determina­tions from the above expressions are shown by Figures 5*1 and5.2 on pages 30 and 31. The results are presented for the natural soil samples as dielectric constant of the pellet and dielectric constant of the soil solids versus plasticity index Test results are tabulated in Table I of Appendix B.

DIELECTRIC CONSTANT of

SOIL

Figure 5.1 DIELECTRIC CONSTANT of PELLET

versus PLASTICITY INDEX30

7.9

7-5

7.0

6.0

00

00

NP 2010PLASTICITY INDEX

19

18

17

16

15(

14

13

12

11

10

9

8,

7

31Figure 5.2

DIELECTRIC CONSTANT of SOLIDS versus PLASTICITY INDEX

(NATURAL SOIL)

5 10 15 20 PLASTICITY INDEX

25

5.6 Second: Series Tests r- Magnetite Removed, .The previous techniques and procedures were used'

again on another complete evaluation of the dielectric con- . i stant 'for the. soil samples iBTter magnetite; removal. The • ;secchd_ program illustrated the influence of magnetite on the dielectric constaht determinations. Results, for both pellet dielectric constant and soil solids dielectric con­stant versus plasticity index, are shown hy Figures 5^3 and•.5.4 on pages 34and 35° Test results are tabulated in ■ ■ Table I of Appendix B., ; :.v :'7; - ^

5.7 cehsistenoy Limits Tests and Grain Size Analyses■ Consistency, limit's tests were conducted, on samples

in accordance with _ American Association of State Highway :#ficlala atandard:'#mod8' of Teati T89-49y T90-49,i and . f T91-49; "Determining the Liquid Limit, Plastic Limit, and Plasticity ".'Index of Soils,. " Analyses of particle Size for 1 all the soil; samples permitted an examination of size influ­ence on dielectric, tesf results; Grain size distribution

' determinations were performed in accordance with American Association of State Highway Officials Standard Method of .Test, T88-49, "Mechanical Analysis 'of Soils.." The soil samples consisted of only minus N o 40 size particles, there- fore, it was not 'necessary to conduct the coarse sieve analy-

; :sls paTt of the. mechanical analysis, test. The fine, sieve and hydrometer determinations were adequate to define particle

■ : ; ■ . 33 size distribution. The particle size distribution curvesfor all fifty soil samples are given in Appendix A.

Figure 5 .3 34DIELECTRIC CONSTANT of PELLET

versus PLASTICITY INDEX (MAGNETITE REMOVED)

U.6

4.5 ►

4.4

4.3

3-4.2

4.1

< )0

(1 0

c0 0

00 <0

) 0% 0n

00

H O - - - O

0 0

0

0 0 0

00 °0

0

0

O

00

0 0

ESo 4.0CO<HO| 3.9 1 3.8

i 3,7

Q 3.6

3.5

3.4

30

3.2

3. I&-5 NP 10 15 20PLASTICITY INDEX

25 30

Figure 5*4

10

10

10.0

9 9 9 9 9 8 8 8 8 8 7 7 7 7 7 6

6 6

6

DIELECTRIC CONSTANT of SOLIDS versus PLASTICITY INDEX

(MAGNETITE REMOVED)

35

oo

o

n c

> X

I»° o

) o >

1o <

oK

oo

o

° > o ti

os o/ o

o

o o o

o

A...........5-81NP 10 15 20

PLASTICITY INDEX25 30

' ',. ' DISCUSSION OP RESULTS

■ 6.1 Accuracy of Plasticity/Index EvaluationsThe results of the plasticity Index de t e rain atIons

Indicate a .range of plasticity from non-plastic soil samples, to samples having a relatively high plasticity index of 29. This range in plasticity encoinpasses, the majority of the f natural soil samples normally encountered in practice„

. , The plasticity .determinations were made by standard procedures and coii^lefed/ in duplicate, by the Arizona 'High-; way’ Departiiient'’ and Wereherfbrmed also in duplicate at the University of Arizona for comparison with the Highway Depart­ment results. The final comparison indicated a maximum: dif~. ference of 3, in.plasticity index while the majority of the results;:Were:- n,early /identlOal. -;;; u" i ” ' : " - ; : '

6.2 Accuracy of Dielectric Measuring Equipment- The accuracy of . the General Radio capacltanoe. .bridge

and sample holder, as claimed by the manufacturer, is +0.1 uuf in measuring differences in capacitance.This represents a maximum inaccuracy of two per cent under most circumstances: Due to the measuring: of .capacitance beyond the limits of the • Standard bridgp-balancing capacitor, an external variable. capacitor was introduced into the circuit. The tolerance of

' . ■■ , • • 37this capacitor was well within that of the over-all unit.

To check the reproducibility of the measurements made throughout the testing program* the general practice of making determinations on the standard acrylic resin pellet before* during* and after the determinations con- - ducted on the soil samples during each day of testing was used. The reproducibility each day was very good and showed a maximum spread for the standard pellet of 2.61 to 2.63.The over-all variation on the dielectric constant of the standard pellet throughout the entire program was from 2.60 to 2,64 indicating a very good reproducibility.

6.3 Soil Pellet ReproducibilityIt was possible to reproduce pellets of identical

diameter due to the fixed dimensions of the forming die.The same amount of soil was used for each pellet but the volume occupied by the material varied* thus causing a vari­ation in thickness from approximately 159 mils to 185 mils.

With accurate determinations of the dimensions of the soil pellets* it was possible to obtain reproducibility of the dielectric constant for each of the three pellets per sample to +1.5 per cent. The dielectric constant result for each soil sample reported in Table I* Appendix B* is the average of the three pellet determinations for each sample.,

6 4 Dielectric Constant of Natural SoliThe ^ detezminations .wer aocom-

plished using the-- capacitance r-eadings ' a M the f ormulas given in the previous chapter, article 5„5„ In general, the results are somewhat higher than generally Accepted when compared with those of Howell and Lieastro (15) for any of - the maJor:Individual constituehts composing the samples,;: The results, for , both the , dielectric constant of the ;

pellet (Sp)::and■ of the solids (Ks) are given in Figures 5 „ 1 and 5*2 on pages 30 and 31/ These figures show the correla-, tion of the 'dielectric determinations.with plasticity index for all of the soil, samples tested/ As evidenced by both of the cerrelatien coefficiehts> 0.29 and 0.28;.the correla- .tion is not strong and no particular benefit is apparent for reducing dielectric constant to that of the - soil solids alone

6„5 Dielectric Constant of Soil With Magnetite RemovedThe dielectric determlnatlotis were accomplished in

a similar manner to that expressed in the preceding- article These values arey in every case/.lower in.magnitude than those for natural,soil and.in much better agreement .with ; those given by Howell and Llcastro in their recent publica­tion. \ ' /yd ' , ' : ' - '

The results for both the dielectrio constant of the pellets (Kg)' and Of the solids (Ks). are given in Figures 5 .3 and 5.4 on pages 34 and 35. The figures, indicate the

correlation of dielectric determinations with plasticity index for the soil P.amples tested. As evidenced by the cor­relation coefficients0>48 and: O.63, of these figures, it . is obvious that the .correlation is much stronger than'indi- ' cated by the-correlation coefficients, 0.29 and 0.28, for the natural soil samples. ' ' . ■ ' f Vr-1- 'v.'':"'''';

6.6 Influence of Grain Size • 'i/r / : . V;: J. ’ - , : rr .The dielectric constants for natural and magnetite-

removed samples and.,their respective • plasticity indices previ - ously described inarticles 6.4 and 6.5 were grouped accord­ing to percentages of minus, 5 micron material. The samples having 13/ +1 per cent of 5 micron material were first grouped toother and correlated.^ the samples haying 1.;13 +2 per cent, 13 +3 per cent, and 13 +4 per cent of 5 micronmaterial .were then-leach grouped and correlated. ' • The results for the magnetite-remoyed samples .are: indicated by Figures• 6,1, 6.2, 6.3 and 6.4 on page 41. ■The correlation coeffi- ;cients, 0 .929, 0.905, 0.551, and p,53y, respectively, .indi­cate -the influence of per cent:clay on the cofreiatipn of : plasticity index and dielectric constants. -

:, I,• - 'The - correlation coefficients of Figures 6.1, -6.2,1; ;-"-•6.3 and 6.4 on page 41. disclose that a high correlationexists:when the per cent 5 mltpbh clay is nearly•equalIfdr .the samples and tends to break down as the spread in percent 5 micron clay.becomeS largcfh• ; wbile this may be true, ’

v;..; • v ' 4 o

it is not the complete picture. These correlations have another- variable which must be considered: number of samples.Table II of Appendix B indicates the number of samples used in each of these correlations and points out that the greater number of samples used, the poorer is the correlation.

6.7 Method of Curve FittingThe method of least squares was used to fit the best

straightvllnes to the data. -This was accomplished using an IBM 650 Computer and an appropriate program. The program Was designed by Dr. Tucker of the University of Arizona and efficiently accomplished the work.

10.0Figure (.1 Ke vs P]9.5 (Magnetite Renoved)

-5/i = 13 ±w 8.5

8.0

° 7.5H

7.0

25NP 205 1510PLASTICITY INDEX

10.0Fig ire 6 . }Kg ys PI

Rmoved)= 13 ±9.0

8.5

7.0

NP 205 1510PLASTICITY INDEX

41

10.0

0)tr;9.5

S 9.0d 8% 3.5H3 8.0oo

B

a

7.5

7.0

6.5

---

FiJKs

jure 6i vs PI

2

(M;igneti',e Reaitived) iNOTE: -5/i =: 13 ± 2$ ^ N <

> / °r Z o-//4

>.(^ z /°

9 /V/

/ O

Gze

NP 5 10 15 20 25PLASTICITY INDEX

10.0cot>d

1dS•s

Iotio

9.5

9.0

8.5

8.0

7.5

7.0

6.5

NP

o---

. F.igiKg i

ire 6J rs PI

k

(Mae 1 NOTE: 5 -5

! Remo> = 13 j

ed)

; ^

Z,

oo yy

o

o(o; o

oS',''

• o

o5 10 15 20 25PLASTICITY INDEX

. Chapter ?.:■

CONCLUSIONS

7.1 Dielectric Measurement Procedure Developed •- ■ S' "'S In searching the literature prior to this investiga­tion, no reference was found;to indicate that the dielectric constant; of soil fihes ' had been or ; could be determined. Prom1, .the;results of this research it can be stated that an effec­tive method has been devised to evaluate the dielectric con­stant for boil fihes and that the magnitude of the value is S in general agreement with the accepted values fpr. the major ' constituent m i n e r a l s composing the soil.;

7.2 Hygroscopic Moisture Control -■ • . Dielectric :constant measurements for'moisture deter­

minations have* been. discussed extensively In the literature.;; Being aware of the influence of moisture in dielectric meas­urements, moderate moisture control techniques were instituted in initial procedures. Less than absolute moisture control .was found to be entirely Inadequate since even the acrylic resin pellet adsorbed moisture when exposed to the atmosphere for long .periods.Of time. In working with extremely hygro­scopic materials, such as bentonites, it is obvious that, to obtain consistently reproducible results, ..extreme care:must ; . be exercised.in moisture control. Any work in dielectric

\ ... . - 43measurement of soil fines must take into account even the smallest amounts of hygroscopic moisture or must eliminate moisture adsorption entirely, A satisfactory technique for moisture adsorption control has been devised.

7.3 Effect of MagnetiteFigure 5-I illustrates the magnitude and correlation

of dielectric constant and plasticity index for natural soil samples. Figure 5°3 illustrates the magnitude and correla­tion for the same samples after they were modified by mag­netite removal. It is obvious that magnetite has a definite effect on dielectric constant determination and on the die­lectric constant-plasticity index, correlation. The influence of magnetite on the dielectric constant was one of the unfore- seen developments and apparently strongly masked correlation between plasticity index and dielectric constant. The im­proved correlation coefficients suggest a definite trend after magnetite removal but not a strong correlation and thus indicate that magnetite is. not the only perturbing factor masking the correlation.

7.4 Influence of Particle SizeParticle size is another of the variables probably

affecting the correlation. The number of samples of equal grain size is inadequate to point out a definite or conclu­sive effect of grain size on the correlation of plasticity index with dielectric constant; however, it is observable

from the data that an effect can be attributed to particlesize variation. . '

The correlation coefficient, r, as indicated on Figure 6.1 is very high, showing' a good correlation between plasticity index and dielectric constant. The high correla­tion was found when the samples had a nearly equal percent­age of minus 5 micron size material. The relation is, how­ever, not well defined due to the fact that few samples had nearly equal percentages of minus 5 micron material. Corre­lations for samples having nearly equal percentages of other sizes (minus 25 and minus 10 micron sizes) were also attemptedwith the results of correlation and number of samples in thecorrelations no different than those of the minus 5 micron analysis.

Since there.appeared to be some correlation of plas­ticity index with dielectric constant in samples of equivalent- sized material, but.the number of samples was inadequate to justify a positive conclusion, it was decided to increase the number of samples in the correlation. This was done by in­creasing the range of the percentage passing minus 5 micron material from 13+1$ to 13+ 2$ for samples to be classed as equivalent. The results are Illustrated in Figure 6.2. The correlation coefficient dropped from 0.929 to 0,905 as the number of samples increased from 6 to 11. This procedure was also utilized for equivalent percentage of minus 25 and minus 10 micron material .and again the results were about

45the same as those for the minus 5 micron size analysis»

The procedure of increasing the range of percentage passing for equivalent size category was applied in two more steps as shown hy Figures 6.3 and 6,4. The results illus­trated by Figure 6.4 are sufficient to show that any attempt at correlation beyond this point would be unwarranted.

Figures 6.1 through 6.4 illustrate that the correla­tion of plasticity index with dielectric constant became progressively less reliable as the range of material less than 5 mlcrohs in size was increased. This increase in range is equivalent to correlating plasticity index with dielectric constant for samples of different particle size distribution. The reduction in correlation as the particle size range becomes progressively larger indicates the impor­tance of particle Size as an influencing variable.

7.5 Need for Additional Research . „;Many unpredictable variables are involved in the

natural soil samples and the relationships are unknown. As the magnetite has definitely been shown to be one of the variables masking a strong correlation, it is evident that others have to be. evaluated or eliminated before a definite conclusion as to the degree of correlation between plasticity index and dielectric constant can be drawn.

FUTURE WORK

8.1 General I- \ ; :v , . The results of this investigation indicate that a.relation hetween'plasticity' Index and dielectric constant probably exists. In the process of developing data to Show this trend, it was Observed that numerous influencing vari- :. ables previously un and: not anticipated, were disclosed.• The degree .and magnitude of the influence of these variables is not completely known, nor predictable at this time.

Since a relation appears, to exist, and the tech­niques and procedures .used permit accurate dielectric con- .- stant determihation fbrlsoll fines, the continuation,of the work is desirable. This may be accomplished using the same . basic techniques but uSihg artificial soil samples, in which some of these variables can;be controlled. ■

8.2: Need for Control of Variables;' v Grain-size, magnetite or heavy minerals/ organic,

content, mineralog1cal-composition, and other variables have been, shown to have•an Influence in the natural soil samples ooyered by this research and produced largely undetermined effects dh the final results. The control of these, variables

w & not anticipated initially, it became obvious only after the research was well on the way to completion,

8,3' Avenue of Research . . ;: The continuation of the investigation using artifi­

cial soils in which variables are controlled should indicate a much stronger trend in the correlation or definitely dis­prove that # Correlation exlstsii ' To accomplish this y art! 1 ■ fieial soil samples'Containing only a few: variables of known magnitude should bef uced^' A desirable beginning would be initiation of research with soil samples of the same grain- sized pure clay mineral and appropriate proportion of the 'Same grain-sized Ottawa Sand to produce variation in plas­ticity and dielectric properties, ■

APPENDIX A

Grain .Size Distribution Curves

PE

RC

EN

T FIN

ER

BY W

EIG

HT

GRAIN SIZE D I S T R I B U T I O N CURVESSample No. Line Symbol Textural Classification Tested By Date Plotted Bv Dote

•AO material only 12-21-60R.L.S R.L.S242Z 12-21-60 12-21-60R.L.S R.L.S

R.L.S 12-21-60R.L.S12-21-60R.L.S 12-21-60R.L.S

Cobble

001 Qjl(S IEVE NUMBER) 270 200 140

P A R T I C L E D I A M E T E R in MM.

O.OOi0.0001 1003 /8 '60 40 20

PER

CE

NT

FINER

BY

WE

IGH

T

GRAIN SIZE D I S T R I B U T I O N CURVESSample No. Textural ClassificationLine Symbol Tested By Plotted BvDote Date

■Ao material only 12-21-602iQ0 R.L.S 12-21-60R.L.S12-21-60R.L.S 12—21—60 12-21—60

R.L.S12-21-60R.L.S R.L.S

R.L.S.if n

Cobble

- .4 ..

ro

O.OOI 001 011 (S IEVE NUMBER) 270 2 0 0 140

00001 100s/a" 3/4" l" l - l /2 " 2 "60 2040 10 4

P A R T I C L E D I A M E T E R in MM.

PE

RC

EN

T FIN

ER

BY W

EIG

HT

GRAIN SIZE D I S T R I B U T I O N CURVESTested ByTexturql Clossificotion Plotted BvDateLine SymbolSample No.

40 material only R.L.SJ.AR.L.SJ.A

R.L.S R.L.SR» L. S.n * w

Cobble

i.O 100001o.ooio.oooi(S IE V E N U M B E R ) 2 7 0 2 0 0 140 6 0 4 0 2 0 10 4 3 /8 " 3 /4 " l" 1-1 /2"2"

P A R T I C L E D I A M E T E R in MM.

PER

CE

NT

FINER

BY

WE

IGH

T

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V / : APPENDIX B' ; ; ■ > ' ' •, ' ■\i- 'r: ■ ■. - ' ■Summary.of Experimental Data

Influence of Content on Gorrelation of ,Dielectnic Const&it^ ! Plasticity ;Index :

piep.

fr3979899DO31321079L4>6>3>4$013*416171319■241923913080139913249452541213>

Table I

SUMMARY OF EXPERIMENTAL DATA 64

Index _ KP Ks Kp Ks Gravity

6.0 7.68 18.6 4.38 9.42 2.7229.0 4.97 9.66 4.02 8.27 2.6617.5 4.88 9.30 3.77 7.83 2.7014.0 4.84 9.23 3.98 7.79 2.6825.0 6.09 13.2 4.42 9.39 2.708.5 4.64 8.91 3.77 7.50 2.7210.5 4.40 9.03 3.99 8.27 2.73NP 4.00 7.92 3.10 5.92 2.7322.5 4.73 10.33 3.84 7.99 2.5910.5 5.14 8.92 3.81 6.77 2.6219.0 6.03 13.2 4.06 8.13 2.7310.0 4.86 9.74 4.20 8.03 2.698.0 4.92 9.70 4.03 7.94 2.7219.0 5.83 12.2 3.92 8.00 2.60NP 6.70 15.1 4.50 9.12 2.7816.0 7.70 17.3 3.89 8.19 2.6717.0 6.61 13.8 3.98 8.11 2.6914.0 5.66 11.7 4.25 7.81 2.688.0 4.81 9.09 3.93 7.53 2.6914.0 5.09 9.87 4.15 7.96 2.6710.0 7.78 18.7 4.12 8.08 2.678.0 5.02 8.71 4.05 7.30 2.68

26.0 5.30 12.3 4.07 10.26 2.7818.5 6.76 15.5 4.14 10.13 2.8610.0 5.87 11.5 4.26 8.23 2.67NP (Sample was not moldable) 2.7621.0 6.69 14.9 4.60 9.84 2.70NP (Sample was not moldable) 2.683.0 4.58 8.65 3.80 7.20 2.7118.0 4.59 9.09 3.71 7.58 2.7114.0 5.05 10.44 3.88 8.41 2.7315.0 5.06 10.13 4.05 8.18 2.7118.0 4.62 9.02 3.91 7.55 2.68NP (Sample was not moldable) 2.913.0 4.24 8.21 3.42 6.51 2.691.0 3.82 7.90 3.09 6.31 2.5914.0 4.90 10.07 3.72 7.54 2.7312.0 4.75 9.96 3.71 8.04 2.62NP (Sample was not moldable) 2.950.5 3.92 7.24 3.38 6.24 2.75

NP (Samp le was not moldable) 2.792.5 4.26 8.05 3.36 6.29 2.7318.5 4.80 9.82 3.87 8.34 2.693.5 4.39 8.16 3.76 6.79 2.713.5 3.99 8.04 3.30 6.12 2.7112.5 4.74 9.73 3.62 7.04 2.7014.5 4.49 8.99 3.70 7.23 2.698.5 4.52 8.30 3.95 7.64 2.6413.5 4.51 8.80 4.02 7.68 2.691.0 5.12 10.56 3.46 6.74 2.62..

6666

1111

11

111 7

1 7

1 7

1 7

2 5

2 5

2 5

2 5

7

7

7

7

1010

10

101212

12

121 9

1 9

1 9

1 9

INFLUENCE OF -5u CONTENT ON CORRELATION OF DIELECTRIC CONSTANT WITH PLASTICITY INDEX

Correlationof

Equation of Best Straight Line

Correlation Coefficient (r)

K p vs P I (Nat) 7 0 . 0 1 5 2 X + 4 . 7 5 2 1 0 . 3 3 3

Ke vs P I (Nat) 7 0 . 2 0 9 I X + 6 . 6 4 6 5 0 . 9 4 9

K p vs P I (Mag,out) Y 0 . 0 0 7 OX + 3 . 8 4 0 6 0 . 2 8 1

Ks vs P I (Mag.out) Y 0 . 1 8 7 3 X + 5 . 1 7 4 5 0 . 9 2 9

K p vs P I (Nat) Y 0 . 0 3 0 9 X + 4 . 4 0 4 0 0 . 6 1 1

K b vs P I (Nat) Y a 0 . 1 5 5 5 X + 7 . 4 0 4 1 0 . 9 0 0

K p vs P I (Mag.out) Y a 0 . 0 1 6 7 X + 3 . 6 7 3 9 0 . 5 6 3

K s vs P I (Mag.out) Y m 0 . 1 4 0 2 X + 5 . 9 5 6 6 0 . 9 0 5

K p vs P I (Nat) 7 m 0 . 0 0 5 6 X + 4 . 7 7 2 9 0 . 0 6 5

K b vs P I (Nat) Y 0 . 0 2 0 6 X + 9 . 3 7 6 3 0 . 0 7 9

K p vs P I (Mag.out) Y tm 0 . 0 0 6 6 X + 3 . 8 2 8 9 0 . 1 6 2

K bvs P I (Mag.

out) Y 0 . 0 8 0 9 X + 6 . 8 5 3 5 0 . 5 5 1

K p vs P I (Nat) Y 0 . 0 2 0 8 X + 4 . 8 1 0 6 0 . 1 5 5

K b vs P I (Nat) Y a 0 . 1 0 1 0 X + 9 . 0 8 0 9 0 . 2 6 4

Kp vs P I (Mag.out) Y 0 . 0 0 5 6 X + 3 . 8 3 9 2 0 . 1 3 9

K8 vs P I (Mag.out) I 0 . 0 8 2 9 X + 6 . 8 5 1 2 0 . 5 3 7

Kp vs P I (Nat) Y 0 . 0 0 1 7 X + 5 . 3 1 6 8 0 . 0 0 7

K b vs P I (Nat) Y 0 . 0 5 9 5 X + 1 0 . 3 6 4 7 0 . 0 9 1

Kp vs P I (Mag.out) Y m 0 . 0 1 6 4 X + 3 . 6 7 5 0 0 . 3 1 6

K bvs P I (Mag.

out) Y a 0 . 0 1 6 2 X + 7 . 7 4 3 8 0 . 2 6 2

K p vs P I (Nat) Y a 0 . 0 3 2 3 X + 4 . 9 1 9 3 0 . 1 2 3

K s vs P I (Nat) Y 0 . 1 8 1 2 X + 8 . 3 9 6 2 0 . 2 6 6

Kp vs P I (Mag.out) Y 0 . 0 0 8 8 X + 3 . 7 9 4 3 0 . 1 8 2

K b vs P I (Mag.out) Y a 0 . 0 5 7 0 X + 7 . 0 1 4 5 0 . 4 8 8

K P vs P I (Nat) Y a 0 . 0 1 7 6 X + 4 . 7 8 5 7 0 . 1 2 5

K bvs P I (Nat) Y a 0 . 0 6 2 7 X + 9 . 4 8 3 9 0 . 1 5 3

Kp vs P I (Mag.out) Y 0 . 0 0 8 7 X + 3 . 7 9 8 8 0 . 1 7 1

K b vs P I (Mag.out) Y 0 . 0 7 5 8 X + 7 . 0 6 4 1 0 . 4 2 4

K p vs P I (Nat) Y 0 . 0 1 3 8 X + 4 . 7 4 2 8 0 . 1 2 7

K b vs P I (Nat) Y 0 . 0 7 8 6 X + 8 . 9 8 4 9 0 . 2 4 0

K P vs P I (Mag.out) Y 0 . 0 0 6 3 X + 3 . 8 1 7 5 0 . 1 5 8

k 8 vs P I (Mag.out) Y 0 . 0 9 0 0 X + 6 . 8 4 2 3 0 . 5 5 5

SELECTED REFERENCES

T C - - Atterb.#rga A. Dle -plastlzltat der tone. Inter . Mitt . :'T911° r ' C ‘ Y ~ \ ,d :

R. Atterbergj A. Die konsistenz und die bindigheit derboden. Inter. Mitt. Bodenk. 2:149-189^ 1912.;

, 3* Banerjee. S.- S. and. Jdshi, R. Di Dielectric Constant, and Conductivity of Soil at High Radio Frequency.. . ; Phil. Mag. 25:1025-1033,: 1938. . , . . '

4. Bear, F.E. (Editor) Chemistry of the Soil. Relnhold' ' ' ' ^ ' ' ■ 3; -'Dri J

5. Berg, G. A. Notes on the Dielectric Separation ofMineral Grainsi - Journar of Sedimentary Petrology. '* 'V. 6, pp. 23-27; 19357^ • y V t d ..; . . .

6.- Cashen,-G. Hi\ Measurements of the Electrical Capacity and Conductivity'of Soil Blocks. Jour, of Agr. Sc. 22:145-164, 1932. ■ -t

• .'./y / d Debye, 'Hi: Eihige Result ate elner ,Kinetischen Theorie :• . der Isolatdreri: Physikj, Zeltz. 13(3) :97a 1912. . -

8. Digest of Literature on •Dielectrics. Nat!1 Res. Council, Nat11 Acadi of Sc. Vols. 1-20, 1920-1956.

9. Eldlefsen, N. E. A Review of Results ip Dielectric :■ Methods for Measuring Moisture Present in Materials.Agr. Eng. 14:242, 1933. v ' v:

10. A New Capillary Potentiometer. Western Soc . Soil Sc. ^: ■ ' 1934. : :. ■*;; .;;r i i ' I eui':'/::. y : . .. . -- '7 ■■. .. 4 :: y:• 11.■Fletcher, Ji E. A Dielectric Method for Determining

Soil Moisture» Soil Sc, of Am. Proc. 4 ; 84-88, 193912.7; Grim,' Ri E, Clay Miueraldgy/ McGraw-Hill^, 1953.13 . Havens, J. H., Young, J. L.,, and . Drake, ¥. B. ■ Some .■ Chemical Physical and Mineraiogical Features of Soil

■' .■Colloids' '’Elghway Res j Board Proc. 29:567-577, 1949.

66

: ' ' ' .... . . / 6?3.4. : Hveem, F. N. Importance of Clay in Applied Soil

Mechanics. Calif. DivV of Mines, Bui. 169:191-195^■ : 1955. : ■ - - , •; ■ -15. Howell, B. P., Jr., and Llcastro, P. H. Dielectric

Behavior of Rocks and Minerals. The American . Mineralogist. Vol. 46, Nos. 3 and 4 (Parts 1 and 2)

: pp. 269-288, 1961.16. Lattey, H . T ., and Catty, 0. The Determination of the

Dielectric Constant of Imperfect Insulators. Phil„ Mag. 7:985-1004, 1929. :

17. Marshall, 6. B. The Colloid Chemistry of Silicate Minerals. Academic Press, Inc., 1948.

18. Purl, A. N. Soils, Their Physics and Chemistry.ReinhoId Publishing Corp., 1949.

19. Ratcliffe, J. A., and White, P. W. C. ElectricalProperties of Soil at Radio Frequencies. Phil. Mag.10:667-680, 1930.

20. Rosenholtz, J. L., and Smith, Dudley T. The DielectricConstant of Mineral Powders. American Mineralogist.V. 21, pp. 115-120, 1936. .

21. Searle, A. B., and Grimshaw, R. W. The Chemistry andPhysics of Clays. Intersoience Pub., 1959.

22. Sen Gupta, B., and Kastgir, S. R. Direct Determination of Electrical Constants of Soil at Radio Frequency.Phil. Mag. 22:265-273V 1946.

23. Terzaghi, K. Simplified Soil Tests for Subgrades andTheir Physical Significance. Pub. Roads. 7:154-162,1926,

24. Yevstigneyev, V. B. The Use of Dielectric Measurements to Determine the Moisture Content of Powdery Substance. Cereal Chem. 16:336-352, 1939.