·e

THE EVALUATION OF A CONE PENETROMETER AS AN INDEX OF FARM VEHICLE MOBILITY

by

Sung Sam Kim

A the sis submitted to the Facu1ty of Graduate Studies and Research in partial fu1fi1ment of the requirements

for the degree of Master of Science

Department of Agricu1tural Engineering, Macdonald Co11ege of McGi11 University, MOntreal, Quebec.

o Sung Sam Kim 1970

December 1969

M.Sc.

ABSTRACT

Sung Sam Kim Agricu1tura1 Engineering

THE EVALUATION OF A CONE PENETROMETER AS AN INDEX OF FARM VEHICLE MOBILITY

An eva1uation of the use of a cone penetrometer as

an index of farm vehic1e mobi1ity is the purpose of this

study.

Tractor performance which inc1uded no 10ad tractor

tests and maximum drawbar pull tests on soft soi1 was re-

1ated to the penetration resistance of the cone penetrometer.

These tests were specia11y p1anned to determine the point at

which the tractor fai1ed to perform as a terrain vehic1e.

The tests were conducted on Ste. Rosalie clay and Soulanges

fine sandy 10am soi1s for Massey Ferguson 135 tractor.

It was found that a co ne index value at 4 inches

depth cou1d be used to predict tractor immobi1ity with no

drawbar pull and that a cone index of a depth of 2.5 indhes

cou1d provide a reasonab1e prediction of maximum obtainab1e

drawbar pull.

It is conc1uded that a cone index can be used to

determine differences in soi1 trafficabi1ity for the farm

tractor.

ACKNOWLEDGEMENTS

The author acknowledges the financial support of

Canada Department of Agriculture in the form of a Research

Grant for this study.

The author wishes to express his deep gratitude to

Professor R.S. Broughton, Chairman of the Department of

Agricultural Engineering, Macdonald College of McGill

University, for his heIpful suggestions, guidance and en­

couragement throughout the course of this study and in

the preparation of this manuscript as thesis supervisor.

The author is glad to express his appreciation to

Professor R.M. Halyk for his advice and numerous vaIuabIe

suggestions during this study.

Special thanks are also extended to his friends,

Mr. E.R. Lising and Mr~ S.C. Negi, who have given much

heIpful assistance, and to Mrs. Jean Vauthier, who typed

so nicely this thesis.

ii

TABLE OF CONTENTS

Page

ACI<NOWLEDGEMENTS • ii

LIST OF TABLES • v

LIST OF PLATES vi

LIST OF FIGURES vii

Chapter

I.

II.

III.

IV.

INTRODUCTION

REVIEW OF' LITERA TURE

2.1. previous Study of Vehicle Mobility 2.2. Factors Affecting Vehicle Mobility 2.3. Measuring Vehicle Mobility · . . · 2.4. W.E.S. Cone Index · · · · · · · 2.5. Theory of Vehicle Immobility · 2.6. Penetrometer · · · · · · · 2.7. Factors Affecting Cone Penetrometer

Performance . . . · · · · · · . . · EXPERIMENTAL APPARA TUS •

· · · · · · · ·

1

4

4 6 9

12 14 16

17

21

3. 1. Cone Penetrometer • • • • • • • • • •• 21 3.2. Test Tractor • • . • • • • • • • • •• 23 3.3. Test Areas and Soil Properties • • •• 27

EXPERIMENTAL PROCEDURE • 29

V. ANALYSIS AND DISCUSSION OF RESULTS • 35

5.1. Soil Physical Characteristic Tests. 35

5.1.1. Laboratory Soil Compaction test. 35 5.1.2. Water Infiltration Test. • • •• 41 5.1.3. Bulk Density-cone Index Relation-

ship . . . . . . . .. . . . . .. 44

iii

Table of Contents (cont'd)

Chapter

V. 5.2. Trafficability Test ••

5.2.1. No Load Traction Test 5. 2. 2. Maximum Drawbar Pull Test

VI. SUMMARY AND CONCLUSIONS

VII. RECOMMENDATIONS FOR FURTHER RESEARCH •

VIII. REFERENCES • • • • • • • • • • • • • •

APPENDICES

A. Terminology • • • B. Data Tables • C. Computer program

iv

Page

47

47 55

62

67

69

75

76 79 83

• LIST OF TABLES

Table

1. Partic1e size distribution - Soulanges fine s;ëlI1Ci~ JL()ëtD! • • • • • • • • • • • • • • • • • •

2. Partic1e size distribution - Ste. Rosalie clay . . . . . . . . . . . . . . . . .

3. The effect of moisture content on soi1 compac­tion, 1aboratory soi1 test for fine sandy loam

4. The effect of moisture content on soi1 compac­tion, 1aboratory soi1 test for clay soi1 •

5. Bu1k density-cone index re1ationship . •

6. Tractor performance with cone index on the

Page

28

28

clay soi1 • • • • • • • • • • • •• • •• .81

7. Whee1 sirikage-s1ippage re1ationship 82

8. Maximum drawbar pull test - Ste. Rosalie c.1ay. 83- '

9. Maximum drawbar pull test - Soulanges fine sandy loam • • • • • • • • • • • • • • • • : 83

v

LIST OF PLATES

Plate Page

1. Portable, electric speed controlled cone pene-trometer • • • • . 22

2. Test tractor • • • • • • • • • • • • • • • • •• 26

3. Artificial soil-wetting prior to trafficability test . . . . . . . . . . . . . . . . . . . . .. 30

4. Travel reduction measurement • • • • • • • • •• 32

5. Tractor at stuck point . . • • • • • • • • • • • 32

vi

LIST OF FIGURES

Figure Page

1. Layout of components for soil penetrometer circu.it . . . . . . . . . . . . . . . . . .. 24

2. A representative sample of penetrometer read-ings

3. Soil compaction test: penetration resistance vs. penetration depth for different values of

34

soil moisture content • • • • • • • • • • •• 37

4. The effect of soil moisture content on soil compaction 38

5. Water infiltration tester • • • 42

6. The influe~ce of soil water infiltration on the cone penetrometer readings •• • • • 43

7. Variation of cone index with bulk Qensity 46

8. The effect of cone penetration resistance on the tractor mobility on Ste. Rosalie clay soil

9. Limit of tractor mobility •

10. Cone index vs. slippage for several penetro­meter depths, no-drawbar pull, Ste. Rosalie

48

49

clay soil . . . . . . . . . . . . . . . . .. 51

Il. The variation of tractor wheel sinkage with slippage • • • • • • • • • • • • •• 53

12. Cone penetrometer resistance with different maximum drawbar pulls on st~. Rosalie clay 56

13. Cone penetrometer resistance with different maximum drawbar pulls on Soulanges fine sandy loam . . . . . . . . . . . . . . . . . . .. 57

vii

List of Figures (oont'd)

Figure

14. Cone index vs. drawbar pull for co ne indexes obtained at several penetrometer depths, Ste.

Page

RGsalie clay soil • • • •• • • • • • •• 58

15. Cone index vs. drawbar pull for cone indexes obtained atseveral penetrometer depths, Sou-langes fine sandy loam • • • • • • • •• 59

viii

I. INTRODUCTION

Mechanization in agricu1ture in the twentieth century

has'been a major factor contributing to outstanding deve10p­

ments in food production per farm worker and to the advance­

ment of civilization. Under economic and sociologie pressures

field crop mechanization continues to move toward larger mo­

bile power units and associated maChines.

Extensive use of large mobi1e power units and the

need to grow intensive annua1 crops with critical planting

and harvesting timing in humid c1imate regions bring on

problems of farm vehicle mobi1ity and soil compact ion.

If tractors and maChines s1ip excessively, and even

get stuck, in field operations, not only does the field effi­

ciency of the machines decrease but a1so the soil structure

is damaged and crop yields are decreased. Damage to struc­

ture of clay soils may also reduce water infiltration and

cause even poorer traction conditions in the future.

More efficient use of powered field machir"'''· 3 and par­

ticularly tractors will be the focus of further emphasis in

the future. To reduce machine and field operation costs it

is desirable to extend the number of hours and days that

field operations can be undertaken. To aChieve this goal,

2

something suCh as sub-drainage might be done to improve

soil surface travel conditions, or sorne Changes might be

made in the design of the power maChines to improve their

mobility on the soils as found. As a fundamental factor of

the tractor operation, soil will determine the traction

performance to a muCh greater extent than any operational

control or design factor.

Soil condition is described by many parameters, for

example, strength in shear, tension and compression, plastic­

elastic flow, water content, friction, cohesion, particle

size distribution, Chemical constitution, and temperature.

It has not yet beeD possible to correlate aIl of these fac­

tors with vehicle mobility. It would be very desirable to

have a simple compact device which is easy to operate in

the field or the laboratory, to de termine the relation be­

tween soil physical properties and the tractor performance.

This would aid both. in the design of better tractors and in

the specification of field requirements suCh as sub-drainage,

surface drainage, clean cultivation, field size, etc.

Much of the drainage research done in the past has

aimed at improving crop yields and extending the crop season

between planting and harvesting. Drainage research workers

recognize that Changes in mechanization and the difficulties

of hiring people to harvest manually indicate that the main

criterion for drainage improvements in the future will be

improved farm vehicle rnobility rather than crop yield.

3

Crops will be harvested mechanically rather than by

hand. It is yield of high quality food and feed at the con­

surnption point rather than merely yield on the plant in the

field which is important. Drainage research workers have

not yet found a suitable, convehient way of defining ade­

quate soil trafficability.

The soil penetrometer has been used as a means for

evaluating the mechanical strength of the soil and predic­

tion of rnilitary vehicle rnobility by the U.S. Army Corps of

Engineers. There seemed good promise of using a cone pene­

trometer to obtain an index of farm vehicle rnobility to pro­

vide guidance for further improvernents in land drainage de­

sign or farm vehicle design. It is the purpose of this

study to provide an evaluation of the use of a cone pene­

trometer as an index of farm vehicle rnobility, and to ob­

tain sorne experience with vehicle rnobility problerns on St.

Lawrence Lowland soils, and to suggest the emphasis needed

for further work on land irnprovements and farm vehicle

design.

4

• II. REVIEW OF LITERATURE

2.1. previous Study of Vehic1e Mobi1ity

The 1ack of a genera1 re1ationship between the per-

formance of a vehic1e and its physica1 environment has been

recognized for many years. Recently, greater emphasis has

been p1aced on the basic aspects of soi1-vehic1e mechanics

for mi1itary mobi1ity, agricu1tura1 mechanization, and earth

moving equipment. In the past twenty years there has been

an increase in research effort in this field to obtain a

• better understanding of the action of soi1-vehic1e systems.

~e purpose of these investigations has been the prediction

and eva1uation of performance and design:~ for off-the-road

or cross-country locomotion vehic1es. These studies are

genera11y directed toward the prob1ems in the field by land

vehic1es operating over loose or soft soi1. Basic prob1ems

in these soi1 types are excessive whee1 or track sinkage due

to physica1 characteristics of both the soi1 and the vehic1e,

and excessive whee1 or track slippage caused by a combination

of insufficient shearing strength of the soi1 and vehic1e

characteristics. > . • Since Mick1ethwaite (1944) tried to predict the maxi-

mum possible tractive effort of tracked vehic1esby application

5

of the well known Coulomb equation (S = c +.p tan~), Bekker

and his colleagues at the Land Locomotion Laboratory at

Warren, MiCh., U.S.A., contributed to the foundation of pres­

ent theoretical work (Bekker, 1956: Bekker, 1960: Liston,

1965: and Reece, 1965). Also the Ar.my Mobility ResearCh

Center of the U.S. Army Corps of Engineers at the Waterways

Experimental Station, Vicksburg, Miss., U.S.A., has conducted

research to determine the trafficability of soil since 1943.

Knight, Freitag and Rush et al. have adopted an empirical

approach to determine whether a particular soil condition

is trafficable for a particular vehicle (Forster and Knight,

1955). The empirical approaCh consists of a correlation of

cone penetrometer reading with the ability of soil to support

traffic.

Recently Reece (1958, 1965, 1967) and his colleagues

at the University of Newcastle upon Tyne, Great Britain,

conducted some experimental tests of Bekker1s theories and

also made significant theoretical contributions.

McKibben (1960), Vanden Berg (1962), Gill (1968),

Taylor (1968) and many researchers of the National Tillage

Machinery Laboratory of the U.S.D.A. have worked to deter­

mine the basic dynamic relationships of the various forces

acting on wheels or tools and the soil, and soil reaction

using large soil bins in which full size wheels, tracks,

6

vehicles and tillage tools are operated (Gill and Vanden

Berg, 1968). Although they reported many tillage techniques

and the resulting soil compaction, they were prirmarily con­

cerned with dynamic properties of the soil, and soil traf­

ficability was only noted indirectly (MêKibben, 1940:

Nichol, 1923).

Several other university laboratories are undertaking

experimental and theoretical developments in terramechanics.

2.2. Factors Affecting Vehicle Mobility

The mobility and traction performance of a vehicle is

determined by the relationships between all environmental con­

ditions and vehicle factors.

In general, environmental conditions affecting mobility

can be expressed in three families: soil physical properties

(Perrson and Vanden Berg, 1968: Smith, 1966; McKibben, 1940):

surface compositions (Bekker, 1960; W.E.S., 1963, 1964); and

the climate (Rutledge and Machardy, 1968). The vehicle fact­

ors are also divided into vehicle form, weight, and support­

ing devices including dimensions such as wheel or track size,

contact pressure. In farm operations, however, the perform­

ance of a vehicle on the soil may be described by its mobil­

ity and tractive effort produced.

This tractive effort (D) is tractive thrust (H) minus

7

vehic1e ro11ing resistance (R) (Bekker, 1956; Reece, 1965):

D=H-R

For the tractive thrust (H), a modification of cou­

lomb's shear strength equation (S = C + P tan~) has been

deve10ped by Bekker (1956) and many others (Onafeco and

Reece, 1965, 1967; Masuta and Tanaka, 1966). They proceeded

from there to the deve10pment of an equation for thrust in

the manner of Mick1ethwaite (1944) who mu1tip1ied both sides

of the Coulomb equation by the ground contact area and ob­

tained

H = (AC + pA tan~)

AlI of these modifications attempted to account for

the effect of disp1acement on soi1 shear strength.

A1so ro11ing resistance (R) theories were deve10ped

based on pressure-sinkage 1aws - an ide a that originated with

Bernstein (p = kzn) (1913), and which have been deve10ped

principa11y by Bekker (1956) and Uffe1man (1961).. Experi­

mental investigations (Wi11s, 1965; Vincent, 1961; Hegedus,

1965; Onafeco, 1967; Sitker, 1961) showed that ro11ing resist­

ance shou1d be considered as a function of slippage which is

re1ated to the soi1 fai1ure pattern. Assuming the stress­

strain in the ana1ysis of the pressure-shrinkage re1ationship,

the bearing capacity is a1so considered by many researchers

8

(Reece, 1965~ WiendieCk, 1968~ Wong and Reece, 1967) such as

soil shear strength for development of equation to predict

traction performance. The general Terzaghi (Terzaghi and

PeCk, 1948, p. 170) soil bearing capa city equation is:

q = CN + rDN + ~l'BNr c q

where

q = ultimate bearing capacity (psf) B = width of footing (ft)

c = soil cohesion (psf) r= unit weight of soil (lb)

Nc,Nq,Nr = Terzaghi's bearing capacity factors

D = depth from the ground surface to bottom of footing (ft)

Bekker (1956) proposed that soil trafficability cou Id

be defined in terms of values which have a more real physical

meaning: 1. cohesion - C

2. soil friction angle - ~

3. specifie gravit y - r 4. structural soil constant - KI' K2

5. modulus of sinkage - K

6. exponent of sinkage - N

The values of C and ~ are determined by constructing the

shear strength envelope from in situ shear device data. KI

and K2 coefficients are determined by using shear stress-

strain curves for a given soil. The value of N expresses

the physico-geometrical structure of the soil profile, and

9

the K relates the soil properties as weIl as the form and

size of the loading area. But these Bekker soil parameters

have limitations such as those pointed out by Reece (1965)

and Clark (1967), for applying to general soil-vehicle prob­

lems, and they also have many difficulties for practical

purposes.

Thus, soil trafficability is defined in terms of soil

shear strength, bearing capacity criteria and such factors as

cohesion, friction and bulk density. Vehicle mobility is

also affected by the interaction of the soil trafficability

and vehicle characteristics.

2.3. Measuring Vehicle Mobility

Engineering evaluation of terrain vehicle systems is

based on measurements of a number of parameters of the math­

ematical models of soil-vehicle relationships. The main

requirement for developing these methods is to make the

loading conditions of the vehicle and the loading conditions

exerted by the soil-measuring apparatus as similar as pos­

sible. Accordingly, since Bernstein (1913) had introduced

soil penetration tests, the Waterways Experimental Station

(W.E.S.) of the U.S. Army Corps of Engineers developed a

non-recording penetrometer to define soil trafficability

(W.E.S., 1947). Also in the same period, a British Military

Operations Research Unit deve10ped a penetrometer with a

circu1ar plate, and a recorder to plot the constant rate

load-penetrations curve for the measured soil strength

(Evans, 1948).

Measurement of soil friction and cohesion was pro­

posed during the wartime studies of mobility in England

10

(MiCk1ethwaite, 1944). The first field instrument for that

purpose was developed independently in Canada,practically

at the same time (Bekker, 1947). This state of the art in

terrain measurement prevailed until 1955, when the need for

more quantitative information became urgent and new types

of measurements were introduced. These were based on the

concept of vertical and horizontal stress-strain relation­

ships, and on the definition of geometry of terrain rough­

ness (Bekker, 1969).

Empirical studies of soil trafficability were carried

out by the U.S. Army Corps of Engineers (W.E.S., 1948).

Measurement of mud viscosity in studies of mobility was un­

known until a decade ago (Bekker, 1969).

Recently, a bevameter has been developed by the U.S.

Army Tank Automotive Cornmand's Land Locomotion Laboratory

(Bekker, 1956; Reece, 1964; Liston, 1965). This instrument

consists of two or three penetration plates, and shear plates

together with appropriate recorders of stress-strain

•

•

•

:

Il

relationships. Several types of the bevameterhave been

developed by the vehicle mobility research laboratories (Reece,

1964; Bekker, 1960: Bekker, 1969).

The bevameter teChnique, which applies to aIl soils

and· snow and consists of a number of penetration tests and a

shear test, produces a number of soil parameters. In addi­

tion, the correlation of bevameter data with vehicle design

and/or performance parameters can he achieved throughexperi­

mentally tested mathematical models. Furthermore, the sev­

eral indices defined by a number of shear and penetration

tests conta in more information (Bekker, 1969). Although

this bevameter is particularly useful in cases such as lab­

oratory investigations under fully controlled conditions to

verify mathematical models of soil-vehicle relationships,

this structure is also too complex for practical purposes,

and a simpler more versatile one is required for use on a

farm.

Another method for determining soil characteristics

developted in the early 1940's by the Wate:rways Experimental

Station, has lumped the mechanical properties that char­

acterize soil bearing strength and thrust resistance into

one value, called the cone index.

12

2.4. W.E.S. Cone Index

The cone index is defined as the force required to

sink the cone divided by the cone base area. A rating cone

index is used to estimate the cone index that will be ob-

tained under a moving vehicle operating on fine grained

soils (Knight and Freitag, 1962).

The rating cone index is ·obtained by multiplying the

in situ cone index by a remolding index whidh is obtained by

measuring the cone index of the soil confined in a small

cylinder before and after pounding it with 100 blows of a

2~ pound tamper fa11ing 12 inches. Tb determine whiCh

cone index is to be used, soils are classified as fine-

grained or sandy.

Knight and Freitag (1962) reported that the rating

cone index taken from a given area can be used to predict

confidently -

1. whether a given vehic1e can cross the area once

2. whether 50 vehic1es can cross the area in the same traCk

3. the load that a vehicle can tow through the area, or

4. the slope that the vehic1e can negotiate in the area.

The mobility index system out1ined by Knight and Freitag

(1962) was developed to assist in evaluating the effects of

vehicles characteristics on the mobility index formula.

e developed for self-propelled wheeled vehicles operating on

fine-grained soils. This was given as:

where MI = Mobility Index

Pf = gross weight in lbs tire width xrim diameter x number of tires

Wf = weight factor

greater than 3,500 pounds = 1.1

1,500 to 3,500 pounds = 1.0

less than 1,500 pounds = 0.9

tf = tire factor = 1.25 x tire width in inChes/lOO

tIf = tire lug factor = 1.05 with chains

1.00 without chains

W = wheel load = gross weight number of wheels

Cf = clearance factor = clea~~nce (inCh)

Ef = engine factor = 1.0 greater than 10 hp per ton

1.05 less than 10 hp per ton

Uf = transmission factor = 1.0 hydrau1ic

1. 05 meChanical

13

Vehicle cone index can be predicted from the relation

between mobility index and vehicle cone index.

But in spite of the considerable efforts that have been

made in the direction of solving this mobility problem, the

14

cone index is used only as a means of indicatingthe soil

strength. Bekker (1956)pointed out that "these soil stren-

gth factors did not provide the sought for definition of

trafficability because the theoretical knowledge of the re-

lationship between shearing strength of soil and vehicle

locomotion was not considered." As yeti there are· not enough

theoretical analysis relatingvehicle motion and the cone

penetrometer readings. Also these various cone indices apply

only to particular military vehicles which have different

requirements from farm vehicles.

For milita:cy vehicles:

1. General traffic unit is passage of 50 vehicles.

2. Soil characteristics of the area are not known.

3. Power efficiency is of little concerne

4. Damage to soil structure for future crop growth is disregarded.

For agricultural vehicles the above points should be

taken into consideration.

2.5. Theory of Vehicle Immobility

Vehicle immobility can be divided into two extreme

cases:

1. when a wheel device sinks deeply into sticky mud

and is just capable of moving itself forward so that its net

15

pull is zero, the whee1 wi11 probab1y be spinning,

2. and the other case when the ro11ing resistance is

the same as or bigger than the soil thrust or input energy,

the wheel wi11 be braking.

According to the suggestion of Bekker's tractive effort

equation, these phenomena can be indicated

from D = H - R

1. H = 0 (spinning)

2. R ~ H (braking)

At present, the spinning state (forward velocity =

0) seerns to be the most 1ègical basis on whidh to define the

stuck point and thus provide one of the more important

criteria of performance. It occurs usually in extremely

soft soil or stiCky and s1ippery soi1.

Particular1y in the case of conventional rear-wheel

drive tractors, the tractive effort is a function of the

front and rear whee1s ro11ing resistance and front axle

load towing force.

where

D = H - (Rf + Rr) - Wf

D - tractive effort

H - soil wheel thrust (per unit contact area)

Rf- front whee1 ro1ling resistance

Rr- rear wheel r011ing resistance

Wf-front ax1e 10ad towing force

As a tractor, its tractive effort is zero at the spinning

point since aIl input energy is lost in the contact zone.

This spinning state can be a1so c1early defined as energy

loss (Yong, 1966: SChuring, 1966).

2.6. Penetrometer

16

Since measuring soil strength is a difficult and in­

convenient process, soil scientists have searched for sim­

pler and more convenient methods of measurement. Because

of their relative simplicity of construction and use, and

because of their ability to be used in the field as weIl as

in the laboratory, penetrometers have been used to obtain

soil strength indications.

Many sizes and shapes of penetrometers have been

employed including: Needle penetrometer (Bernstein, 1913)~

Impact penetrometer (Nichols, 1923): Co ne penetrometer

(Proctor, 1933~ Richards, 1941): Drop-type penetrometer

(stone and William, 1939).

Penetrometers can also be divided into two groups

depending on the methods of applying force:

1. static penetrometers, and

2. impact penetrometers.

The majority of penetrorneters have been the static

17 ,

type, because the static penetrometer is a simp1er instru-

ment than the impact penetrometer. Two mathematica1 mode1s

are used depending on the teChnique of driving the penetro-

meter into the soi1. At Vanden Berg and Gillis suggestion

(1968), (1) one mode1 expresses the force required to cause

penetration, either in terms of magnitude or on a unit area

basis (genera1 penetrometer): (2) the other mode1 measures

the energy required to cause penetration (Ze1enin, 1950:

House1, 1939). Genera11y an average energy value over some

depth is considered representative of penetration resist-

ance.

Some recording penetrometers have been deve10ped

to provide a continuous record of resistance with depth for

various special purposes (Vanden Berg and Gill, 1967: Broms,

1965: Mathieu, 1958: Proctor, 1968: Terry, 1968: Wi11iford,

1968).

2.7. Factors Affecting Cone Penetrometer Performance

Since the W.E.S. has deve10ped the cone index system

for deterrnining soi1 trafficabi1ity by cone penetrometer,

some researchers have concentrated on the investigation of

the re1ationship of the cone characteristics and soi1 condi-

tions. These resu1ts are as fo11ows:

18

1. The cene tip size and angle effects.

The W.E.S. (1948) reported that the shape of the

tip of the probe hadlittle effect on the resistance to

penetrometer projected end area. But recently many resear­

chers who studied the influence of the geometry of penetro­

meters on resistance to penetration with dimènsional anal­

ysis techniques, reported that (a) for any given tip shape

penetr0meter tip size and an.gle had no effect on the trans­

formed data (i.e. bath model and prototype tips conformed

to the theoretical relationship (Kondnor, 1962): (b) the

only apparent effect of variation of tip size was in the

magnitude of the penetrometer load-depth readings. The

functional relationship was unchanged (Shuman, 1967).

2. The size of the cone shaft.

The size of the penetrometer shaft relative to the

diameter of the cone can influence the results of the test

(Freitag, 1967). If the shaft is relatively small, the

pressure relief will tend to reduce the penetration re­

sistance. On the other hand, if the shaft has nearly the

same diameter as the cone, the drag of the soil on the

shaft could cause an apparent increase in penetration re­

sistance.

3. The sFeed of the penetration into the soil.

The speed of the penetration into the soil also

19

affects the pressure required to cause the penetration. The

penetration resistance is relatively low at slow speeds but

increases as the speed of the penetration increases in a

wet, fine-grained soil. In sandy soils little or no speed

effects were observed other than those that cou Id be accounted

for by inertia effects (Freitag, 1967).

4. The relation of soil shear strenqth and penetrometer.

Smith (1966), Shuman (1967), Freitag (1967), Gill

(1967) and Williford and Larson (1968a) also studied indi­

vidual factors such as soil bulk volume weight, cohesion,

frictional angle and shear strength relate with cone index

for many soils.

5. The very thin soil surface condition.

From the results of a study of the effect of wet

surface soil conditions on the performance of a single

wheel (Smith, 1966), a cone penetrometer does not completely

describe the effects of the soil variable on pull when water

is introduced. This is not unreasonable, because the cone

index is a gross description of a group of soil properties,

while the loss of pull in the flooded test is due to a thin

film of weak material on the soil surface. If the cone

index used is from the soil resistance at a six-inch depth,

the surface condition is not adequately measured.

Willford (1968) reported that the cone index is an

indication of the soil condition at the depth of the cone

tip rather than at the base of the cone.

General conclusions are that cone penetrorneter is a

useful field instrument and a test device for sorne of the

more simple soil conditions.

20

21

III. EXPERIMENTAL APPARATUS

3.1. Cone Penetrometer

In preliminary tests using a W.E.S. portable cone

penetrometer it was not possible to obtain consistent re­

sisting force measurements because it was not possible to

have a constant penetration speed when forcing the penetro­

meter into the ground by hand.

The penetrometer used in this study was designed

for use both in the field and in the laboratory. It was

mounted on the frame as shown in Plate 1. The cone and

stem are forced into the soil by a motor. The speed of

penetration is varied by changing the motor speed by use of

an electrical control system. The force on the penetro­

meter cone was measured by a strain gage which produced an

electrical signal proportional to the resisting force of

the soil. The potentiometer produced an electrical signal

proportional to the extension of the position of the pene­

trometer point. These electrical signaIs were transmitted

to an X-y recorder which plotted the axial force acting on

the cane as a function of the depth of penetration into

the sail.

The zero point was arbitrarily selected as the

PLATE 1. PORTABLE, ELECTRIC SPEED CONTROLLED

CONE PENETROMETER

22

(

(

PLATE L PORTABLE, ELECTRIC SPEED CONTROLLED

CONE PENETROMETER

22

23

point at which the tip of the cone was level with the sur-

face of the soil. This means that, due to the irregulari-

ties in the soil surface caused by cultivation or tillage,

the zero reading is not always the same.

A circuit diagram of the force measuring system is

shown in Figure 1.

The cone used on the penetrometer had an included

angle of 30 (degrees) with a cross sectional base area of

~ square inch and was made of stainless steel. The stem

diameter was 0.625 inches.

3.2. Test Tractor

The Massey-Ferguson model 135 (gasoline engine)

farm tractor used for the field tests had the following

pertinent data:

Weight

Tires

Gross 3,566 lbs. (including driver. but no wheel balast)

Front axle 1,326 lbs.

Rear axle 2,240 lbs.

Nominal width (inch) Front-6 Rear-12.4

Rim diameter (inch) Front-16 Rear-28

Nominal outside (inch) Front-28 Rear-50.4 diameter

Inflation pressure (psi) Front-20 Rear-15

Ply rating Front-4 Rear-4

+ +

y INPUT

X INPUT

y AXIS CALIBRATION

SWITCH

1 2

12500

330 K

X AXIS CALIBRATION

FIGURE 1. LAYOUT OF COMPONENïS FOR SOIL

PENETROMETER CIRC UIT

24

y - AXIS CALIBRATION CIRCUIT

r _S~_n_s_ijj.y! 'tt J~P-l1.~. 1 1 1 1

~---~---T-------------------------------~ 1 1 : 5K pot 270 : ~----------------~

-=.6V Rz1

y - IN PUT

3

R1 = R2 = R3 = R4 = 120 1,000 Then

Rz 2 = 100R1 = 12,000 RZ2 used = 12,500

6V

Rz1 = 25 K pot

Sensitivity Control

strain gage

lower 1imit

current 1imit 6 = _ll' __ = ____ _

Rt 5,270 V 6 -----= upper 1 imi t = ----=

270 R

l = 0.03 amps.

= 1.14 ma.

22.2 ma.

x - AXIS CALIBRATION CIRCUIT

J turn • Zero Adjust lOOK pot X - IN PUT

Zero Adjust

- Determines maximum range of x def1ection.

- Compensates for battery ageing·'.

25

26

PLATE 2. TEST TRACTOR

ft

26

PLATE 2. TEST TRACTOR

('

Maximum drawbar pull 2,147 lbs. (5.28 mph)

at slip 7.82%

(on the Nebraska Test - No. 899)

3.3. Test Areas and Soil Properties

TWo test areas, located near st. Clet in Soulanges

County, Quebec, about twenty miles ~outhwest of Macdonald

College, were used in this study. The soils in the test

areas were classified as a heavy clay, Ste. Rosalie clay

(Mr. Martineau farm), and Soulanges fine sandy loam soil

(Mr. Vincent farm).

27

The fine sandy loam and clay soils are potentially

fertile but suffer from poor or imperfect drainage because

of the fIat topography of the region and low permeability

of the subsoil which makes farm vehicle mobility a severe

problem, particularly in the early spring seedbed prepara­

tion time and at harvesting time. These two soils are re­

presentative of large acreage of st. Lawrence lowland soils.

The particle size distributions of the soils at the test

sites as found by Tu (1968) are given in Tables 1 and 2.

A more complete description of the soils at the test site

is given by Tu (1968). Vehicle mobility tests were made

for ploughed and unplowed conditions in the 1969 spring on

both soils.

28

Table 1. Particle size distribution

Vincent's field (Soulanges fine sandy loam)

Depth Clay Silt Sand (in) (%) (%) (%)

o - 6 13.0 12.0 75.0

9 - 15 3.5 9.5 87.0

18 - 24 11.5 9.0 79.5

30 - 36 62.0 30.0 8.0

Table 2. Particle size distribution

Martineau's field (Ste. Rosalie clay)

Depth Clay Silt Sand (in) (%) (%) (%)

o - 6 40.5 30.5 29.0

9 - 15 50.5 29.5 20.0

18 - 24 46.0 33.0 21. 0

30 - 36 48.0 31.5 20.5

29

IV. EXPERIMENTAL PROCEDURE

Tests were conducted by running the tractor in its

low-third gear at a speed of approximately 4 m.p.h. These

tests included no load tractor tests and maximum drawbar

pull tests with a four-wheel drive truck towed against com­

pression by the tractor. Tests were conducted on soft soil

and on artificially wetted soil as shown in Plate 3.

For the drawbar pull tests, the tractor was made to

move forward in a straight line path at a constant engine

speed. The four-wheel drive truck vehicle was put in gear,

with the brakes off and provided a near constant pull when

towed by the tractor. A hydraulic dynamometer, at the end

of the cable at the rear of the tractor, measured drawbar

pull. Tests were carried out with the truck set in differ­

ent gears to provide different drawbar pulls.

In each test, as soon as the tractor moved forward,

a stick was placed in the ground to mark the beginning of

one revolution of the rear wheel on whose side a line was

drawn to help the observer to note the complete revolutions.

With the tractor continuously moving, sticks were placed in

the ground to indicate the distance travelled by the tractor

after each revolution of the rear wheels as shown in Plate 4.

PLATE 3. ARTIFICIAL SOIL- WETTING PRIOR TO

TRAFFICABILITY TEST (SEPTEMBER, 1968 )

30

(

PLATE 3. ARTIFICIAL SOIL- WETTING PRIOR TO

(-TRAFFICABILITY TEST (SEPTEMBER, 1968 )

\

31

Wheel slippage was then deter.mined by measuring the distance

between the sticks. Also sudh factors as soil compact ion

and sinkage were measured in eadh track directly after each

test. Cone-penetrometer readings, soil moisture content and

buIk volume weight, were measured outside the zone of disturb-

ance created by the wheel of the tractor near the position

where the tractor failed to move forward and at intervals

along the route in the region of significant slippage approa-

Ching the point of getting stuck.

,"/

Tractor performance was related to the force dis-

placement characteristics of the cone penetrometer. These , ~l

tests were specially planned to de termine the point at

whiCh the tractor failed to perform as a terrain vehicle (go

or no go) (shown in Plate 5). Soil samples were taken to

find the moisture content and bulk density at two inch\'.

vertical increments to a depth of 12 indhes. Since the effect

of speed of penetration was not considered in the study, a

constant speed of 72 inches per minute was used throughout

the tests as recommended by Freitag (1967).

A series of six penetrometer readings were taken at

random in the region of high slippage in the test area at

positions either between or just outside the wheel tracks.

The six readings were then combined to obtain an average

32

PLATE 4. TRAVEL REDUCTION MEASUREMENT

PLATE 5. TRACTOR AT STUCK POINT

(:.~ ... \ \;.~~~·ï

PLATE 4. TRAVEL REDUCTION MEASUREMENT

.' .-- . ;'*·.· .... 0-'·_·;·,~

PLATE 5. TRACTOR AT STUCK POINT

32

33

force versus depth curve for the test. By dividing the

force by the cross-sectional area of the base of the cone, a

cone index was obtained. Then, a plot of cone index versus

depth was drawn (a representative sample is shown in Figure

2). The cone index showed a definite variation over the

depth range studied. There was not much variation in the

force required to penetra te the soil near the surface at

the several locations along the test strip. For depths

greater than seven inches the required force varied greatly.

This may be due fiEstly to the cultivation of the top soil

giving more uniformity in the top seven inches than lower

down, and secondly, to the surface of the soil in the test

fields not being fIat. ~ughness undulations of up to

two inches were quite possible on the plowed or cultivated

soil. Thus the penetrometer might strike the harder soil

below the plough layer at six inches in one place or at

eight inches in another place. A depth difference of two

inches could cause sorne of the variability between the

graphs for two different rneasuring locations.

e e e

300 > i •.

:A copy of penetration curves obtained in the

250 Soulanges fine sandy loam field

- t NO LOAD DRAWBAR PULL TEST N

~ 200 t wheel sinkage • 3.5 inch. , slippa ge • 24 (°/0) ,

..J

- SOll WATER CONTENT

i 150

1

,

depth 0 11- 3 11 43 (%)

3 - 6 35

6 - 9 30 ~ 100 t 0 9 - 12 24 0

50

MAY 14 t 1969

o o 2 3 4 5 6 7 8 9 10 Il I~ 13 ~

penetration depth (Inch)

FI G. 2. A REPRESENTAT IVE SAMPLE OF PENETROMETER READINGS IN THE FIELD

35

v. ANALYSIS AND DISCUSSION OF RESULTS

Results and discussion are given for the tests to

determine (l) the relationship between soil physical Char­

acteristics and penetrometer readings, (2) the vehicle mobil­

ity of a farm tractor and penetrometer readings and (3) max­

imum drawbar pull for certain soil conditions.

The value of the co ne index (p.s.i.) and penetro­

meter tip depth were taken from the X-y Recorder Chart. The

program for the I.B.M. 360 computer shown in the APpendix

was used to convert these data to the analysis equations

presented.

5.1. Soil Physical Characteristic Tests

5.1.1. Laboratory Soil Compaction Test

Experiments were undertaken to determine whether

there appeared to be any consistent relationship between soil

compaction and the soil penetrometer readings and between

soil moisture content and the penetrometer readings.

It is probable that different results would be ob­

tained with a different compaction procedure. However, since

the main object of the research for this thesis was to obtain

observations on vehicle performance, the laboratory compaction

tests were made only to check out the reliability and repro­

duceability of the penetrometer readings in a particular soil.

36

The method of preparing the soil for these tests was similar

to the processing of the soil which is used in laboratory

soil bins and is subjected to surface compaction.

The ste. Rosalie clay and Soulanges fine sandy loam

soils were prepared in accordance with the procedure as de­

scribed for Method A in Section 3,4 (A.S.T.M., 1964, Designa­

tion D-1557-67T, p. l20) except that the compaction device

consisted of a steel cylinder six inches in diameter and 18

inChes long and a drop hammer weighing 10 pounds. For the

tests, the cylinder was filled with thesoil and the drop

hammer was made to drop ten times on the soil from a height

of 18 inches.

Triplicate penetrometer resistance tests were made

for each soil moisture content. The results of cone index

versus depth·measurements are given in Figure 3. The tri­

plicate test curves are reproduced for the 6.1% moisture con­

tent. Since the relative response in the triplicate penetra­

tions for other moisture contents performed with as good re­

produceability as the 6.1% moisture content case, only the

average of the three penetrations is reproduced in Figure 3

for the other moisture content conditions. As can be seen

for the 6.1% moisture content case, for a particular moisture

content and compaction, the variation between penetrations is

less than 2% from the mean value. This variation includes

both instrumentation response differences and differences due

e

140

130

120

110 -C\I ZIOO "'-al 90 -l -x 80

LLI Cl 70 Z

60 IJJ Z 50 0 (.)

40

30

20

10

0 0

e

STE ROSALIE CLAY S 0 IL

SOULANGES FINE SANDY LOAM

e

Data are the average of 3 penetrometer tests at each soil condition,

Infilividual teSTS were very close to the average.

1 1

1

.. ------ ..... , ... , ...... ~.. ... ...... "

' ---- 27% ' --- . / ------ ~ , ----

' ----1 ~ __ ..

1 6.1 %

SOll MOISTURE CONTENT

(WET BASE) "

:::::> 7-"'~ ...

h"'' 10. 6 0/0 1 l "'-"'" ~ 1 1 ......... _ 1 __ ... ______ _

1 .. __ - - - -____ 14 1 01 1"" .. -..... - _____________________ . 10 1 ..... __ ...

1 ... -- ... ---- ~2 501

1 - ... - - - - - _ _ . 10 1.1. ________________________ ~ " .. --:r· ... ~~ .... -.~-:.:::.==-=':.-=----=--=:.-:..--==::::=--------_____________ ~-_30.8 0/0 ,"--- ----------- .. - -- --------~r- . --::... 6. %

/ ~ ~-----------.------------------

J 2 3 4 5 6 7 8 9 10 Penetration de pth (inch)

FIG.3. SOll COMPACTION TEST: PENETRATION RESISTANCE VS. PENETRATION

w .-.,J i '

DEPTH FOR DIFFERENT VALUES OFSOIL MOISTURE CONTENT

...

38

to soil non-unifor.mities and experimental handling. For the

combination of probe, transducers and recorder, and soil

preparation used, this close agreement between repeat pene­

trations is considered to be very good.

For the purpose of this qualitative test, the com­

paction (which is defined as a soil reaction caused by the

application of mechanical forces in whiCh a reduction in

specifie volume of the soil oceurs (A.S.A.E., 1969, p. 292»

was measured as the percentage reduction in total volume.

The compaction results are given in Figure 4.

From these tests, it was found that the laboratory

compacted soil is quite different from the natural field soil.

The curves in Figure 3 show that for laboratory soil, the

resistance to the penetration increases with depth, at the

beginning, but then remains more or less constant as the

depth increases beyond about three inches. However, for the

natural field soil (Figure 2), the resistance to penetration

increases continuously with the depth. This difference is

due to the laboratory compaction procedure which undoubtedly

gives more dense compaction near the surface where the hammer

strikes.

Appendix Tables 3 and 4 show that the moisture content

of the soil also has an influence on the amount of compaction

and soil penetration resistance. This is in accordance with

general soil findings (Yong and Warkentin, 1966). As the soil

e e e

40~[------------------------------------------------------------------------~

35

30

IJ.I 1 5 ~ ::) ...J g 10

5

c:,~ 'Y,

~v'Y, ~ot::J

SOULANGES F 'NE SANDY LOAM -•

,,~~

. "

Data are the· average of 3 . compo'cti'on·· . tests at each ,J'"

soil condition. Individual tests were very close'" to the average.

01 , i , •

o 10 20 30 40 SO IL MOISTURE CONTENT (% ... W. B.)

FIG.4. ·THE EFFECT OF SOIL MOISTURE CONTENT ON SOIL

COMPACTION

'w, :\0: \.- ~

40

moisture content decreases, the penetration resistance of the

soil increases. However, for clay soil, at a moisture con­

tent (wet weight basis) above 35% and for the sandy loam above

15%, there is almost no Change in the penetration resistance

with moisture content. This phenomenon seems to be associa­

ted with the fact that the clay soil was almost saturated at

35% moisture content and the sandy loam has water films around

soil grains above 15% moisture content.

From Figure 4 it can be seen that for sandy loam. com­

paction increases with moisture content, but at 15% moisture

content there is no Change in the compaction. For clay soil

the compaction, at first increases,with moisture content, but

then decreases as the moisture content increases compaction

being highest at moisture content 23% for clay and 16% for

sandy loam.

It is realized that these compaction tests give only

qualitative results, as the calculation of the percentage com­

paction used assumes that the initial soil placement in the

compaction Chamber produces a unique density for its particu­

lar moisture content.

These compaction tests did show that for a particu­

lar compaction procedure and soil moisture content duplicate

and triplicate penetrometer passes gave very close results.

41

5.1.2. Water Infiltration Test

A test was conducted to determine the relationship

between soil water infiltration and penetrometer readings.

The tests consisted of inserting metal boxes, 4 feet x 2 feet

x 1 foot, into field clay soil to a depth of six inches as

indicated in Figure 5.

Water was added to these boxes to a depth of 1, 2

and 3 cm, respectively. Six penetrometer runs were made in

each of four boxes at eaCh of the three water addition

treatments at one-hour intervals for five hours after adding

water. The boxes were moved to adjacent undisturbed soil

locations for each of the three water addition treatments.

The results of this experiment are shown in Figure 6

for one hour after the water was applied. The results of

penetration runs at the end of two, three, four and five

hours were almost identical with the one-hour readings.

For the same depth, the penetration resistance is

found to decrease with an increase in soil moisture •. The

abrupt change in penetration resistance is probably associ­

ated with the depth of wetting front. The lack of differ­

ence with time is probably an indication that the top soil

had a high hydraulic conductivity and that translocation of

water was nearly complete one hour after the water was added.

42

7#~~#N~P~M~~~fi~ 1 1 1 1 L _________________________ J

If'------- + .... -------.,1

F/ ~ ;ri

~.:~Qr~~~ ~~~~~~~ 1

" ~

FIGURE 5. WATER INFILTRATION TESTER

e

260

240

_ 220 N

~ 200 ..... III 1 80 -J -x 160 LLJ o 140 z

12 0 LLJ Z 100 0 ()

80

60

40

2 0

0 0

e

measured one hour after pouring water

Curves given are the average of 24

penetrat Ions, 6 in each of 4 repllcates .

Individual penetrations were very

similar for any one water

condition,

2 :3 4 5 S 7

dept'h of penetrdtion (Inch)

8 9 10

FIG.6. THE INFLUENCE OF SOll WATER INFilTRATION ON THE CONE

PENETROMETER READINGS

e

Il

,J::. w

44

As shown in Figure 3 for the clay soil, the pene-

tration resistance is almost negligible for a moisture con-

te nt above 35%. This is in accordance to many research

studies (e.g. Yong and Warkentin, 1966), which have found

that at saturated moisture conditions, the soil friction

and adhesion between particles is practically nil because

actual particle to parti cIe contact is only established

through layers of water.

It can be seen from Figure 6 that the curves change

slopes at the wetting front. As a result, after irriga-

tion or after the rain has fallen, one can find the depth

of infiltration of the wetting front simply by taking

penetrometer readings and noting the point where a sudden

increase in readings is registered.

5.1.3. Bulk Density - Cone Index Relationship

The following analysis is used to predict the bulk

density of soil from a knowledge of the cone index. The

wet bulk density increases with the a~ount of moisture as

has been found previously (W.E.S., 1964), and it also increases

due to compaction of the soil underneath the paths of the

tractor. It also directly affects the soil bearing capa-

city (Terzaghi, 1959).

45

The sei1 samp1es for the wet bu1k density (grams wet

soi1/cc of field volume) were taken fram each tractor test

area where the penetration resistances were measured.

These resu1ts are shawn in Figure 7.

For clay soi1, the relation between bu1k density and

cane index is different for every cone penetration depth,

but for sandy loam soi1 the depth of penetration has no

effect on the cone index - bu1k density re1ationship.,

Thus, Gill (1967) has suggested that the cone index

has an advantage in the sandy loam soi1 and the specific

resistance appears to have an advantage in the clay soi1.

Because a basic cone-soil interaction in a compactib1e soil,

such as clay soi1, results in a compact ion of the sail in

the path of the cone, the penetration resistance increases

with depth above the zone of saturation.

For the clay soil used the bu1k density cannot be

predicted by cone index a10ne but it can be predicted by

knowing both cone index and depth of penetration. The

1inear regression equation expressing the re1ationship

between cone index and bu1k density for the clay soi1

measured is:

Bu1k density (gr of wet soil/cc of field soi1)

= 0.0049 (c.i.) + 1.1283 : at 3 in depth

= 0.00074 (c.i.) + 1.3953: at 6 in depth

o

47

and for the sandy loam soi1 is:

Bu1k density = 0.0006476 (c.i.) + 1.67195

Since this test was not done on other clay soi1

types this specifie resu1t app1ies on1y to the ste. Rosalie

soi1 used. It is suspected that the princip1e will app1y

to other clay soi1s. Testing this property with other soi1s

might 1ead to usefu1 genera1 resu1ts.

5.2. Trafficabi1ity Test

5.2.1. No Load Traction Test

Penetration resistance curves in relation to the

tractor performance are shown in Figure 8. Mobi1ity 1imit

1ines for the sandy loam and clay soi1s are found to be

quite different and are shown ïn Figure 9.

The minimum penetration resistance curves from the

series of six curves drawn in Figure 2 were chosen to plot

the graphs in Figure 8. Because the immobi1ity phenomenon

depends main1y on the softness of the soi1, the minimum and

not the average penetration resistance curve was used.

For farm land, which is usua11y cu1tivated to a depth

of about four to eight inches, the critica1 soi1 depth for

cone index was observed to be between two inches and six

inches. Be10w the six inches depth, the soi1 is more

C)

()

50

compacted and the penetration resistance and soil strength

begins to increase faster with the depth. It is also diffi-

cult to evaluate the original strength of the soil at a

level less than 1.5 inches below the soil surface because the

top of the cone is about 1.5 inches long. A good reading is

obtained only when the full length of the cone (1.5 inches)

is below the soil surface.

From the full curves of cone index versus depth

given in Figure 8 for locations on the ste. Rosalie clay

soil giving different amounts of slip, cone index values

for depths of two, three, four, five and six inChes were

obtained and plotted against percentage slip in Figure 10.

From this Figure it can be seen that the data for cone

index at the four-inch depth fit much more closely to the

smooth estimated curve than do the data for other depths.

From this, it is concluded that a single cone index value

at a four-inch depth gives the best relationship for esti-

mating slippage from a cone index reading. At the optimum

depth (four inches) the relationship between the tractor

performance and cone index can be indicated by the follo~ing

equation:

slippage = 481.053-26.19 (c.i. )+0.478 (c.i.)2-0.00283 (c. i. )3

The curves .in Figure 10 change slope at about 25%

F Iri . ;j:;+i .

~r ·H Fil

li !~!~:t!f !:ii ~tf1

. '+1:;-::

:F t,1 . H~ .

H·

.' ~*~H~!it! or.

:Iit

ml· EHl

';:;:i

o

52

slippage. This appears to be a property for rubber tires

on soil. It is noted that in the Nebraska tractor tests,

the pull at 15% slippage is taken to be the maximum pull for

the tractor. This was partly decided because tires wear

severely on the concrete test track. This slippage criteria

might be extended to 25% for lugged rubber tires on field

soils.

Immobility on clay and sandy loam soils generally

depends on the amount of sinkage of the tractor wheel.

Actual observation on the farm showed that sinkage is 'partly

due to vertical sinkage and partly due to slip sinkage con-

firming observations reported by Onafeco and Reece (1967).

This sinkage and slippage'relationship is similar for both

sandy loam and clay soils (Figure Il).

For no-go conditions, it can be seen from Figure 9

that for the same sinkage depth the penetration resistance

of the soil is greater in sandy loam than in clay soil.

These curves can be formulated as follows:

for clay soil (good for 2 inches-7 inches depth below surface)

Cone index at d inch depth = 3.6 (d) + 8.5

for sandy loam (good for 1 inch-9 inches depth below surface)

Cone index at d inch depth = 1.57 + 4.05 (d) - 0.237 (d2 )

: '

"

, i:; ~':

• 1. :

[Of '

54

In clay soil, the tractor wheel is more easily made

to spin than in sandy loam soil because of the interaction

of clay soil and the tire treads. At a sinkage depth of

about four inches it was observed that the clay soil filled

the spa ces between the treads making the tire appear smooth.

This condition also depended on the surface condition, the

soil moisture and organic content. But in the sandy loam

soil, the spaces between the tire treads are not completely

and readily filled with soil because the ad~erence of sandy

loam soil to the tire is not as great as that of clay soil

to the tire. In this series of tests, spinning only began

wh en the spaces between the tire treads were completely

filled with the sandy loam soil at a sinkage depth of about

six inches. Most of the theoretical work done by Leflave

(1966) and Masuta (1966) shows that sinkage varies linearly

with slippage, contrary to the curve obtained in Figure Il

which rises rapidly as the depth of sinkage increases, beyond

approximately five inches. The equation of this curve was

found to be obtained in the following:

slip (%) = 21.50 - 15.18 z + 3.90 z2

where z is wheel sinkage (inches).

These observations apply to a spring time field

condition. When the soil had been wetted to field capacity

or more right down to the water table and the soil was

beginning ta dry out from surface evaporation.

5.2.2. Maximum Drawbar Pull Test

This test was conducted on the ste. Rosalie clay

and Soulanges fine sandy loam soils to find the relation­

ship between penetrometer resistance and tractor drawbar

pull.

55

From the results of the test, as shown in Figure 12

and 13, the maximum drawbar pull capacity can be found from

the penetration curves. These curves for different towing

loads as shO~ln in Figures 12 and 13 are drawn from penetro­

meter readings obtained at the point where the tractor

wheels started spinning. From these curves it can be seen

that for any particular penetrometer depth a high cane

index value fits with a high drawbar pull ability. This

agrees with the traction theory whidh says that soil thrust

depends on the soil.

Cone index values for depths of two, two and a half,

three, four and six inches were obtained and plotted against

drawbar pull (lb) in Figures 14 and 15. From these figures

it can be seen that the data for cane index at two and a half

inches depth fit much more closely to the smooth estimated

curve than do the data for oLher depths. From this analysis

l.i n:

. En

;; W;i t!l E rijfr. ,

tIrJTI i~V '

~ ~

-._"-_." -----_.-

e ._-.

~i I~ l. '

-;_._----- -- : /.: ~ .. -;r::~'-.~-:--------. . ..JGu,! . l' ----. ' . . ,',' 1'------

["­

ln .... , ,",

., ') ,'"

.1/.\"

:ie'l .: L "]

icJI ~·r~. ,

li .. '.~ ~ ... ".: 1 . _. 1 :;., ,.

! : ::. '.~ :.-':'f:···'I' l' :--:. 'ri 1'>.:1 :' l' ... "., l'r._ 1,:--,:,,;---:-; ':r u , 1

Il .• j~::;g ... :

'.~. • > :,- 1:. -~~:, .l. ~ ::. '1

l ' . '1 .. , ; . ; :;' . ! . 1 ~'.j . :. .

f, ~". -~-1:··· ':"j:-i:: '.',' 'l' . ... . . .. i : ~. ..' : :. '. . 1::,:. 1 . " :, ..•... ,.

r ", '. ", L'I 1 '··· •• '· •• l~~~!l:, 1 •• •· .•••• -; •• ;,· 1 .. .<: ! .. ' i . _.- :' .. --i~' 1:' .,!

, 1 l,

:;.'

,. ,

,

r·. v

'i ~,".'" i, ";; " J,' , ., '/: : .. '

:!' V!,:;' . """ ',' . . ' .." ," 1, , '. '

.. l' " l" , ., ' • .' ' r . , . . "

" ' .. :. .Hi IJ:>p4·~L.I~f;-f/··J,· i ,ii!: 1 i" . 1 .. ." ,!' , ,. i'" .,. ,. . l' -", i .. , i ' ' . '.'

' ... ' .. ' . ,./( .!< r i .>/1, .'. \ ,.,..1: .1; '1' :: , ..... 1 .. ch,; .. , . 'j' .. J' , 1·' •.. ,.1 .j .. " 1 . 1 • , .. ,.

1'; .. 1·. "'1 i.

'\. \~"

{'<;-'~'

.1 . '!'

t/i .1 .. :1 •.. ·.1.'·;.!·· , ..•... " · .. I·····i· " ,1 ;. ,~230a,,). Vii ...• J!.;}.~~{:;.i;' :" ... v,~;:J-;i:! ::;1_ ... ' ... , ., ......

1 . .+ ..... . .' r'i'+'" ,. ·1· ··.1 .1 ··1 l' .. , ... .,

~7 .. : .. ; ·f?-~JJ:j·.i-li.J·"···!(J! ","!"'irEl'r:~~~}+}"L-, ~~'" J'~~'T'" :.1' ;. 'i.e'",'" l':'';''-l'::'''~:l':-''~--~'' ::.~!.-(:-=-:r::.-":----1--1~O·O,:::t ,j .. :' , . l ,. l ".' __ . i' --1'"'' .... . ...... . " "' "1" " "Il'" //'G~~ .. l' '." ....... , ...... , ', .. "1"'" ~. " . .. ," ... 1·· .. )·1 -.--f~(Y! i..-; ...•. ~.': J;:c~ç~~~J'-"~~~:):! i~06~;,J ..••• ~~~. ,.' "" ., •. ' .••. ":c:~;"., .• L.r,I.:,:;I.",,,.k ..... L:::.'.· .1'· ..... ~ .• T.,!i,r '1"::':" ,'J:' L ' .' J:) ,",: i :;:;J,:.! ,::~:,:.':""J;=; '.' ::':1,:1':-

_ , ' , '.' .. '1 ",".' .1 ..•. '." 1 '1"""""" ' .. ' '·;·· .. 1· ""j' '''''1' """"1' ;.' '( :~ z:e~-o"lb!:"""';-' :; ". l,A. 'i'" ~.' ..... : ']":'::I:ll.:J,:::;.]:t1~r}i:hiA~C.1Jj1IY ,. ,., .. 1. 1'"'' .• '. 1" '. i" 1 . ,,'. "'1 .'".' .. 1· .... ,· 1 .. , .. , .........

1

. __ :-~l.~----:..:,-:_;,,--l: : '1":.:- :'1' :,,;' : "':. !.l'.!' 5 . ~ ... , .. , .• ,., ..... " '.,.'.: :.,,"."" •. , ".1'.,:;: .. ,' '·.i " . .-, .. 1-. :',", ',' : .. ' 1·.. :, ...... J ".' ... 6· [., . 1 • 1 .. , .. ,,,,,'''j " 1 ........ , . [. . [ ..i' '. 1 i' :.T.!"'· T"p

c4

o•i',à ,,(bl~' '.':'1 i, l' I:' l" 's,' " " .!':. : .,:.: .. ';'::' c: .~ . ,;. '. (

F"g',re leo c~ ... I., ... ! ':: .. ,'. ' .. i .• ,,1:, .. :. '. '.' "~Iept.ll (tuç:.,) • i .::.::1 /:1 '::1' ".".s,'.' •. 10 ... ·[ • 1 ?J p~"O.I •... O,.,ct., ... , ...... '.' .1.' 1 .".'.'. ,.'.' 1 .' '1 . ""1 . '1"''''' ·1-::::···· .... ·: .!' ., : l'~ .," ï .·c.:, 'j":' 1

...... J.J .. '.:C: rrcrt~-t"r;?( +iil' ~iif~feÙ ~."r: 1 :" C ~ 'f ,·1· :Fril

';'- i cT;);

1

._ .. .! __ ., .,. L~..J ... , s'!'ldy 10."; •.• 1 ':'U\1l drarloa',· p'dl:/' .,]" .;. • Le ,).. .. 1"'" r '" '1 . ........ " .. , ...•.. ,.:~.L ... ~. ~ ... :e ... l.:. ,."j:'J~~:1L::'t~g~ir[:rtf;~1;Ed

' , .;;iFF l~t\t :;1' "

, ,

, co;· ne; , !~! ;:1~:

e- !1! d:' Fi: +i'

je; 1 , ,

;:;;: ::: " "

ir. tH! , ll::i i:tl' :jY'W: "

:;tl: [jo 1

~ , " 1: : • 1.1

~' i

: :

: 1

j

,,1

':E : :;:;'

j:i"

i\i: :il il ~;:! ' :,i:i'

;.: j:!: li,:;

e!i l , 1

l ' 1 :; :3WrtlT ' ': :~:l!.iüilf ' if" F !~,

..: . "

1 :

60

it is concluded that a single cone index value at a two and

a half inch depth gives the best relationship for estimating

the maximum drawbar pull capacity from a cone index reading.

The maximum drawbar pull capacity for the soil condi-

tions used can be found from the following equation using

cone index (P.S.I.) for a depth of two and a half inches.

For clay soil

M.D. (C) = 0.0598 (c.i.)3 - 8.94 (c.i.)2 + 448.5 (c. i.) - 5162.88

For sandy loam

M.D. (S) = 0.048 (c.i.)3 - 6.8 (c.i.)2 + 319.2 (c. i.) - 2565.2

where M.D. = maximum drawbar pull (lb).

As a result of the various tests, the optimum pene-

trometer depth for cone index reading for a farm tracto"r is

found to be between two and a half and four inches. In

comparison, for military vehicles, according to the W.E.S.

vehicle cone index system, the optimum depth for cone index

reading is six inches. The difference in the two reading

depths appears to be due to the fact that for military

vehicles the cone index is correlated with 50 vehicle passes

and generally for natural soil conditions. For farm vehicles

on the other hand, the mobility index is correlated for only

one vehicle pass for minimum tillage or traffic, and due to

61

cultivation, for soft soil conditions. Sinceother critical

far;m vehicle mobility problems oceur in theharvest season,

it would be a useful extension of this work to correlate

cone penetrometer readings with vphicle mobility at harvest

time. A critical case would be corn harvesting where a '

tractor is pulling a corn picker and a loaded wagon. If a

two-row picker is used there will be a second pass of the

vehicles in a previous wheel track. Thus, six vehicle

passes might be considered. Required drawbar pulls and

cone indices could be measured.

62

VI. SUMMARY AND CONCLUSIONS

The results of the investigations conducted for this

thesis indicate the following conclusions concerning the use

of a cone penetrometer to obtain an index of farm vehicle

mobility.

1. The cone penetrometer must be power driven at, constant

penetration rate to give repeatable results. Hand penetro-

meters did not give repeatable results.

2. It was found that a cone index value at four inches ~

depth could be used to predict tractor immobility with no

drawbar pull. It was also found that a cone index value of

a depth of two and one half inches could be used to give a

reasonable prediction of maximum drawbar pull obtainable on

Ste. Rosalie clay and Soulanges fine sandy loam soils for

M-F 135 tractor.

3. The analysis curves of tractor performance (Figure 10)

slip versus cone index show a change in slope at about 25%

slippage. This appears to be a property for rubber tires

on soil. It is noted that in the Nebraska tractor tests, the

pull at 15% slippage is taken to be the maximum pull for the

tractor. This was partly decided because tires wore severely

63

on the concrete test track. The full load allowable slippage

criteria might be extended to 25% for lugged rubber tires on

field soils.

4. The cone penetrometer gave more consistent results on

fields in springtime when the soil was moist right to the

water table th an on soils wetted in late summer by irregular

rain or experimental watering. The spring condition gives

soil which is drier at the surface and wetter below while

the late summer rain gives a slippery surface with firmer

and dryer soil below.

5. It was found that the laboratory compacted soil is quite

different from the natural field soil. The penetration re­

sistance curves show that for compacted soil in accordance

with the A.S.T.M. designation, the resistance to the pene­

tration increases with depth at the beginning, but then re­

mains more or less constant as the depth increases. However,

for the natural field soil, the penetration resistance in­

creases continuously with the depth.

6. In these tests the no load tractor immobility cone index

curves can be indicated by the following equations:

for the ste. Rosalie clay soil

c.i. at Ud U inch depth = 3.6 (d) + 8.5

64

for the Soulanges fine sandy loam soil

c. i. at "d" inch depth = 1.57 + 4.05 (d) - 0.237 (d)2

and for the Ste. Rosalie clay soil, the tractor general per-

formance equations are as follows for the optimum penetration

depth of four inches cone penetration

slip (%) = 481.053 - 26.190 (c.i.) + 0.478 (c.i.)2 -0.003 (c. i. )3

The maximum tractor drawbar pull for a certain soil condi-

tion can be indicated by the cone index at the optimum pene-

tration depth of 2.5 inches

for Ste. Rosalie clay soil

M.D. = 0.0598 (c.i.)3 - 8.94 (c.i.)2 + 448.5 (c.i.) -5162.88

for Soulanges fine sandy loam soil

M. D. = o. 048 ( c. i. ) 3 - 6.8 (c. i. ) 2 + 319. 2 ( c. i.) -2565.2

where M.D. = maximum drawbar pull (lb)

c.i. = cone index at 2.5 inches depth (lb/in2 )

7. Soil bulk density (wet weight basis) also can be indi-

cated by a cone index. The cone index is dependent on the

depth for the clay soil but not for the sandy loam soil.

The bulk density-cone index relationships are as follows:

for clay at 3 inches depth

B.D. = 1.13 + 0.0048 (c.i.) (wet soil gr/cm3 )

at 6 inches depth

B.D. = 1.395 + 0.00074 (c.i.)

for sandy loam

B.D. = 1.671 + 0.00065 (c.i.)

65

(wet soil gr/cm3 )

(wet soil gr/cm3 )

8. It was found that the sinkage-slip relationship for farm

vehicles can be shown by the following equatiom:.

S = 21.5 - 15.18 (z) + 3.9 (z)2

where

S = slippage (%)

z = wheel sinkage (inch)

9. From the literature theoretical relations between cone

penetrometer reading and commonly used soil properties such

as undrained shear strength, unconfined compressive strength,

plasticity, soil moisture, etc., have not yet been adequately

elucidated.

10. It appears that a cone index can be used to determine

differences in soil trafficability capacity. Since soil

moisture content had a considerable effect on the cone index

and the maximum drawbar pull, trafficability differences due

to drainage should be able to be indicated by the co ne index.

Since local moisture conditions at harvest time in a

corn field can be affected by run-off along corn rows to low

spots in the micro-relief a number of locations would need to

66

be tested to evaluate soil conditions at harvest time.

11. There appeared to be sorne relation between vehicle mobil­

ity and water table level, but it was not feasible in the

short time available in the 1969 spring to make sufficient

tests to obtain any definite relationship.

12. Vehicle mobility was adequate to allow tillage to pro­

ceed on the clay soil at soil moisture contents too high for

satisfactory seed bed preparation. Thus it appears that for

clay soils, soil trafficability at harvest time is a more

severe limitation than at planting time.

67

VII. RECOMMENDATIONS FOR FURTHER RESEARCH

1. It is desirable to develop a standard method for measur­

ing and relating vehic1e mobi1ity to the cone index for suCh

farm vehicles as tractor-cornpiCker combinations, grain com­

bines, forage and vegetab1e crop harvesters, instead of only

the tractor as used in this work.

2. Cone index is a composite property of the soil. Its

relationship to common1y used soil properties such as shear

strength, friction angle, unconfined compression strength,

cohesion, etc. needs to be more adequate1y e1ucidated.

3. From the results of this experiment the optimum depth

for cone index readings is genera11y sha110w (2.5" -. 4.0"),

and sma1l differences in co ne index affect vehicle perform­

ance a great deal. So, it is advisab1e to test other pene­

trometers with other angles and base areas with constant

speed of penetration to determine whether more reliab1e pre­

diction is feasible.

4. Domier (1968) suggested that the advantage of four wheel

drive or dual tires depends on soi1 conditions. It is desir­

able to define the soil trafficability in terms of cone index

for farm vehic1es' tire configurations.

68

5. A cone penetrometer might be used as a soil structure

measuring device. Sail conditions for germination and growth

of plants might be indicated by a cone index instead of by

bulk density. Aiso a cone penetrometer can be used ta mea­

sure the sail moisture content.

6. Cane penetrometers might be used ta indicate some physi­

cal properties of farm products such as grain, hay and si1age.

Because those physica1 properties are difficult to measure

and also its procedure is more comp1icated.

7. A know1edge of the traction mechanics of the sail is

needed for the management, design and development of farm

vehicles. Traction mechanics which are related ta soil

strength and traction devices have sa far been described

in very general terms by most researchers (Persson, 1969).

This means that"no quantitative measure of the sail strength

is known, and so, a prediction of the traction or mobility of

a vehicle on a particular sail is not possible.

Thus, it is recommended that a study be made on the

effects of traction device contact area and thread configur­

ation on mobility and traction using the cane index ta de­

scribe the sail strength.

69

IX. REFERENCES

A.S.A.G. (1969). "Agricultural Engineering Yearbook rr by A.S.A.G.

A.S.T.M. (1964). IlProcedures for Testing Soil ll by A.S.T.M.

Bekker, M.G. (1945). "Proposed field soil testing device. rr

Nat. Res. Council of canada, Assoc. COmm. on soil and snow mech. T.M. No. 1, ottawa, Ont.

Bekker, M.G. (1955). uA system of physical and geometrical soil values for determination of vehicle performance and soil trafficability. Il Proc. Inter Serv. Symposium Stevens, Inst. of TeCh. and Duke Univ. Office of Ord. Res., Durham, N.C.

Bekker, M. G. (1956) . "Theory of Land Locomotion: the Mech­anics of Vehicle Mobility.1l The Univ. of MiChigan Press, Ann Arbor, Mi ch •

Bekker, M. G. (1960) • 1l0ff-the-Road Locomotion: Research and Development in TerrameChanics." The Univ. of MiCh­igan Press, Ann Arbor, MiCh.

Bekker, M.G. (1969). "Introduction to Terrain-Vehicle Sys­tems. Il The Univ. of MiChigan Press, Ann Arbor, Mich.

Bernstein, R. uProbleme zur experimentallen motor pfugmech­anik der motorwargen." 16: 1913 (original not avail­able), cited in Bekker, M.G. IlTheory of Land Locomotion. Il

Broms, B.B. and D.G. Broussard (1965). IlSe lf-recording soil penetrometer. Il Am. Soc. of Civil Eng. Proc. Vol. 19, No. 4200.

Clark, S.J. (1966). "Pneumatic tire meChanics of a trac­tive performance of single, dual and tandem tires on soil. Il Ph.D. Thesis, Purdue university.

Domier, K. W. and o. H. Friesen (1968). IlPerformance para- _ meters of tractors equipp~d with singles, duals and four wheel drive. Il C.S.A.E. paper.

Evans, I.C. (1948). "The measurement of shear strength of soft soils in the field. Il Soil Mech. Symposium, Mini­stry of Supply, London.

70

Evans, I. (1948a). "The measurement of the surface bearing capacity of soils in the study of earth-crossing mach­inery." Geotechique. Vol. 2, No. 1.

Freitag, D.R. (1965). "A di.mensional analysis of the per­formance of pneumatic tires on soft sail. Il Ph. D. Thesis, Arburn, Alabama.

Freitag, D.R. (1967). IIPenetration tests for sail measure­ments." A.S.A.E. paper No .. 67.:"·652.

Gill, W.R. (1967). Il'rhe influence of compaction hardening of sail on penetration resistance. 1I A.S.A.E. paper No. 67-651.

Gill, W.R. and Vanden Berg, G.E. in Tillage and Traction. Il

(1968). IISoil Dynamics U.S.D.A. Hand Book No. 316.

Hegedus, E. (1965). IIPressure distribution under rigid wheel. Il A.S.A.E. Trans. Vol. 8: 3.

Housel, W.S. (1935). liA penetration method of measuring sail resistallce. Il Am. Soc. for Testing' and Materials. 35: 472-490 (1935).

Jo-Young Wang and A.R. Reece (1967). IIprediction of rigid wheel performance ba.sed on the analysis of sail wheel stress. Il Jour. of Terramech. Vol. 4, No. 1.

Keen, B.A. and G.H. Cashen (1932). of sheep folding on the sail." 22: 126-134 (1932).

IIrrhe physical effect Jour. of Agr. Science,

Knight, S.J. (1962) and Freitag, D.R. trafficability characteristics. 1I

5: 121-124, 132.

IIMeasurement of sail A.S.A.E. Trans.

Kondner, R.L. (1962). liA penetrometer study of the in situ strength of clays." Materials Research and Standards. March, 1962. pp. 193-195.

Leflaive, E. (1966). IIMechanics of wheels on soft sail. A method for presenting test results." Jour. of Terramech. Vol. 3, No. 1.

Liston, R.A. (1965). IIrrhe land locomotion laboratory." Jour. of Terramech. Vol. 2, No. 4.

71

Masuda, S. and T. Tanaka (1966). ItTraction of the tractor based on soi1 parameters. Il Proc. 2nd Inter. Conf. of Inter. Soc. Terr-vehic1e System, Quebec.

Mathieu, A.L. and J.A. Toogood (1958). liA se1f-recording soi1 penetrometer. Il Canada Jour. of Soi1 Sci. Vol. 38, 100-102.

McKibben, E. G. (1940) and D. o. Hull. ItSoil penetration tests as a means of predicting rolling resistance. 1I

Agr. Eng. Vol. 21, No. 6.

McRae, J. L. (1967). ItTheory for a powered whee1 in soil. Il Jour. of Terramech. Vol. 4, No. 3.

Mick1ethwaite, E.W.E. (1944). IISo i1 mechanics in relation to fighting vehicles. Il Mi1itary Col1ege of Science, Chertsey (original not avai1ab1e), cited in Reece, A.R. IIThe principles of soi1-vehic1e mechanics. 1t

Nicho1s, M.L. (1923). ItAn analysis of soi1 dynamics factors affecting the operation of tillage and tractor machin­ery.1I A.S.A.E. Trans. 17: 174-184.

Onafeko, o. and A.R. Reece (1967). mations beneath rigid whee1s. 1t

Vol. 4, No. 1.

IISo il stress and defor­Jour. of Terramech.

Persson, S.P.E. (1966). "Parameters for tractor wheel performance." A. S.A.E. paper No. 66-142.

Prather, O. C., J. G. Hendrick and R. L. Schafer (1968). ItAn e1ectronic hand-operated recording penetrorneter." A. S.A.E .• paper No. 68-518.

Proctor, R.R. (1933). "Description of field and 1abora­tory methods." Eng. News-Record 3 (10), 286-289, 1933.

Reece, A.R. (1964). "Prob1erns of soi1-vehic1e rnechanics." u. S. Army Land Locomotion Lab. A.'r.A. C. No. 8479, Warren, Mich.

Reece, A.R. (1965). Itprincip1es of soi1-vehic1e mechanics." Proc. Vol. 180, Part 2A, The Institution of Mech. Engrs., London.

72

Richards, S.J. (1941). liA soil penetrometer. 1I Soil Science Soc. of Am~ Proceeding, Vol. 6, 104-107.

Rush, E.S. (1967). Il Trafficabilit y tests with a two-wheel­drive industrial tractor. 1I A.S.A.E. paper No. 67-607.

Rutledge, • L. and F. V. Ma cha rdy. (1968). lIr.rhe influence of the weather on field tractability in Alberta. Il C.S.A.E. Journal, No. 2, Vol. 10, pp. 70-73. 1968.

Schuring, D. (1966). "The energy loss of a wheel." Proc. 2nd Inter. Conf. of Inter. Sco. Terr-vehicle System. pp. 391-424. Quebec.

Shuman, F.L. (1965). "A similitude study of soil strength instrument. Il Ph.D. 'rhesis, Iowa State Univ.

Sitkei, G. (196l). "Sinkage and rolling resistance of wheels on loose land. 1I Proc. lst Int. Conf. of Inter. Soc. Terr-vehicle system. Turin, p. 377.

Smith, J.L. (1966). "A study of the effects of wet surface soil conditions on the performance of a single wheel." Jour. of TerrameCh. Vol. 3, No. 2.

Soltynski, A. (1963). IISlip sinkage as one of the per­formance factors of a m.odel pneumatictyred vehicle." Jour. of Terramech. Vol. 2, No. 3. 1963.

Stone, A.A. and williams, I.L. {1939}. "Measurement of soil hardness." Agr. Eng. 20: 25-26. 1939.

Taylor, J.H. and G.E. Vanden Berg (1966). "'rhe role of displacement in a simple traction system." A.S.A.E. paper No. 65-122. st. Joseph, Mich. or Jour. of Terramech. Vol. 3, No. 1. 1966.

T.B. Eng. 37 (1959). "Soil Trafficabilityo" Dept. of the Army Tech. Bull., Washington, D.C.

Terry, C.W. and C.S. Winkelblech. (1968). "Hydraulic soil penetrometer indicates physical conditions." New York's Food and Life Sciences, Vol. 4.

Terzaghi, K. (1927). "Determination of consistency of soils by means at penetration test." Public Roads, 7: 240-247.

73

Terzaghi, K. (1959). "'rheoretical Soil Mechanics." John Wileyand Sons, New York, N.Y.

Tu, King Woo (1968). "'rhe effect of depth and spacing of subsurface drains." M.Sc. 'rhesis, McGill University,

Dept. of Agr. Eng. Uffelman, F. L. (196l). "'rhe performance of rigid cyl"inder

wheel on clay soil." Proc. lst Conf. Mech. Soil­Vehicle System, Turin.

Vincent, E.T. (196l). "Pressure distribution on and flow of sand past a rigid wheel. " Proc. lst Int. Vehicle­Terrain System, Turin. pp. 858-877.

W.E.S. (1947). "Trafficabilityof soil, pilot tests -self propelled vehicles." Waterways Experiment Sta­tion, T.M. No. 3-240, Vicksburg, Miss.

W.E.S. (1948). "Development of testing instruments." ~eCh. Memo No. 3-240. Trafficability of soils, 3rd sm;,. 66 p.

W.E.S. (1951). "Trafficabilityof soils, slop studies. Tech. Memo 3-240, 29 p. (1951).

W.E.S. (1963a). "Field moisture content investigation." Tech. Report 3-610. 1963. W.E.S., Vicksburg, Miss.

W.E.S. (1963b). "Environmental factors affecting ground mobi1ity." Waterways Exper. Station, No. 5-625, 1963.

W.E.S. (1964a). "Measuring soil properties in vehicle mobility research." W.E.S. T.R. 3-652, Vicksburg, Miss.

W.E.S. (1964b). IIstrength-moisture density relations of fine grained soils." W.E.S. T.R. 3-639, Vicksburg, Miss.

Wiendieck, K.W. (1968). "Stress-displacement relations and terrain vehicle mechanics: a critical discussion." Jour. of Terramech. Vol. 5, No. 3. (1968).

williford, J.R. and L.W. Larson. (1968). liA study of soil strength valuesincluded in cone index readings. 1I

A.S.A.E. paper No. 68-666.

74

Wills, B.M.D. and F.M. Barrett. (1965). "An investigation into rolling resistance theories for towed rigid wheel. " Jour. of Terramech. Vol. 2, No. 1. 1966.

Yong; R.N. and B. P. Warkentin. (1966). "Introduction to soil behavior." The Macmillan Co., New York. p. 451.

·Yong, R.N. and J.D. Fitzpatrick-Nash. (1968). "Drawbar pull prediction from energy losses in wheel-clay interaction." Soil Mech. Series No. 22. Soil Mech. Lab., McGill University. August, 1968.

Zelenin, A. N. (1950). "Basic physics of the theory of soil cutting." 353 pp. Moscow (1950) (ol.iginal not avail­able) from Gill and Vanden" Berg "Soil dynamics in tillage and traction.

APPENDICES

76

A. TERMINOLOGY

1. Bearing Capacity: The ability of soil to support a

vehicle without undue settlement of the vehicle.

2. Cone index: An index of soil consistency or strength.

It is the force per unit base area required to move a

30 degree right circular cone of 0.5 sq. in. base

area through the soil at a rate of 72 in. per min.

3. Drawbar pull: Force at the drawbar produced by the

vehicle in the direction of travel.

4. Maximum tractive effort: The maximum continuous towing

force or pull a vehicle can exert expressed as pounds.

5. Slip: Relative movement in the direction of travel at

the mutual contact surface of the traction or trans-

port device and the surface which supports it.Slip and

travel ratios are sometimes used synonymously, and are

frequently expressed in percent.

slip (%) = (1 - actual travel distance )x 100 theoretical travel distance

6. Soil shear strength: A function of cohesion between the

soil particles and intergranular friction. This re-

lationship can be represented as the culomb equation:

77

S = c + Ptan~

where S = shear strength (lb/in2 )

C = cohesion or shear strength when normal stress (P) is zero (lb/in2 )

P = intergranular stress normal to the shear surface (lb/in2 )

~ = friction angle between the soil particles (dimension-less)

7. Soil trafficability: A soil property which is the capa-

city of soil to support specifie vehicle action. It

is related to the vehicle mobility environment factor.

8. Thrust: Net traction, plus rolling resistance of trac-

tion device while pulling.

Tractive thrust~ the total force developed by a trac-

tion device in the direction of motion.

Soil thrust: Soil behaviour under the traction device

by which the soil resists the vehicle-tread thrust.

9. Tractive capacity: Ability of a soil to resist the

vehicle-tread thrust required for steering and pro-

pulsion.

10. Traction device: Any element of the vehicle (track and

wheel) that is in contact with the ground under nor-

mal motion.

78

Il. Tractive effort (force): force applied to a vehicle in

the direction of travel by a traction device and is

equal in magnitude to tractive thrust.

12. Travel ratio: Ratio of distance travelled per revolu­

tion of the traction device while pulling to the dis­

tance travelled perrevolution of the traction device

with zero drawbar pull on a concrete surface.

13. Vehicle mobility: A vehicle property which is the

vehicle movement ability.

14. Wheel sinkage: The depth to which the tire penetrates

the soil, measured relative to the original soil sur­

face.

79 B. DATA TABLES

Table 3. The effect of moisture content on soi1 compaction at 1aboratory soi1 test for fine sandy loam

ComEaction Moisture Content Depth Volume Change Depth for

% cm % Eeak, C. I.

2.7 5.6 12.25 3.2 in

6.1 9.0 19.69 2.3

10.6 13.5 29.73 1.5

14.1 14.8 32.37 1.4

22.6 14.5 31. 71 1.3

30.8 14.6 31.93 1.0

Table 4. The effect of moisture content on soi1 compaction at 1aboratory soi1 test for clay soi1

ComEaction Moisture Content Depth Volume Change Depth for

% cm % Eeak, C. I.

6 4.75 10.39 3.6 in

16 8.75 19.14 4.1

25 11. 75 25.70 6.0

32 9.70 21. 22 increase with depth

37 8.50 18.59 Il

B. DATA TABLES

Table 5. Bu1k density - cone index re1ationship

CLAY SOIL CLAY SOIL SANDY LOAM at 3 in de12th at 6 in.de12th

c.i. B.D. M.C. c. i. B.D. M.C. c. i. B.D. M.C. 21 1.203 44.2 33 1.391 37.1 44 1.688 34.13

25 1.250 43.1 44 1.450 35.6 47 1.695 32.35

35 1. 287 41.5 46 1.420 35.7 49 1.701 30.80

48 1.360 39.6 60 1.475 36.3 65 1.730 27.76

60 1.454 37.2 143 1.480 34.2 72 1.754 24.9

68 1.495 36.4 148 1.495 35.8 82 1.710 25.1

85 1.532 35.3 166 1.537 33.0 94 1.742 25.8

77 1. 555 34.0 191 1.530 32.4 100 1.720 25.4

89 1. 597 33.8 238 1.595 30.6 118 1.749 21.6

106 1.625 32.9 261 1.646 29.1 140 1.765 22.5

106 1.650 32.5 278 1.613 30.3 162 1.775 22.2

114 1.661 30.3 310 1.618 31. 0

119 1. 732 29.8 366 1.682 29.5

Cone index is average value of six series test curve.

M.C. is soi1 moisturecontent (%) of dry weight.

B.D. is soil bulk density or wet basis. (gr of wet soi1/cc of field soi1 Volume).

c.i. is cone index (lb/ln2 ).

De12th 3

3

5

7

9

3

5

5

7

9

9

81'

Table 6. Tractor performance with cone index on the clay soi1

Depth

1 2 3 4 5 6 7 8 9 10 Slip Test No. Incb~s %

1 1.5 2.5 4 4 5 6 7 7 8 10 100

2 2.5 6 8 10 12 15 18 21 26 74 100

3 6 Il 15 18 22 25 29 46 76 108 100

4 7 13 17 21 25 29 33 49 72 95 100

5 9 16 19 23 26 30 34 55 91 126 100

6 9 17 21 27 32 38 41 53 85 115 66

7 10 18 24 28 32 36 40 55 101 152 60

8 9 18 25 31 38 46 66 91 126 160 42

9 Il 20 28 34 41 50 56 66 110 165 27

10 8 16 24 38 55 83 132 184 25

Il 12 20 30 36 44 58 81 105 132 154 23

12 13 24 32 40 49 66 90 114 138 161 21

13 14 28 39 50 62 75 87 120 156 187 17

14 20 32 46 59 72 88 104 170 210 14

15 20 40 59 78 95 113 132 189 267 4

Sink in. 9.5

7.5

7.0

6.8

6.5

6.2

5.5

5.2

4.5

4.5

4.0

3.5

2.5

1.7

0.5

i82

Table 7. Whee1 sinkage - slippage re1ationship

Whee1 Sinkage Slippage Whee1 Sinkage Slippage (inches) (%) (inches) (%)

0.5 4* 4.5 25*

1.0 7 4.5 27*

1.5 Il 5.0 37

2.0 14* 5.2 42*

2.5 13 5.5 38

3.0 13.5 5.5 60*

2.5 17* 6.0 62

3.0 17 6.2 66*

3.5 21* 6.0 80

4.0 21 6.3 100

4.0 23* 6.5 100*

4.2 25 6.8 100*

*C1ay soi1. (ste. Rosalie clay soi1) Other data are from tests on Soulanges fine sandy loam.

! 83

Table 8. Maximum drawbar pull test - ste. Rosalie clay (Cone Index Values p.s.i.)

pounds Load Zero 1000 1300 2000 2500 3000

Depth 1" 9 10 Il 10 20 18 2" 16 18 20 24 44 52 3" 19 22 25 56 67 88 4" 23 29 32 94 102 130 5" 26 34 45 128 126 164 6" 30 43 65 180 150 228 7" 34 56 80 232 176 284 8" 55 69 9A 290 206 330

Table 9. Maximum drawbar pull test - Soulanges fine sandy loam

(Cone Index Values p.s.i.)

pounds Load Zero 1000 1500 1900 2300 3000

Depth 1 5 8 Il 14 20 22 2 9 13 20 24 35 60 3 12 16 22 28 39 82 4 14 18 24 31 42 91 5 16 20 25 33 47 98 6 17 22 27 35 50 105 7 18 24 29 38 56 110 8 19 26 32 41 59 128 9 19 30 35 44 62 159

COMPUTER PRO GRAM

Fortran subroutine for polynomial Regression IBM system 360 Scientific subroutine package (360A-cM-03X) Version III Programmerls Manual was used to obtain curves of best fit given in figures in this thesis.

84