MEASUREMENT OF passsunss IN SOILS
PRODUCED BY TRAFFIC AND'THE '

RELATIONSHIP BETWEENTHOSE messages.

AND COMPACTION IN UNDISTURB'ED sOILs f 7

. Thes—is foT the Degree Of Ph. D 7;
MICHIGAN STATE UNIVERSITY, g
Nathan Andrews wIIIIIs

1956 ' '

THESIié

 

LIBRARY

Michigan State
University
r _‘-l

 

This is to certify that the

thesis entitled

Measurement of Pressures in Soils Produced‘by Traffic
and the Relationship Between Those Pressures
and Compaction in Undisturbed Soils

presented bg

Nathan A. Willits

has been accepted towards fulfillment
of the requirements for

m degree in Mnce

Major professor

Date Almrlgi I? S'é

0-169

MEASUREMENT OF PHESSURES IN SOILS PRODUCED BY TRAFFIC
AND THE RELATIONSHIP BETWEEN THOSE PRESSURES AND

COMPACTION IN UNDISTURBED SOILS

By

Nathan Andrews Willits

AN ABSTRACT
Submitted to the School for Advanced Graduate Studies of
Michigan State University of Agriculture and Applied Science
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Soil Science

Year 1956

Approved by (j? ,L~.CE:T°%E?

 

 

 

Nathan Andrews Willits

AN ABSTRACT

The subject of soil compaction is of considerable current interest
to farmers and soil scientists alike. Research has already provided
some important information on how to manage soils to minimize the com-
pactive effects of tillage and traffic. Little has been done, however,
to investigate the more basic aspects of the problem. The study herein
reported was desigied to supply some of the much needed information on
the nature of the forces in soil arising from tillage and traffic and
how they may be affected by various soil and loading conditions.

A cell using strain gages was designed for measuring pressures in
soil. The cells were buried at varying but fixed positions beneath un-
disturbed soil. Various farm vehicles and implements were passed over
the cells. The pressures were recorded using a Hathaway lZ-channel
recorder.

Maximum pressures varied near the surface from over one hundred
pounds per square inch under the drive wheel of a Massey-Harris Clipper
carbine to twenty-five pounds per square inch under the rear wheel of
a Ferguson tractor. Tire lugs were responsible for considerable vari-
ability in the recorded surface pressures. The pressures diminished
rapidly with depth, but were measurable to a depth of sixteen inches.

Soil variables affecting the distribution of pressure under farm
vehicles include bulk density, texture, and moisture content. The
vehicle and its speed of travel were also important factors affecting

the pressure.

 

Nathan.Andrews'Willits

Pressure under tillage equipment was immeasurably small at a
depth of seven inches. Negative pressures of unknown significance
‘were recorded.during plowing and on other occasions.

'Field soils were compacted‘hy traffic. The amount of compaction
was neasured‘hy determining the bulk density using soil cores three
inches in diameter and three inches long. The vehicle, number of passes,
original soil density, and especially the soil moisture content were
variables fcund to affect the change in density (compaction) observed.

Cores of undisturbed soil were taken from.the same locations at
which the tractor compaction tests were made. These were compacted at
various pressures in the laboratory using a special compressed air-
driven apparatus. The pressure required to produce the same change in
bulk density in the cores as was effected.by the passage of a tractor
in the field was Obtained. This pressure was very similar to the

pressures recorded‘hy the test cells at corresponding depths.

 

 

MEASUREMENT OF PHESSURES IN SOILS PRODUCED BY TRAFFIC
AND THE RELATIONSHIP BETWEEN THOSE PRESSUBES AND

COMPACTION IN UNDISTURBED SOILS

By

Nathan.Andrews Willits

A THESIS
submitted to the School for Advanced Graduate Studies of
Michigan State University of Agriculture and.Applied Science
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Soil Science

Year 1956

' #:7'5’8‘
4 4W0 5’

    
  
  
  
  
   
  
  
  
  
  
  
  
   
  

ACKNOWLEDGEMENT

For his unflagging aid in providing counsel and exhortation,
and for unstintingly providing his time and resources throughout this
investigation and manuscript preparation, the writer is particularly
indebted to Dr. A. E. Erickson.

To Prof. P. J. DeKoning, who designed the test cell used in this

study, who made available the facilities for calibrating it, and who

 

rendered other valuable assistance on various occasions, the writer
wishes to express deep appreciation.

Grateful acknowledgement is also due Dr. E. A. Finney, Director
of Research, Michigan Highway Department and his associates Paul
Milliman and Gale Otto for providing and operating the pressure record-
ing apparatus; to Dr. F. W. Snyder for loaning the compacting apparatus;
to Dr. R. L. Cook, Claude Price, and the many other members of the Soil
Science Department who, at one time or another, contributed significantly
to the culmination of this study; and to Miss Catherine Bremen for her

patience in typing the dissertation.

ii

 

Nathan Andrews Willits
candidate for the degree of

Doctor of Philosophy

Final examination, May 18, 1956, 8:30 A. M., Room 210, Agricultural
Hall

Dissertation: Measurement of Pressures in Soils Produced by Traffic
and the Relationship between those Pressures and
Compaction in Undisturbed Soils

Outline of Studies

 

Major subject: Soil Science
Minor subjects: Geology, Physical Chemistry

Biographical Items
Born, May 8, 1923, Haddonfield, New Jersey

Undergraduate Studies, Rutgers University, 19141-19143 and
l9h6-19h8, Degas of B.S. in Agriculture, February 191:8

Graduate Studies, Rutgers University, l9h8-19h9, M. S. in Soil
Science, September l9h9; Michigan State University 1919-1951,
cont. 1953-1956

Experience: Research Fellow, Rutgers University l9h8-l9h9,
Instructor, Michigan State University, 1919-1955,
Assistant Professor of Soils, Rutgers University,
1955-

Member of Alpha Zeta, Society of the Sigma Xi, American Society
of Agronom, and Soil Science Society of America

iii

 

TABLE OF CONTENTS

MODIICTION esoeosooeoeooooeeeosoeoooosooeesoeeooeooosooooeeeoo
me REVIEW Oooeootooossoeoeseesoaotosses-oesseoosooouoono
HSWTION 00000-000000...soc0000000000...oeeeooooeeeneeoob
cell D8319 eoeooose-oeoeeeeooeeeo-essenceseoeeee0.000000...
031.1 constmction soso.none0.0esoseeeeeesosoesce-eeoeeosone.
cell calibration sseeosoeoesooeeasoeoeeoeeeooeoooeooees-oeoe
msme Recording 0.000000oneseeeeeoeeeesoo-osenses-oceans.

mmm .OODOOOOOOOOOCQCOOOOOOOOOOOOOOOOICCOOOOIOOIOUOOOO'....

Gel]. mate-113131011 .OOIOCOOOOOOOOOOO00.0.00...OOOOOCOOOOCOOOC

Soils 000000000000!0000000soseeeooseoooeoeoooeoseeesoseess-o
Pment Cocoooooooseoofiessosettoeooecoeeoeseoossees.one...

vehiCIe Cmaction .IOOQOOOOOIOOOOOOIOOOOOOOIOOOOOOIO00-0...
WITSANDDISQISSION .OOOOOOOOOIOODOOOOCOOIOOIIOOOOOOOOOOOIQOI
mmtude Of 8011 Pressure see-cocooooooeeooeoessence-cos...
vehicle effect 00.0.0.0...tOO0.0.0.0000...0.000.000.0000

Sci-l effects 0.0.0.0....0.000.000.00000000000'OOOOIOOCOO
Tillage implements effect ..............................
Pressure Distribution .......

8°11 comaotion 030.000.000.00000000Ioeoesoseoosesoooososno.

Field .‘QOOOCOOOOOOOO0.000......OIOIOOOOOOCOOOOI...0....

Laboratoz‘y 090000-00echoessesoeeosooooeooesosee00.000000
WY AND CONCLUSIONS .0000.-sGeese...soeeoososelloooooeoesloo

LITmAmRE 01m .OOOOOOOOOOOOOOOOOOOOOODOOOQOOCO005.00.00.00...

APPENDIX OOOOOIOOO00000000000000.0009essence-eooeeeeseoeoseocoss

iv

Page

 

LIST OF FIGURES
Page

fig‘lre I. Scale dramg Of load test cell oesoeoeooeoooocooeeeoo 13
Figure II. Photograph of soil load test cell .................... 1h
Figure III. Sample of a calibration curve ........................ 18

Figure IV. Scenes during installation and operation of soil
pressure measuring equipment ......................... 20

Figure V. Sample of a trace made by the Hathaway instrument .... 21

Figure VI. Instrument used to compact soil cores in the
labora‘wm 0.0I.0......0.0.0.000...OOIOIOOIOIOOOOCOICOO 27

 

Figure VII. Trace showing negative and residual soil pressures ... 36

Figure VIII. Relation between recorded pressure and the position
of the test cell with respect to the tire tread ...... 38

Figure IX. Isobars under rear tractor tire ...................... b?
Figure X. Isobars under rear truck tire ........................ ha
Figure II. Effect of tractor traffic on soil bulk density ....... 67
. Figure XII. Compaction produced by twentyAfive pounds per square
[ inch pressure on soil cores taken at a depth of zero
’ to three 11101168 .0.........OOOOOOOOOOOOOOO0.0.0.000... 7
Figure XIII. Compaction produced by fifty pounds per square inch
pressure on soil cores taken at a depth of zero
to was mohes ......OO.‘00.00.00.........OOOOOOODOOO 76
Figu‘ XIV. Compaction produced by twenty pounds per square inch

pressure on soil cores taken at a depth of four
to seven inches soo-ooooooseeooesoooooeoeoooooooooo-oe 77

 

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Table 1.

Table 2.

Table 3.
Table h.

Table 5 0

Table 6.
Table 7.
Table 8.
Table 9.

Table 10.

Table 11.
Table 12.
Table 13.
Ends 1h.

Table 15,

 

LIST OF TABLES
Page

Pertinent data of equipment used in load test
Studies on severaJ. SOilS 0.0.000...Oeolooeeooooeeossseos 2).].

Some physical properties of soils compacted by traffic.. 26

Maximum and average soil pressures obtained at various
depths under several vehicles, l95h .................... 31

Maximum and average soil pressures obtained at various
depths under several vehiCles, 1955 ooooooeoseoooeooeose 3’4

Variability in recorded pressures from two passes
with Ferguson tractor rear tire at varying distances
from cell ......OOOOOO0.0.0.0.......OOIIOOOOOOCOOIOOOOI. 37

Effect of vehicle speed on average soil pressures in
Hfllsdale sarldy. 10m ......OOOO...IOOOOOOOOOOIOOOOOOOOOO 39

Pressures at various depths under an empty and loaded
Ford one-ton piCkuP thk eeeoeooooooeeeoooscoooooooooso ’40

Maximum pressures in some soils at different moisture

contents 0000000000000000000000000.0000...Iaoeeoeeelone. 2

Maximum soil pressures_in disturbed and undisturbed

80118 .0000Onooooootoeeaooesose00¢...Coosoeessoeeseno... ’43
Pressures associated with passage of tillage implements. hS

Maximum pressure at a depth of three inches as
measured by a test cell in a horizontal position........ 50

Bulk density of Sims sandy clay loam resulting from
field and laboratory compaction ooso-eessooeoeoo-eoeeoeo 53

Bulk density of Conover loam resulting from field
and laboratory compaction .............................. 56

Bulk density of Berrien sandy loam resulting from
field and laboratory- compaction eeeooeoeosoaonseeeooOboo 58

Bulk density of Hodunk sandy loam resulting from
field and laboratory compaction ....ooooeoosooeeoosoouoo 60

 

 

 

:07.

fie-

Table 16.

Table 17 .

Table 18 .

Table 19.

Table 20.

Table 21.

Table 22.

Table 23 0

Table 2h.

Table 25.

Table 26 .

Table 27.
Table 28.

Thble 29.
Table 30 .
Table 31.

Thble 32,

LIST OF TABLES (continued)

Bulk density of Hillsdale sandy loam resulting from
field and laboratory compaCtion ...-Osoosoeoeeoosoceoos

Bulk density of Brookston loam resulting from field
and laboratory compaction .............................

Bulk density of Conover loam (Site 8) before and
after compaction .C......‘O..............O......O.."..

Effect of moisture on soil bulk density with traffic
fiom Ferg‘lson tractor ......OOIOOIOCOICIOIIOOOCIOCOI...

Bulk density of soils when compacted at two depths
by a Ferguson traCtor ..IOOOOOIOOOOOOOOOOOOOOOOOOOGOOOO

Compaction produced by truck and tractor . . . . . . . . . . . . . .

Change in bulk density of Brookston loam due to
traCtor traffic O.......OOOOOOOOOOOOOOOIO0.00.00.00.00.

Effect of initial state of compaction on the change
in bulk density with applied pressure .................

Effect of lubricating the inside of soil cores at
the time of sampling on the compaction produced by
applied pressure oesoesosoosooososeesooesoooeeoosossoo.

Effect of number and length of time of application
Of pressure to 8011 cores oooeoeoeeseseoocececeooeeoooo

Pressures required to produce the same compaction in
soil 'cores as was produced by Ferguson tractor traffic.

Sample copy of tabulation sheet .......................

Summary of loads recorded on Hillsdale sandy loam,

June 195h .............................................
Summary of loads recorded on Hillsdale sandy loam . . . . .
Summary of loads recorded on Sims clay loam . . . . . . . . . . .
Summary of tillage data, August, 1951; .................

Summary of loads recorded on Plainfield sand . . . . . . . . . .

Page

62

63

6h

65

68
69

70

71

73

7h

79

87
88

92
93

 

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LIST OF TABLES (continued)
Page

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‘ Table 33. Sumuary of loads recorded on Hillsdale sandy loam ..... 95

Table 314. Summary of loads recorded on Sims sandy clay loam ..... 96

Table 35. Summary of loads recorded on irrigated Sims sandy
clay loan .....OOOOO0.00IOOCOCOIOIOOOOOCOOIOOOOIIOOOUO. 97

Table 36. Summary of loads recorded on irrigated Spinks sandy

IOWOOCOOOOOOOOCOOOOOCOIOOOOOOOOOOOOOOIOOOOOUOCOOOCOCI. 98

Table 37. Smmnary of loads recorded on Spinks sandy loam ........100

viii

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INTRODUCTION

Traffic compacts soils. Agriculture is now mechanized in America

as in no other country of the world. This mechanization has undoubtedly
helped the national economr in that fewer farmers are now producing more
and better quality food and fiber than ever before, but with the bene-
fits of farm mechanization problems have also come. One of these prob-
lems is compact soil. It would be serious enough if the zone of
compaction was restricted to the top six inches, but there are many
areas where soils have compacted layers deeper in the profile. "It is
eVident that farm tractor operations may compact soil below plow depth
When draft loads are greater than or equal to those used in pulling a
two-bottom plow," report Jamison et a1. (16) as a result of extensive
tests with a Cecil clay soil.

Each year manufacturers introduce bigger and heavier machines.
One company now has an experimental model which weighs eight tons.
Several pieces of equipment weighing over 10,000 lbs. are now commer-
°1ally available. With heavier units larger sized tires are being used
80 that the load per square inch will not be increased, but the area of
3°11 being compacted is increased. Perhaps the most important cause of
80211 compaction is the fact that farmers are relying more on machinery
in their operations and are making more trips across the land in the
n01'mal care of a crop. Weaver (us) states that in cotton farming a
re“ wheel could conceivably pass over a given location twenty times per

yea-1‘ from plowing to harvesting, using tractors for all operations.

-1-

Compacting soils results in a decrease in the size and amount of
voids. This causes decreased percolation and aeration, and limited
storage capacity for available water. This effect upon moisture and
ongen supply may well prove ham to root growth and ultimately to
crop yields. Soils may become so dense that they provide mechanical
impedance to the growth of the apical portion of the root. This of
course results in a limited rooting zone. Results of one investigation
(13) have indicated that root growth tends to be greatly restricted in
certain fine-textured soils when the bulk density exceeds 1.145. Crop
yields in coarser textured soils fall off rather rapidly if the bulk
density exceeds 1.55 (1:5). Whether the actual cause of poor root growth
in compacted horizons is low porosity or high bulk density is difficult
to determine, for the conditions that bring about mechanical resistance
to penetration of a soil horizon by roots are unavoidably, and perhaps
inseparably, associated with undesirable moisture and aeration charac-
teristics.

Compact soil layers may be genetic in the sense of having formed
during, and as a part of, the present cycle of weathering and soil forma-
tion. The compact horizons may also be relics of earlier cycles of
1'Gathering and are thus a part of the 3011's parent material. such com-
Pact layers most frequently are encountered below the root zone, and,
although probably affecting the moisture regime of the profile, do not
necessarily impede root development.

Of more particular concern to farmers and agronomists alike are

“1080 compact layers which occur near the surface of the soil. Many of

these layers have only recently been formed, presumably due to tillage
operations. Intensive farming operations leave the soil in poor tilth.
The increased traffic per rotation coupled with the decrease in organic
matter results in gradual compaction. Compaction may be so slow that
a "traffic pan" can develop before a farmer is aware of it.

Soil moisture content and particle size distribution are important
soil characteristics affecting the susceptibility of a soil to compaction.
Highway and construction engineers were probably the first to point out
these relationships. Mbst frequently, however, these workers were deal-
ing with soil materials whose properties were quite dissimilar to those
of the surface soils used in agriculture. Thus, the conclusion of the
engineer may not always hold when applied to agriculture. Furthermore,
the objective of the engineer was to produce a compact soil; the oppo-
site is true in agriculture, "prevent compaction" being the by-words.

Research in agriculture has corroborated the findings of the
engineers and has further shown, using bulk density or penetrometer
measurements, that land resting and rotations including sod minimize
the compactive effects of tillage. Little effort, however, has been
made to date to evaluate the sources or the forces responsible for soil
compaction, or the soil properties which resist or augment such compac-
tive effort.

With the advent of heavy farm machinery there has arisen, fortunate-
ly, an increasing consciousness that soil compaction problems exist. At
the l95h annual meetings of the Soil Science Society of America a sympo-

sium was held on soil compaction. The Tillage Machinery Laboratory of

the United States Department of Agriculture is expanding its research
on problems involving soil compaction, but much fundamental research
is needed. The present knowledge of the relationships between tillage
operations and soil compaction is quite meager.

The study herein described was initiated with the hope that some
contribution useful to a solution of the soil compaction problem would
be forthcoming. The main objective was to measure the pressures in
undisturbed soils, resulting from passage of various pieces of agricul-
tural equipment, under a range of soil texture and moisture conditions.
Such information should provide a clue as to whether compaction caused
by tillage is due to the tractor traffic or to the cultivating tool.

Investigation of the factors that influence the extent to which
traffic affects soil compaction was also included. Further, it was
envisioned that if soil cores could be compacted in the laboratory,
then the pressure necessary to produce a compacted condition equivalent
to that formed by traffic could be known. Such information would be
useful in establishing the reliability of the pressure cells and in

dehumdning in an easy manner the susceptibility of a soil to compaction.

LITERATURE REVIEW

As early as 1929 Bacon (2) called attention to the fact that undesir-
able compaction might result from tractor wheel traffic. However, soil
scientists in those days were so busy investigating chemical relationships
of soils that little attention was paid to any possible effect that farm-
ing practices might have on the 5011's physical condition. Furthermore,
about that time the classical work of Nichols (21) showed that the aver-
age pressures exerted in the soil by a plow were small.

Perhaps the compactive effects of tractors were not so great 25
years ago. The farm tractor population was less than 20 percent of what
it is today, and most units were equipped with steel wheels. Studies
at the THJlage Machinery Laboratory of the United States Department of
Agriculture (25) have shown that tractor wheels equipped with steel lugs
compact the soil about ho percent less than those equipped with rubber.

That compaction is taking place in many soils today there can be
no doubt (6), (11), (19). Although the limits to which a soil can be
compacted and yet not adversely affect crop yields have not been worked
out, except in an extremely general way (h5), it is certain that present
agricultural equipment and practices are rapidly causing such a limit
to be approached in some soils.

The amount of compaction taking place in a soil is dependent upon
two things, viz. the physical properties of the soil and the character-
istics and operation of the compacting piece of equipment. The soil

properties which are involved include texture, pore space, moisture

-5-

content, and.amount of organic matter. The applied load, size, construc-
tion, design, and inflation of tire, and speed of operation are some of
the other factors affecting soil compaction.

Free, et a1. (12) and.Russell, et al. (29) have shown that soils
amply supplied with Organic matter are much less susceptible to compac-
tion.

Jamison, et a1. (16) and'weaver and.Jamison (h7), working on dis-
turbed soils at the Tillage Laboratory, found that the compactibility
of soils generally increased with increasing moisture content. Mmdmum
compaction occurred at a moisture content just below the lower plastic
limit, and, in some soils, within what was considered to be the optimum
moisture range fOr>plowing. However, Thorp (39), working on a Munjor
silt loan in Kansas, found that maximum compaction occurred at moisture
contents about one-feurth the way between the permanent wilting coef-
ficient and.field capacity.

Traffic over dry soils at the Tillage Laboratory had little, if
any, effect upon soil.bulk density unless the soil was very loose (as
after’plowing) prior to passing (16). Dry soils in a loose condition
were compacted temporarily, but little permanent damage was done since
the aggregates were not destroyed (15).

The pressure required to bring about a given compaction depends on
the initial compactive state of the soil. SShne (3 3) has shown that
soils with an initial high pore volume are most affected.by traffic.

Jamison, et a1. (16) implied that, under the same conditions, soils with

F‘

the least clay content will be compacted the least. Huberty (11;)
stated that the highest densities produced by cultivation are those in
which there is a wide range of particle sizes.

3311110 (32) has indicated that the pressure distribution in soil
under rubber tires is dependent upon (excluding soil factors): the
applied load, the tire size, construction, design, and inflation; and
the time during which the tire is in contact with the soil. Forces
applied over a longer time interval produced more compaction, especially
at higher moisture contents. The surface stress under a smooth tire on
a hard, dry soil surface was from 10 to 30 percent higher than the tire
pressure, varying with the rigidity of tire construction; it may be much
less than the tire pressure if the soil is moist because more of the
tire will be in contact with the soil.

Tires with Open centers, according to SShne (32) , produced less
surface pressure than tires of the same size with closed center ribs,
because the radius of curvature of the lugs of the former was less.
he average stress under the rib or tread of a tire was about four or
five times greater than the average surface stress. The "lug effect,"
however, dissipated rather rapidly with depth and was lost within about
three inches on hard surfaces. (m soils of friable consistency the
pressure under the ribs was not very much higher than between them.
Vanden Bets (’42) , however, found that the lugs appeared to carry the
majority of the load even in loose soil.

The pressure at a point in soil is determined both by the applied

unit pressure and the contact area of the applied pressure. Thus when

contact area is reduced, as with smaller tires, or when soil is hard and
lugs only are in contact, soil pressures are reduced. Vanden Berg (h2)
found this relationship to hold in comparing pressures under tractor
wheels with pressures under a sheepsfoot roller. Sohne (33) has reported
that larger tires with more surface contact produced more stress in soil
than smaller tires inflated to the same pressure. With increasing in-
ternal pressure in tires, soil pressure also increased. The front wheels
of a tractor carried between 33 Percent and to percent of the total weight.
Although the weight was less and the tires were smaller, the tire pressure
was greater, and the resultant surface pressure was about the same as
under the rear wheel. Doneen and Henderson (10) found that the dual
front wheels of a tricycle-type tractor caused the same amount of com»
paction (as measured by infiltration) as did the rear wheels.

A comparison of tractor types at the Tillage Laboratory showed that
wheel tractors compacted soils to a greater bulk density and to greater
depths than did tractors equipped with tracks (15), (25). Tractors
equipped with rubber tires generally caused more compaction than when
equipped with steel lugs - up to 100 percent more on some soils. But
200 passes of a two-ton crawler tractor on a moist Ramona loam compacted
the soil to a depth of at least 22 inches (22).

Compaction studies by highway engineers (hl) have shown that if the
bulk density of a soil is plotted against the logarithm of the number of
passes a straight line will result. Thus, the first pass is usually most
effective in compacting a soil. weaver and Jamison (h7), and McClean

and Williams (18) also show this to be the case. Philippe (23) found

that for soil stabilization purposes adequate densities could be achieved
with four passes.

It is no wonder that some soils have compacted "traffic pans"
when it has been calculated, for example, that every part of the soil
in a potato field may be covered by a tire (11) six times during a single
season. weaver (h6) states that in cotton farming "a rear wheel could
conceivably-pass over a given location twenty times per year from plowing
to harvesting, using tractors for all operations."

The work of Jamison, et a1. (16) indicated that maximum compaction
of soils occurred directly beneath the center of the wheel track. Reed
and Berry (26) observed the same under a crawler track. Using smooth
automobile type tires, S3hne (32) calculated that the surface pressure
would be uniform on a hard surface except at the edges when there would
be an increase in pressure of about 25 percent.

Baver (3), reporting the work of Trouse, indicated that under proper
moisture conditions disking a soil derived from a volcanic ash produced
a "barrow sole" or compact layer at a depth of four to eleven inches.
Under rather exaggerated conditions, Parker and Jenny (22) showed that
continued (50 trips over the same area) disking of a dry soil had marked
effects on water infiltration. The intake of the disked plots was re—
duced to about one-third that of the check plots. The bulk density of
the soil was likewise changed to a depth of seven inches by disking the
soil in both a wet and dry state. Except for these references, no other
work has been encountered wherein the effect of a tillage operation alone

on soil compaction is measured. The combined effect of traffic and several

-10..

tallage operations has been reported by Free (11), Struchtemeyer (36),
Blake (6), and others. Many studies on soil compaction have considered
the tractor alone since it is the vehicle that is generally most respon-
sible for traffic. However, the traffic from wagons (32) and other
vehicles may cause even greater soil compaction.

The effect of traffic and tillage pressures on soil compaction have
been measured by many investigators using some type of penetrometer (27),
(28), (35), (38). Bulk density measurements have also been used (16),
(bk). Doneen and Henderson (10) found that bulk density measurements
were not a sensitive criterion for measuring soil compaction, and sug-
gested the use of infiltration measurements.

In many soils pressures are not exerted in a horizontal direction
more than a few inches beyond the tire track (7), (16). The distance
will depend on such things as wheel load, tire width, and soil moisture
content, but it has been reported as small in comparison with the vertical
distribution (31), (37) . Reed (25) indicated, however, that compaction
as determined by resistance to probing was increased from three inches
to seven inches outside the track, and from eight inches to twelve inches
below the track, the distance depending upon the soil and the type of
wheel. vanden Berg (h2) measured small pressures beyond the edge of the
tire to distances equal to 50 percent of the tire width.

The depths to which soils are reported to have been compacted by
traffic vary widely} Reports from almost none under already dense dry
soil to a measurable quantity 2h inches below the surface have been
made (22). Evidence of traffic induced compaction 12 to 15 inches below
the surface has been reported frequently (19), (20), (36).

g

Little is known of the magnitude of the forces causing the compac-
tion mentioned above, nor how and under what conditions they are trans-
mitted through the soil. Thorp (39) has estimated that a pressure of
200 pounds per square inch is exerted by a rear wheel of a tractor under
load. S3hne (32) reports a. maximum pressure of 30 pounds per square inch
under a rear tractor tire inflated to 12 pounds per square inch and under
a 1200 pound load.

It is not the purpose of this review to consider the effect of
compact soil conditions upon the production of agronomic crops. For a
consideration of the application of the basic compaction data, the
reader is referred to the excellent reviews in Chapters 1 and 2 of

Soil Physical Conditions and Plant Growth (1), (l7).

 

INSTRUMENTATION

Cell Design

The electrical strain gage (9) is one of the tools which has been
used for sometime by the engineer interested in measuring stresses in
materials. A strain gage is a grid of very small diameter wire bonded
to a surface so that the wire is strained in the same amount as the
outer fibers of the specimen. The resulting deformation of the wire
produces a proportional change in resistance which can be measured
electrically.

To measure the pressures in undisturbed soil a load cell utilizing
strain gages was desigIed by Prof. P. DeKoning of the Applied Mechanics
Department of Michigan State University. For design and a view of the
completed cells see Figures I and II on pages 13 and 11;. When pressure
was applied to the piston the inner thin—walled member was stressed.

The strain was measured electrically by 8. Brush recorder.

Four electrical strain gages (SR-h type) were placed equidistantly
around the cylinder to be stressed. This was done to average the stretch-
ing of the cylinder walls, since there is always some bending in a cylin-
der no matter how carefully it is loaded. Opposite "active" gages were
wired in parallel. A "dmmny" gage was bonded to an unstressed plate
mounted on the base of the cell. This gage served to compensate for tem-
perature effects so that resistance changes in the active gages were

always due to stress changes.

-12..

    
  
 

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SOIL TEST
LOAD CELL
PISTON AREA=2.5$q.in.

 

 

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Figure I - Scale drawing of load test cell.
The thin-walled stressed tube is designated by the

nal

letter A. (Photographically reduced to 23/32 origi-
and.

 

Figure II - Photograph of soil load test cell. Left - assembled
cell complete with electrical connections and ready for placement in the
soil. Right - disassembled cell showing strain gage mounted on thin-
walled stressed tubing.

-15..

To be completely satisfactory for use in soils, a load cell should
be so constructed that it compresses, defame, and, in general, behaves
just like soil material when pressure is applied to it. The possibility
of encountering a material which could be so tooled is rather remote.

It was proposed to measure the pressure in undisturbed soils. The soil
deformation under such conditions would normally be less than where
loose or disturbed soils were to be used. A cell with a broad base
would not yield greatly to surface pressures since the unit pressure
exerted by the base on the soil beneath would be very low compared to
the unit pressure registered by the cell. Hence the cell would not tend
to sink into the soil but would register the load imposed upon its head.

Using this type of cell under conditions where the soil is loose
would certainly result in recorded pressures higher than those in an
undisturbed soil because of arch action. That such does happen has been
observed by Cooper (8).

To measure soil behavior at a "point" the cell piston was made as
small as possible. A diameter of 1.59 inches was chosen to give an area
of 2.5 square inches and thus give a simple conversion factor of 0.11 for
use in computing the soil stress, 8. Thus, 8- (0.1;) P, P being the

recorded load registered by the cell.

Cell Construction
The cells were fabricated of stainless steel to avoid rusting and
to permit use under moist soil conditions. In the original desim the
walls of the tube to be stressed were too thick to give sufficient

sensitivity in the pressure range needed. A wall thickness of 0.01:2

- 16 -

inches was feund.to be satisfactory. Considerable technical difficulty
was encountered in soldering this thin-walled member to the thicker
pieces at each end. Several of the silver solder joints broke at the
time of calibration and all the sleeves had to be re-machined because
the thinswalled tubing was not assembled perfectly horizontal. On the
repeat solderings, low temperature solder was used and the connections
were sweated together. This seemed to form a joint strong enough to
withstand the pressures involved.

Cementing the strain gages on the tubing proved to be quite a task.
If tape was used to supply enough pressure to assure a good gage to metal
bond, the gages invariably shifted in position as the tape was applied.
If no tape was applied, the edges of the flat gages would.not adhere to
the cylinder. A wooden die held.in position by C-clamps was found to
be the answer to this problem.

The exterior electrical connections were housed under the base of
the cell. The junction box was insulated from.moisture by filling it
with wax. Molten wax was also introduced into the cell interior through
a port to waterproof the internal electrical connections.

In spite of the above precautions, shorts often developed and
resistance-to-ground was reduced to the extent that sensitivity was lost.
In the first installation the cells remained underground for about three
weeks awaiting drier soil conditions. At the end of that time one-half
of the cells were inoperative. Drying to 100° C. in an oven failed to
correct the condition and the cells had to be completely disassembled
and new gages installed. In a subsequent installation the cells were.

placed in vinyl plastic bags in an attempt to provide a vapor barrier.

 

-17..

This procedure was unsatisfactory'because the bags were torn as the
cells were placed.into position. ‘When short circuits developed over-
night in gages buried in a wet soil, it was decided to run all further

tests the same day that the cells were buried.

Cell Calibration

After waterproofing and checking for correct electrical wiring,
each cell was calibrated. 'Weights were placed on top of a cell and.the
number of lines of deflection on a Brush recorder was noted. ‘Using an
attenuation factor of 10, each line on the Brush chart represented a
strain of 10 microinches. In addition to the dead weight loading, static
loads were applied.hydraulically using a Tinius-Olsen load.machine.
Deflection under this loading usually was reduced, especially at pres-
sures less than 100 pounds per square inch.

The sensitivity of each cell was checked periodically. From the
calibration data Obtained, a curve (load in pounds vs. strain in micro-
inches) was prepared. Figure III is an example of such a curve. The
cell calibration curves used in l95h were Obtained with the use of the
Tinius-Olsen apparatus. In 1955 calibration curves using both dead
weight and.machine loading data were prepared, but only the former were

used.

LOAD IN POUNDS

450

400

350

300

N
0'
O

N
O
O

G
o

5
0

0|
0

 

-18-

CELL NO. IOS

50 I00 I o
STRAIN IN MICROINCHES

Figure III - Sample of a calibration curve

-19..

Pressure Recording

The strain produced in a buried cell by loading the surface of the
soil was recorded in most instances using a 12 channel Hathaway recorder
generously provided by the Michigan State Highway Department (see Figure
IV) . The Operating principle of this instrument is similar to the Brush
recorder, but has an advantage in that strain in 12 gages can be recorded
simultaneously. The Hathaway instrument was calibrated so that a strain
of 200 microinches gave a deflection of 30 mm. on the trace. With this
calibration each m. of deflection represented about six pounds per square
inch. The pressure varied of course with each cell. Figure V is a
sample of 'a trace made by the Hathaway instrument.

To calculate the pressure, the deflection produced by each pass of
the equipment was first measured in mm. The equivalent strain was then
calculated from the above relationship using simple proportions. The
total pressure recorded was finally obtained from the cell calibration
curve. For pressure in pounds per square inch the total load was divided

by 2.5, the contact area of the cells.

 

b
c

O

U

 

Figure IV - Scenes during installation and operation
of soil pressure measuring equipment

View of excavation showing test cells being placed at various depths
under undisturbed soil. String, indicating 0 position, crosses
upper right of photo.

Truck housing Hathaway equipment. Cell-recorder connections are
visible in the foreground.

Hathaway recorder mounted in Michigan State Highway Department truck.

Action view of combine passing over test area (Spinks sandy loam).

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PROCEDURE

Cell Installation

Except when tillage implements were used, the investigations were
made on.undisturbed soil in situ. The undisturbed site was prepared
in the following manner. A pit three feet by six feet'oy two feet was
dug. On one face of the pit the soil was removed at several locations,
each location at a different depth from.the surface. The soil was re-
moved.in such a fashion that an opening, the same size and shape as the
load.cell, was made. The excavation was continued.under the undisturbed
soil.until the center of the top of the cell was three inches from.the
face of the pit. The entire cell was then pushed in.beyond the pit face
at least one-quarter of an inch and good contact with the soil above was
secured‘by driving wedges under the base of the load cell. Figure IV (A)
shows the pit and the cells being installed. Care was taken not to pre-
load the cells, although any such loading could be compensated for in
"zeroing in“ the recording instrument.

Befbre backfilling the excavation the number and.position, both
horizontal and vertical, of each cell was recorded. The position was
reckoned with respect to a zero line. The altitude of this line was
the mean ground.level and its position coincided with the surface edge
of the excavation. Passes (runs) were made with the various vehicles
at various positions with respect to the zero line. In describing the
position a code symbol was used to give both the direction and the dis-

tance from the outside of the rear tire to the zero line. For instance,

- 22 -

-23..

the position N3 indicates that the outside of the tire followed a path
which was three inches north of the zero or reference line.

In backfilling the excavation an attempt was made to return the
excavated soil to its original horizon and density. At some locations

a cell was placed in this disturbed soil.

Soils
The soils for the pressure measuring part of the study were selected

to give a range of textures. A Plainfield sand at the Rose Lake Wild-
life Experiment Station (Clinton County) provided the coarse textured
soil. The Ferden Farm in Saginaw County provided the site for the fine
textured soil, vim, Sims sandy clay loam. Hillsdale sandy loam and
Spinks sancv loam, both located at the Michigan Experiment Station Farm,
served as test areas for soils of intermediate texture. On each of the

last three named soils, tests were made at two moisture levels.

Equipment

Table 1 contains a list of the equipment used at each site to-
gether with other pertinent data. The vehicles were operated at a speed
of about one mile per hour, except for one test when for one replicate
a tractor was operated at six miles per hour. The vehicles were not
loaded in any manner 3 they merely were driven over the test area.

Considerable variation in pressure was recorded from consecutive
runs at the same site. This variation occurred mostly at shallow depths
with a tractor rear wheel. It was thought that the lugs on the tire
might be responsible for this variation. To investigate this further,

a small hole was dug five inches deep. A load cell was placed in the

-2h-

TABLE].

PI'RTINEN T DATA OF EQUIPMENT USED IN LOAD
TEST STUDIES ON SEVERAL SOILS

 

 

 

Rear Tire Approx.
Soil Equipment Tire Size Pressure Wt.
Sims sandy Ferguson tractor 11 x 28 12 3500
clay loam
Ford 1-ton truck 7.50 x 15 145 1500
Massey-Harris combine 8 x 2h 12 5300
Plow - - 350
Plainfield Ferguson tractor 11 x 28 12 3500
sand
Ford 1-ton truck 7.50 x 15 145 1:500
Ford tractor with - - 3800
rubber half-track
Plow - - 350
Hillsdale Ferguson tractor 11 x 28 12 3500
sandy
loam Caterpiller D-h l7 - 12000
Ford l-ton truck 7.50 x 15 J45 1500
Ford car 6.70 x 15 25 2900
Case tractor 10 x 38 12 1000
Allis-Chalmers tractor 9 x 2h 12 2100
Plow - - 350
Disk - - 1400
Spring-tooth harrow - - 200
Spinks Ferguson tractor 11 x 28 12 3500
sandy
loam Caterpillar D-h 17 .. 12000
Massey-Harris combine 8 x 2h 12 5300
Ford truck 6. 50 x 15 115 1:500

Plow - F- 350

-25..

center and the hole covered with an iron plate three-eighths of an inch
thick in which was cut an aperture slightly larger than the diameter of
the top of the cell. On top of the plate and over the cell was placed
a piece of carbon paper between two sheets of paper. As the tractor
tire moved over the cell the position of the lug with respect to the
cell was traced. Thus, it was possible to record the pressure and tell

how much and what part of the lug actually was in contact with the cell.

Vehicle 00mpaction

The compaction produced by traffic was determined by measuring soil
bulk density. The tires of the vehicle were run in the same track 25
times. Ten soil cores (to), three inches by three inches, were taken
at each of several depths after the first, fifth, and twenty-fifth pass.
Samples were taken at zero to three inches and four to seven inches on
each occasion and also at the eleven to fourteen inch depth after the
twenty-fifth pass. In addition, 20 cores were taken from adjacent un-
disturbed soil at zero to three inches,and ten cores each from the four
to seven and eleven to fourteen inch depths. The soil bulk density was
calculated from these cores using standard procedures. A series of
cores (110 in all) was obtained at several locations and under varying
moisture and surface conditions. The soils compacted, together with
some of their physical properties are listed in Table 2.

The uncompacted, untreated cores were compacted artificially in the
laboratory. Soils already compacted by one or more tractor passes were
less responsive to loading in the laboratory and their use was discon-
tinued. Compaction was effected by means of the instrument shown in

Figure VI (30). The compacting plunger was 2.95 inches in diameter. It

- 26 -

TABLE 2

SOME PHYSICAL PROPERTIES OF SOILS
COMPACTED BY TRAFFIC

 

 

Upper Lower

Site 5 z % Plastic Plastic
No. Sand Silt Clay Soil Type Limit Limit
1a 69 23 8 Berrien sandy loam 26.7 18.9
b h8 39 13 19.8 1h.0
2 h? hh 9 Conover 10am 35.3 23.2
75 17 8 19.3 1h.3
3 77 1h 9 Hodunk sandy loam 17.h 1h.6
7o 22 8 13.6 11.2
h 72 20 8 Hillsdale sandy loam 19.3 1h.9
72 20 8 16.8 13.1
5 60 20 20 Sims sandy clay loam h1.5 25.3
67 16 17 30.5 16.h
6 ts 32 25 Brookston loam 38.7 23.5
57 20 23 29.0 16.6
7 73 18 9 Spinks sandy loam 19.5 15.3
75 16 9 1h.6 13.1
8 - - - Conover 10am - -

 

a Surface soil - 0-8 inches
b Subsoil - 10-15 inches

-27-

 

 

 

Figure VI - Instrument used to compact soil cores in the laboratory.
Amount of compaction is being measured in the core at the left.

was placed on the surface of the soil and the piston was lowered with
a predetermined pressure controlled by a pressure regulator.

From the load cell tests it was determined that the cells in the
field were loaded between three-fourths and one second. The pressure on
the soil cores was released after a corresponding time and the new depth
of the soil measured. Pressure was applied to the soils repeatedly and
the new soil depth measured after one, five, and twenty-five compactions.
From these measurements new volumes and, hence, bulk densities could be
calculated.

Reeves and Nichols (21;) working with confined soils found that
arch action was great enough, even at low pressures, for friction on the
cylinder wall to absorb some force. At locations four and five (see
Table 2) some of the soil cores were taken in cylinders which had been
well greased on the inside. With the lubricant present, the bulk den-
sity under a given pressure was increased slightly. The lubrication

was not continued, however, since the differences were not great.

RESULTS AND DISCUSSION

Magnitude of Soil Pressure

The primary objective of this study was to ascertain the magnitude
of loads being applied to soils daily by American farmers. It was
realized at the outset that certain factors, viz. soil texture, soil
moisture, and type of farm machine would probably affect the pressure.
Thus these variables were included in the original experimental program.

Incidental to an investigation of the main objectives of this sec-
tion was the measurement of the effect which vehicle speed and tire
lugs had on the pressures in the soil. Some data were also obtained
on the existence of horizontal and negative pressures and on the pres-
sure effect of a loaded vs. empty truck.

The load cells were machined and assembled early enough in l95h
to permit testing on the Plainfield, Hillsdale, and Sims soils. A
sample of the data which were recorded photographically is presented
in Figure V. The maximum displacement of the peaks was measured to
two-tenths of a millimeter. With a knowledge of the recording instru-
ment and cell calibrations the pressures could be calculated in pounds
per square inch.

The pressure cells theoretically were sensitive to one pound per
square inch. Due to the vagaries of instrumentation and vehicle opera-
tion, it was considered more realistic, however, to express the pres-

sures in multiples of five pounds per square inch.

- 29 -

In Table 3 the maximum and average pressures recorded at the various
depths in the different soils are presented. The average pressure exp
presses the results from at least three runs, although the data from.all
runs were used where the pressure was of a magnitude similar to the maxi-
mum. If the three highest recorded.values were quite dissimilar no
average is given. The maximum.pressure thus represents the pressure that
may'be expected in a small area under the wheel. The average pressures
can.be expected to occur over a greater area. ‘At the deeper depths the
maximum.and.average pressures recorded were similar. Near the surface
a greater difference existed between the average and maximum.pressures.
The difference between the two values is an indication of the variability
between the maximum and other high pressure readings.

Several statements with reference to the data in Table 3 may be
made. Pressure, in general, decreased.with depth. There were occasions,
however, when the pressure recorded at a particular depth was greater
than that recorded at a shallower depth. This situation was contrary
to expectation (30) and.was explained originally as being caused.by'im~
proper cell placement or calibration. Gill and.Reaves (13) however,
have reported recently that they measured pressures at a nine-inch depth
in soil which exceeded the pressures at a five-inch depth by more than
50 percent. From the data at hand it is impossible to state whether
these anomalOus values represent real pressures or whether they are due
to faulty technique.

The largest pressure decrease was in the surface few inches. No
pressures were measured below about 16 inches. The theoretical consid-

erations of S3hne (3h) predicted these results.

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-31..

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- 32-

Vehicle effect. Pressures under the rear tractor wheels tended
to be slightly greater than under the front wheels. The contact area
and wheel load of the front wheels were smaller. The internal tire
pressure was greater. The net result was that soil pressure under the
front wheel was somewhat less than under the rear wheel. Sohne (32)
reported that soil pressures increased with increasing internal tire
pressure, load, and contact area, if the weight per unit area remained
unchanged.

‘A comparison of the pressure at various depths under the front
and rear wheel of the tractor revealed that pressure under the rear
wheel extended deeper. This is due to the greater rear wheel load and
tire width.

Peaks were consistently slightly higher (greater pressure) under
front track tires than under rear tires. Front and rear tires were the
same size and were inflated to the same pressure. With an empty truck
more than 50 percent of the load is on the front wheels, and the data
bear this out.

In these tests surface pressures under the wheel of an empty one—
ton pickup truck were approximately twice those under the rear wheel
of a mediumpsized tractor. The pressure difference lessened with depth,
but was recordable to a depth of about 10 inches.

Unusually high pressures were recorded at the one-half inch depth
under the Ford hslfatruck on the Plainfield soil. Some of the increase
under the front tires may be attributed to the additional weight of the
added tracks. The large pressures under the rear wheel are probably due

to the fact that the rear tire is made more rigid by the tracks and as

-33..

a result more weight is supported by the cell, which is also rigid,
than by the surrounding soil.

Pressures under the Ford were smaller than under the Ferguson at
depths greater than three inches. The surface pressure was undoubtedly
decreased due to the increased contact area effected by the tracks.

It is to be further noted that the recorded pressures under the
small Mia-Chalmers tractor were also high. Even the small light-
weight tractors may be quite effective in causing soil compaction, be-
cause with smaller tires the unit surface pressure remains high.

During 1955 the test cells were placed in three soils. Additional
equipment available for testing included a D-h Caterpiller tractor and
a Massey-Harris Clipper combine. The data obtained are included in
Table 1;. Pressure distribution, magnitude, and variability were very
similar to those found during the previous year.

Pressures recorded under the combine were of the same order of
magiitude as those recorded under the pickup truck. Variable results
were obtained with the Caterpillar, but with both soils tested, pres-
sures under the treads were as great, if not slightly greater than
under rubber tires. This was especially true at the deeper depths.
Undoubtedly the bulb of pressure (37) under the Caterpillar extends to
great depths due to the large track cross-section. Although the vehicle
weight divided by the track contact area indicates surface pressures of
less than seven pounds per square inch, the vibration produced by a
crawler tractor may contribute significantly to compaction (S) .

Negative pressures were recorded consistently under the tractor

front wheel on the Spinks soil regardless of the position of the tire

- 3L -

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-35-

with respect to the gage. Negative pressures were recorded on occasion
with all vehicles at various depths in each soil and were generally asso-
ciated with tire position. When the outside of the tire passed to the
side of a gage the trace peaks reversed direction. It is possible that
a suction is created at the edge of a tire in its motion over the soil
which would result in an unloading of the cell.

On some traces, those in Figure VII for example, both positive
and negative pressures were recorded. In most cases the negative pres-
sure preceded the positive, and was not of very great magnitude.
vanden Berg (h2), using an entirely different type of pressure cell,
also observed small negative pressures in soil. It must be admitted
that at the moment neither the significance nor the effect of negative
pressures is definitely known.

An examination of the records after the initial series of passes
revealed that there was considerable variation between peak heights on
consecutive runs. The only difference between runs was a slight change
in the position of the vehicle with respect to the cell. A “lug effect"
was suspected and at the next site (Sims clay loam) duplicate passes
were made at each position. Table 5 summarizes the variability in
recorded pressures at several depths under a Ferguson tractor rear wheel.
As was suspected, the greatest variability and effect of the lugs was
nearest the surface. This effect is of special significance in measur-
ing pressures under an undisturbed soil where the soil is apt to be firm
and where only the lugs contact the surface. This variability in recordp
ed pressures with consecutive passes, coupled with the variability intro-

duced by inability on the part of the operator of the vehicle to follow

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<

 

- 37 -

the intended.line precisely, supply good.reasons for the use of maxhnwm

pressures as used in this report.

TABLE 5

VARIABILITI IN RECORDED ERESSURES FROM TWO PASSES WITH FERGUSON
TRACTOR REAR TIRE.AT VARXING DISTANCES FROM CELL

 

 

 

 

Number of Average Difference Deviation in
Duplicate Average in Pressure Between Average
Depth Passes Pressure Duplicate Passes Pressure
Inches Pounds_per square inch, Percent
o 9 6h 50 78
3 12 b6 22 he
7 1h 18 h 22
12 13 18 h 22

 

In addition to showing that lugs in general affected recorded
pressures, it was further established that the pressures recorded in
the surface soils were greatly'influenced.by the position of the lug
relative to that of the gage.

Using the technique described.under Procedure, the data for the
curve in.Figure VIII were obtained. A statistical analysis of these
data revealed that the regression coefficient was significant at the
one percent level. There was no relationship statistically between
the recorded.pressure and the portion (i.e. inside, center, outside)
of the lug in contact with the test cell.

0n the Hillsdale soil several runs were made with the tractor at

increased speeds. From the results as shown in Table 6, it may'be

INCHES

AREA - SQUARE

 

-38..

 

 

    
  

 

AREA or FULL CONTACT
150'
EQUATION or Recasssnon LINE

v=lzasx + 552
L20-
.80-
.40-

A A A L A A .

40 so I20 I60 200 240 230

PRESSURE — POUNDS PER SQUARE INCH

Figure VIII - Relation between recorded pressure and

the position of the test cell with respect to the tire tread.

-39..

concluded that increasing the vehicle speed resulted in a slight increase
in the pressures near the soil surface. Although the pressure increase
with speed was not great, it is believed to be real because of the con-

sistency of the results.

TABLE6

EFFECT OF VEHICLE SPEED ON AVERAGE SOIL PRESSURE-S
IN HELSDALE SANDY LOAM

 

 

 

 

 

 

Speed . 1 ugh 6 mph
Depth Wheel Front Rear Front Rear
Pressure in pounds per square inch
2" 15 15 25 20
7" S S S 5
12" 5 10 5 10

It has been pointed out earlier that the recorded pressures under
the front wheels of an empty one-ton pickup truck were greater than
under the rear wheels. To ascertain the pressure relationships under
loaded conditions, a one-ton load was placed in the truck. The pres-
sures recorded before and after loading are given in Table 7. The test
was carried out on a Spinks sandy loam.

The contact area of a tire on a hard surface is generally assumed
to be in the shape of an ellipse (31;), (142). The soil in the test area
was firm and sodded, but the contact area was undoubtedly increased on
the average 10 or 15 percent due to loading and some simdng into the
soil. Using the latter figure, the contact area would have been 31

square inches.

- ho -

The load was added to the extreme rear of the truck with the result
that some of the weight was shifted from the front end. The net load
increase on the rear then was equal to 35 Pounds per square inch
[170-120- (160-1115) Psi] . This pressure multiplied by the contact area
gives 1085 pounds load per wheel or 2170 pounds total. This value

compares favorably with the weight of the load added.

TABLE?

PBESSURES AT VARIOUS DEPTHS UNDER AN EMPTY AND
LOADED FORD ONE-TON PICKUP TRUCK

 

 

 

 

 

 

 

Truck mi ‘ Loaded
Pres sure Maximum Average Msxinmm Average
Tire Front Rear Front Rear Front Rear Front Rear
.RSEEE
In.
1} 160 120 130 110 1h5 170 120 1&5
3% 6 5 60 60 SS 60 85 50 80
h} 145 ho us 30 3o 65 25 55
10% 20 1s 1s 15 1s 35 1s 30
17 S 5 5 S 5 15 5 15

Another statistic from the manufacturer shows that about seven
hundred pounds more weight is carried by the front wheels than by the
rear wheels of an emoty ton pickup truck. This means an additional
12 pounds per square inch surface pressure in excess of the rear wheels.
The average pressure advantage (using madman pressures to a depth of
three inches) in favor of the front wheel on all tests where the pickup

was used was 12 pounds per square inch.

The close agreement between recorded and expected pressures indicates
it is believed, that the pressure cells may be used to measure soil pres-
sures cpantitatively within the zone of their sensitivity. A small piece
of evidence which strengthens faith in the accuracy of the test cells
may be cited further. At the close of one of the test runs, several of
the personnel present stood over the cell nearest the surface. It was
calculated that the pressure applied at the surface was about 11 pounds
per square inch. The pressure recorded by the cell at a depth of two
and one—quarter inches was ten pounds per square inch.

soil effects; The period in which the data were taken in 1955 was

 

dry. Water was hauled to the test areas, but in spite of the "irrigation"
the extremes desired in moisture content were not realized. The data
obtained under the "wet" and "dry" conditions are shown in Table 8.

Based on the comparisons available it is evident that pres sures increased
with increasing moisture content except on the Sims soil. In fine tex-
tured soils with increasing moisture content surface pressures are re-
duced due to pester tire contact area caused by the wheel sinking deeply
into the soil.

At two locations cells were placed under undisturbed and disturbed
(tamped backfill in the pit excavation) soil. The pressures recorded
are given in Table 9. The data support the observations made by Vanden
Bert (142) who noted that the pressure in a loose soil was greater than
that in the same soil at a higher bulk density.

If it is true, as is suggested by the data in Table 9, that soils
with low bulk density transmit pressure more readily than soils. with high

bulk density, then the pressure in coarse textured soil should be low

- h2 -

TABLE 8
MAXIMUM RESURES IN SOME SOIIS AT DIFFERENT MOISTURE CONTENTS

 

 

Massey-Harris

 

 

 

 

 

_V_ehicle “Ferguson Tractor Combine
Whe el Front Rear Drive
Broil Moisture 'Dry" " '11? 1? t' _Dry__Mo_i's_t _Dry: ’ ‘ Moist
Depth
In.
inks can loam. 1% (~) 60 15 70 55 150
moisture

 

dry .moist 3 1o 25 25 25 75 95
Depth soil soil

 

0-3" 15.5 17.0 5 o 15 2o 35 80 90
3.6- 13.6 16.0
6.9" 13.3 16.0 6% o 10 1o 15 70 to
9-18" 11.5 12.2
10 o 5 o 15 1o ho
-h-_-9-_9___i_$%_-w.-% ......
fiéya_gsg§z;g%§%fi%%§2 1% 60 ho 60 50

 

i t
W 2:21 “1:018; 3 30 35 30 25

0'9" 20.9 21.3
9418" 27.0 28.6 5 35 25 65 20

 

 

 

 

 

 

7 5 10 3o 20
10 5 10 15 10
15 O 10 O
Hilledale can loam _- Chevrolet Pickup
X moisture Front Wheel Rear Wheel
dry moist; Dry Moist Dry Moist
Death 8°11 8°11 2 us 20 55 120 115 120 110 120

 

0-2" 12 .0 «-

he?" 1h.5 - 7 10 o 10 25 25 25 25 25
1o-12n 16.0 -

8 - o - ho - 20 - 20

12 10 - 10 - 15 - 15 -

 

‘ No moisture determinations made. Test made 3 weeks previous to
companion. In interim rain kept off of sodded area.

- h3 -

because of its normal high bulk density. This did not always appear to
be the case.
TABLE 9
MAXIMUM SOIL PRESSURES IN DISTURBED AND UNDISTURBED SOILS

 

 

—_—

 

 

 

Depth rDisturbed Undisturbed
Inches Vehicle Soil Front Rear Front Real;

 

Pres sure in pounds per square inch

6a Ferguson Hillsdale 3o 25 1o 10
tractor sancbr loam

7 Ford tractor 5 25 10 25

3 Ferguson Sims clay loam 35 65 20 11,0
tractor

6a 10 2o 10 15

3 Chevrolet ton Sims clay loam 125 110 85 75

pickup truck
63 35 no 20 20

 

‘ Seven-inch depth in undisturbed soil

Unfortunately data were not obtained at the same depths in each
soil, so direct comparisons are not always possible. From the data in
Tables 3 and h it appears, however, that in most cases the pressure in-
creased with the coarseness of soil texture. Since coarse textured soils
generally have high bulk densities, this means that pressure increased
with increasing bulk density.

Perhaps the contrasting results are not incongruous. Pressure dis-
tribution in soils may be associated with pore size and particle contact
areas. The mean pore size is probably greater and the contact area less

in a disturbed soil than in an undisturbed soil. If soil pressure increases

- hh -
with increasing mean pore size and decreasing contact area, then higher
pressures should be observed in the disturbed soils. Such was the case.
In general, the mean pore size of soils increases and the contact area
‘ decreases with an increase in sand content. Sandy soils then would be
expected to transmit the applied pressure to a greater extent than soils

with finer particles predominating. Again such appeared to be the case.

With the limited data available, it is impossible, of course, to
state with certainty that either the explanation or the data represent
the actual condition. Additional information will be needed to elucidate
this subject.

Residual stresses in the soil were not observed generally. There
were occasions, however, when the trace did not return to its original
‘ position when the cell was unloaded. See Figure VII. When this oc-
curred, the peak displacement was measured from the newly established
base line. Bernhard (5) also observed a small amount of retained pres-

‘ sure in his work on static and dynamic soil compaction.

Tillage implement effect. Only one cell installation was made
expressly to ascertain soil pressure under tillage implements. At other
sites, however, after the last vehicle pass, the shallow gages were re-
moved, and the area over the deeper gages was then plowed. The results
of these tests are shown in Table 10.

The "plow" position referred to in the table refers to that pass
in which the plow point came most closely to the gage. Plowing was
started at a set distance from the gages so that the point of the rear
plow would pass over the gage at the "plow" position. The tractor wheels

then, following the furrow, would pass over the gages on the "after plow"

-15-

TABLE 10

W ASSOCIATED WITH PASSAGE OF TILLAGE DIPIEMENTS

 

 

7" Depth 10" Depth 15" Depth
Wheel Wheel Wheel
Soil Implement Position Front Rear Front Rear Front Rear

 

 

 

 

 

Pressure in pounds per scpare inch

Plain- Plow Preplow 0 (-) 0 1o 0 0
f 1016. Plow O O O O O 0
send After plow (-) 0 30 25 0 0

Plain- Plow Preplow 5 20 (~) (-) - ..
field Plow O 0 O O - «-
send After plow 25 30 20 (-) - «-

Hills- Plow Preplow O O 0 O - -
dale Plow O 5 O 0 - -
m Mar plow 0 (-) O (D) c- as
loan

Disc Various 0 5 O 10 - «-
Spring- Various 0 5 O 5 - -
tooth

Sins Plow Preplow 0 (-) O (-) O (-)
sandy Plow o o o (-) 0 (-)
clay
loam Plow Preplow O 10 5 15 - -

Plow - - 0 15 O 0
After plow - - O 20 O 10

Bpinks Plow Preplow O (-) O (-) O 20
sandy Plow - - O O O 0
loan A’fter plow - - O (-) O O

Plow Preplow - - O 10 O 5
Plow - - O O O 0
After plow - - 10 10 5 10

-lL6..

pass. Plowing was done to a depth of seven inches. The disking and
harrowing took place just subsequent to plowing the sod on the Hillsdale
soil.

In the majority of cases no pressure was recorded on the "plow"
pass. Negative pressures were recorded on some of the "preplow" and
'after plow" passes. On the traces obtained during the tillage trials
there was no way of deciding whether the pressure was associated with the
plow or the tractor. Since no pressure was recorded when the plow was

closest to the gage, the pressures recorded on the other passes are

 

probably due to the tractor or implement wheels and not the implement

 

itself. It would seem from these data that the so-called "plow pans"
are not caused by the plow or tillage implement per se, but by the wheels

of the vehicle which draws it.

Pressure Distribution

At the initiation of this investigation it was planned to study the
distribution as well as the magnitude of the pressure in soils. From the
data presented earlier in Tables 3 and h a quantitative estimate of the
distribution vertically can be obtained. No information is available
there concerning the horizontal distribution, however. The variability
in successive pressure values (discussed on page 35) made it extremely
difficult to obtain smooth and symmetrical isobars when plotting pres-
sure in two dimensions. Two sample plots are presented in Figures IX
and X. To obtain the isobars the pressures recorded at one depth were
plotted against the position of the tire with respect to the gage. A
smooth curve was drawn from these points. The curves at each depth were

then combined.

DEPTH ' INCHES

-
VEHICLE'

 

J W EDGE 0: TIRE,2 4 ? magmas)

      

SOIL'
PLAINFEL ‘
SAND
MOISTURE‘
MOIST (‘57.)

FERGUSON
TRACTOR

IO PSI

ISOBARS UNDER REAR TRACTOR TIRE

Figure IX

 

DEPTH - INCHES

a
1

G
v

SOIL‘ SIIS CLAY
0- LOAD!

-h8-

§ f EDGE 0; TIRE 2 ' 4' g (INCHES)

I50 PSI

    
 
   
   

IOO PSI

 

MOISTUIE‘ DRY
02$)

VEHICLE ' ONE TON
PICKUP

 

'9;

ISOBARS UNDER REAR TRUCK TIRE

Figure X

"h9" I

It can be seen from these figures that there was very little hori-
zontal transfer of pressures in excess of ten pounds per square inch.
Pressures of this magnitude or greater occurred within a distance equal
to the tire width plus four to six inches. The shape of the isobars
probably would change with moisture content as SBhne (3h) has pointed
out. That they lengthened with increasing moisture may be seen by
referring to Table 8. It was not possible to show that the horizontal
distance was decreased.

As will be pointed out in the next section, pressures sufficient
to cause a measurable change in soil bulk density were present under
farm vehicle tires to a depth of twelve or more inches, especially if

the soils were moist. When plowing, one tractor wheel runs in the fur-

 

row. This twelve inches is then in reality eighteen inches or more from
the surface. It is believed that this practice, followed yearly in the
intensively cultivated areas, is the predominate causal agent for the
development of the pan condition so prevalent in these soils. I
At three locations one cell was placed at a 3-inch depth in a
horizontal rather than vertical position. The pressure recorded by these
cells is given in Table 11. The maximum values were obtained when the
tire was so positioned that about one-fourth of it was directly over the
non-sensitive shank portion of the test cell. On the average, the pres-
sures recorded by vertically positioned cells were 2.7 times greater
than the pressure recorded by the cells placed horizontally at the same

depth.

_ 5o -

TABLE 11

MAXIMUM PRESSURE AT A DEPTH OF THREE INCHES AS MEASURED BY
A TEST CELL IN A HORIZONTAL POSITION

 

 

 

 

 

Soil Hillsdale Sims Plainfield
, Sandy Loam Clay Loam Sand
vehicle Wheel Front Rear Front Rear Front Rear
Ferguson psi - us 15 20 10 15
pos.a 9 6%-9% 7-10 7% 5%
Case psi - ho
P050 6’9
Allis-Chalmers psi 0 20
pos. 7
Ford half-track psi 0 70
pos. 8
Fordb psi hS AS 35 35
pos. 8 8 3% 1-2 I

 

‘ Distance in inches

b Pickup

from tire outside to cell.

 

 

-51..

Soil Compaction

Field: As a corollary to the measurement of pressure in soil the
compactive effect of traffic was studied. The tractor was chosen as the
standard because it is the vehicle most frequently used under average
operational conditions. Also, considerable pressure data was obtained
with a tractor. To ascertain the effect of repeated traffic on soil
compaction, soil bulk density measurements were made after one, five,
and twenty-five passes of the tractor in the same track. These data

were obtained only from the center of the track and hence reflect,

 

probably, maximum compactive effect. For a more complete picture of
compaction under a tractor tire the reader is referred to a paper by
Gill and Reeves (13) in which they present bulk density measurements
at various positions both within and outside the wheel track.

It was conceived that once the magnitude of the pressures from
traffic at various depths in soils was known, these pressures could be
applied to undisturbed soil cores taken at corresponding depths and the
susceptibility of a particular soil to compaction could then be deter-
mined. Thus the time-consuming task of taking soil cores before and
after traffic in the field could be reduced to a simple laboratory
dstssndnation on samples which would normally be necessary to measure
the natural bulk density.

The ultimate degree to which a soil will be compacted by traffic
depends both upon the soil and the compacting vehicle. The same tractor,

a Ferguson, was used throughout these tests, except where noted, and

hence no vehicle variables were introduced. The soil variables consid-

ered were moisture and original bulk density.

 

-52-

Soils at four sites were compacted at two moisture levels. Compac-

 

tion data at three other locations were also obtained. These data are
presented on the left hand side of Tables 12 to 18.

Bernhard (5) found that most of the settlement in soils caused by
compaction occurred in the first two vehicle passes. The data show that
the greatest change in bulk density in the surface soil is associated
with the first pass. This is especially true in the case of moist soils.
See Table 19.

With increasing moisture content friction between soil particles
was reduced and the soil became more susceptible to compaction when a
load was applied. This relationship held for all moisture contents
until the soil pores were filled with water. Once the soil was satur-
ated, further increases in pressure did not alter the bulk density.

This may be clearly seen in Tables 13 and 15 where pressure above 50
pounds per square inch failed to change the density of the surface soil.

The pressure increase with increasing moisture, discussed in the
first section of this report, may be another factor contributing to the
effectiveness of a given load in causing compaction under moist soil
conditions.

Only if the soil was dry did one pass have little effect on the
soil density at a depth of four to seven inches. Continued traffic over
the same area, however, did compact a dry soil to this depth. Only on
the Sims soils did 25 passes compact the subsoil at a depth of ll-lh

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- 66 -

The results of this compaction study are also shown graphically
in Figure XI. An examination of this Figure reveals that in most cases
the curves have a steeper slope between one and five passes than between
five and twenty-five passes. This clearly shows that the greatest
amount of cOmpaction was caused by the first passes.

Attention should also be called to the rather large number of
instances where the bulk density after traffic was less than that of the
undisturbed soil. This was most evident after one pass at the four to
seven inch depth. Whether or not these differences represented sampling
errors or were related to the negative pressures reported earlier is
unknown at this time.

The effect of soil moisture on soil compaction was so strong that
with the data available it was impossible to demonstrate the effect of
soil bulk density. However, since the bulk density was found to affect
the pressure distribution, it would also be expected to influence the
compaction pattern. In general, additions of pressure to soils with a
naturally high bulk density will not effect as much change in the bulk
density as in soils whose normal density is less.

At several locations a "furrow" was made by stripping off the
top four inches of soil. The tractor wheel was run in this channel and
the bulk density of the soil at the four to seven inch depth compared
to bulk density of the soil at the same depth but where the tractor had
passed over the soil surface. These data are shown in Table 20.

Without exception the soil in the "furrow" was more compact than
soil at the same depth, but four inches further removed from the tractor

tire. This emphasizes two points: (1) pressure is dissipated rather

p

BULK DENSITY (gms.per cc.)

-67-

 

 

 

L70]
0 4
I60
/° 0 ID
0 5M
|.50‘ ° IM
0
L404
0 0 5W
70 2w
° 6
. 0 ° 20
n w — war
I u - uousr
' o — DRY
l.20 l 1
I 5 25

NO OF PASSES

Figure XI - Effect of tractor traffic on soil
bulk density. Identification numbers refer to sites
given in Table 2.

 

~68-

rapidly in soils; (2) pressure under a tractor wheel which is in a fur-

row while plowing may cause considerable compaction.

TABLE 20

BULK DENSITY OF SOILS M‘IEN COMPACTED AT TWO
DEPTHS BY A FERGUSON warm

 

 

 

 

Treatment
Soil Moisture Normal Surface Pass Furrow Pass
Percent
Hilladale 1705 10,49 1.146 1055
sandy loam
Conover loam 18.8 1.h8 1.39 l.h8
Brookston loam 28.1 1.29 1.30 1.140
Berrien 1h.8 1.52 1.117 1.52
sandy loam
Berrien 22.9 1.110 1.16 1.118
sandy loam
Brookston loam 17.8 1.31 1.3).; 1.142

 

The second conclusion may not always follow in practice since in
many cases the subsoil is frequently present at plow depth. Subsoils
are often more dense than surface soils and hence suffer less compaction.
m the other hand they may be more moist and more vulnerable to compac-
tion. Any increase in the bulk density of a soil is to be guarded against.
Compact subsoils are particularly undesirable because they have deleteri-
ous effects on plant growth and because they pose difficult soil manage-

ment problems.

- 69 -

In addition to the tractor as a compacting instrument, the D-h
Caterpillar and the ton pickup truck were used. A comparison of the

relative compacting effects of the truck and tractor may be seen in

 

 

 

 

Table 21.
TABLE 21
COMPACTION PRODUCED BY TRUCK AND TRACTOR
Vehicle Tractor Truck
Soil Moisture Depth Passes O l 0 1
Inches Bulk Density
Sims sandy Moist 0-3 1.18 1.32 1.18 1.38
clay loam
h-7 1.13 1.23 1.13 1.32
sandy loam

 

It is evident that an empty pickup truck compacted the soil to a
greater extent than did the tractor. A reflection on the pressures under
each vehicle as recorded earlier in this report reveals that this re-
lationship is logical.

Another interesting comparison involves the Caterpillar and Ferguson
tractors. A deep tillage demonstration in connection with the Centennial
of Farm Mechanization brought together several makes of tractors. Advan-
tage was taken of this situation to compare a representative of the wheel-

and crawler-type tractors.

 

 

- 7o -

The soil conditions unfertunately'were not too desirable. The site
had.previously been plowed and disked. The surface soil was quite loose
and dry. To take the cores in the surface soil the top two inches had
to be scraped off. The sample at the deeper depth.was taken in the un-
plowed sons. The bulk densities are shown in Table 22. The Caterpillar
treads apparently loosened.the surface soil unless a load was being
pulled. The important conclusion to be reached from these data, it is
believed, is that the crawler-type tractors may cause considerable soil
compaction in spite of the fact that manufacturers' specifications indi-
cate small surface pressures. These compaction data further point out
that the effects on compaction as thus far reported are probably'minimnm.
effects and that compaction may be expected to increase as the draft
load is increased.

TABLE 22

CHANGE IN BULK DENSITY 0F BROOKSTON LOAM
DUE TO TRACTOR TRAFFIC

 

 

 

 

 

 

 

vehicle Ferguson Caterpillar
Passes Passes
Moisture Depth 0 1 13 5 0 1 1“ 5
Percent Inches Bulk Density

 

20.5 2-5 1.17 1.20 1.20 1.21 1.18 1.12 1.21 ' 1.23
23.0 6-9 1.20 1.19 1.23 1.31 1.18 1.18 1.25 1.26

 

a Pulling deep tillage tool.

- 71 -

Laboratory. Soil cores taken at the same time as those used in
measuring compaction in the field were brought into the laboratory.
Pressure was applied to the cores by the apparatus shown in Figure VI.

During the progress of this portion of the investigation, several
facets of taking and compressing the cores were explored. It was fOund,
for instance, as can be seen from Table 23, that the initial compactive
state of the soil affected the change in bulk density produced by the
applied pressure. It was thus necessary to obtain undisturbed (natural)
soil cores for laboratory compaction. The variability between cores
was small and it was not found necessary to compact more than five cores
at each pressure.

TABLE 23

EFFECT OF INITIAL STATE OF COMPACTION ON THE CHANGE
IN BULK DENSITY WITH APPLIED PRESSURE

 

 

 

 

Pressure
Pounds Per Square Inch
Treatment 0 25 50 75
Undisturbed 1.07 1.15 1.20 1.23
Two passes 1.32 1.36 1.39 1.111

 

Using the field compaction data as a basis, it did not appear in
the early studies that the compaction produced in the cores was commen-
surate with the applied pressure. It was thought that arch action - the
tendency of a soil to vector out or distribute a compressive force -
might be involved and that some of the compressing force was being lost

due to friction and absorption at the soil-cylinder interface. Berdan

-72..

and Bernhard (h) in compacting a soil using a modified Proctor technique
found that the curves of equal soil density went towards the cylinder
walls, indicating that the pressure was being vectored out.

The inside wall of some cylinders was lubricated in an effort to
reduce arch action. The effect which this application of grease had
when used with a coarse and medium textured soil may be seen in Table 2h.
In most cases the change in bulk density was greater when the cylinders
were greased, but the differences were not considered of sufficient mag—
nitude to materially disturb the comparisons desired. Berdan and Bern-
hard (h) have found that the maximum compaction density is not reduced
by confining effects.

The interval of time during which the pressure was applied to the
soil core was found to affect the ultimate compaction. As can be seen
from Table 25 the application of pressure once for 13 seconds caused the
same change in compaction as 25 one-second applications of pressure.
Thus, in a comparison involving the artificial loading of cores in the
laboratory and compaction in the field under wheels, it is important to
consider the time factor.

The bulk densities produced by applying a range of pressures to the
soil cores are presented on the right hand side of Tables 12 to 18. The
behavior of the soil in the cylinders was very similar to that in the
field, viz. increasing pressure caused increased compaction. The change
in bulk density was less when soils were dry than when they were moist.
One difference can be noted by comparing Figure XI with Figures XII to
XIV. The laboratory compaction more nearly follows the straight line

relationship reported by the United States Army Engineers (bl).

 

- 73 -

TABLE 2h

EFFECT OF LUBRICATING THE INSIDE OF SOIL CORES AT THE
TIME OF SAMPLING ON THE COMPACTION PRODUCED BY
APPLIED PRESSURES. PRESSURE APPLIED ONCE.

 

Change in Bulk Density

 

Mbisture Cores Cores
Soil Content Pressure Greased Not Greased
Sims sandy
clay loam

Surface soil 26% 25 .1h .09

50 .20 .20

75 .2h .22

100 .37 .31

Subsoil 18% 20 .07 .Oh

ho .1h .07

60 .18 .16

80 .11 .
Hillsdale
sandy loam

Surface soil 19% 25 .07 .09

1 SO .11 .08
75 .12 .1h

100 .20 .17

Subsoil 17%% 10 .03 .01

20 .05 .03

’40 .05 003

80 .09 .09

 

 

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w
w " WET
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D» DRY
l I
I 5 25

NO. OF TIMES PRESSURE APPLIED

Figure XII - Compaction produced by twenty-five
pounds per square inch pressure on soil cores taken at
a depth of zero to three inches.

BULK DENSITY (gms.per cc.)

L70-

I.60-

~76...

 

 

 

L30" o 20
:/° 6
,/ w- WET
u — MOIST
0 — DRY
LZG I I
I 5 25

NO. OF TIMES PRESSURE APPLIED

Figure XIII - Cempaction produced by fifty
pounds per square inch pressure on soil cores taken
at a depth of zero to three inches.

BULK DENSITY (gms.per cc.)

L70]

l.60-

l.50‘

L40-

L30‘

-77..

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. ’7 50
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LZO

r j

5 25
NO. OF TIMES PRESSURE APPLIED
Figure XIV - Compaction produced by twenty

pounds per square inch pressure on soil cores taken
at a depth of four to seven inches.

-78..

The change in bulk density was plotted against the applied pressure
for the soils at each location. From these curves the pressure was ob-
tained for the change in bulk density equal to that change produced by
one pass of the tractor. These pressures are recorded in Table 26. The
average maximm pressure recorded by the load cells under a rear tractor
wheel at all sites at the three and seven inch level is also given at
the bottom of the table. It can be seen that this average and the aver-
age of the pressures reported in the Table agree very closely. It is
concluded, therefore, that the soil pressures as recorded by the test
cell as described and used in this study are quantitatively reliable.
Furthermore, the use of soil cores for estimating the susceptibility

of soils to compaction by applied pressure is satisfactory.

 

 

-79..

TABLE 26

PRESSURES REQUIRED TO PRODUCE THE SAME COMPACTION IN SOIL CORES
AS WAS PRODUCED BY FERGUSON TRACTOR TRAFFIC

 

 

 

Surface
Moisture Depth in Inches
Soil Content 0-3 —7
% Pressure in pounds/square inch
Hillsdale sandy loam 18.6 65 15
n n n 1h.8 15 10
u n n 20.0 55 10
Berrien sandy loam lh.0 60 _a
" " " 22.8 60 10
Brookston loam 28.8 65 5
II In 111.5 25 _
Sims sandy clay loam 20.9 55 30
n n u n 25 o 8 15 .8.
n u n n 17.2 20 _a
Conover loam 19.6 10 -
Average hl 13

Average of maximum pressures
at 3" and 7" recorded by cells
under tractor traffic 31 19

 

a The bulk density after one pass was less than before, so no
comparison can be made.

SUMMARY AND CONCLUSIONS

The study herein reported was initiated to obtain information on
soil pressures resulting from traffic on agricultural soils and to
observe the relationship between those pressures and soil compaction.

To accomplish the objective 15 test cells using strain gages were
constructed. These were placed at different depths in undisturbed
soils of varying moisture content and texture. A variety of farm
implements and vehicles was passed over the cells and the pressure in
soils resulting from this traffic was recorded.

The effect of tractor and truck traffic upon soil compaction was
observed in seven soils by measuring soil bulk density at several depths.
Undisturbed soil cores were taken from the same soils at the same depths
and compacted in the laboratory. The pressure required to bring about
the same compaction in the cores as was produced by the traffic was noted.
This pressure correlated very favorably with the pressures measured by
the test cells.

The data presented indicate that for the soils used in this study,
pressures decreased very rapidly with depth. None were recorded below
16 inches. Furthermore, there is no evidence of pressures greater than
five pounds per square inch extending horizontally more than three or
feur inches outside the tire.

The maximum.pressure recorded at a depth of one and one-half inches
was about 150 pounds per square inch. This pressure was observed under

a ton pickup truck and a combine. The average pressure three inches

- 80 -

-81..

under the rear wheel of'a mediumpsized tractor was 30 pounds per square
inch. Pressure under small and crawler-type tractors was large enough
to cause significant compaction.

In addition to the effects of the vehicle, the pressure recorded
was also found to vary with vehicle speed, soil moisture, and soil
density. .Ample evidence is offered, it is believed, to indicate that
the pressure cells designed for and used in this study may be relied
upon to give an accurate indication of pressures in soils.

Laboratory compaction of cores was a satisfactory method of deter-
mining the effect of pressure on compaction and predicting the effect
of vehicle traffic on soil bulk density; Such compaction revealed that
pressures as little as ten pounds per square inch may be effective in
compacting soils. Pressures of this magnitude were encountered to a
depth of ten inches under all vehicles,

It is the opinion of the author that the "plow pans" existent in
so many of our soils are due to traffic and not tillage. To prevent
soil compaction and all the harmful results accruing therefrom.(restricted
root zone, increased runoff and erosion, limited aeration, etc.) agri-
culturists must‘be cautioned to eliminate all unnecessary traffic and to
avoid travel over the soil when the moisture content is high.

It is suggested that parallel with this action agricultural equip-
ment manufacturers consider the large detrimental influence of modern
designed machines on compaction and explore ways of reducing unit sur-

face pressure.

L _

N
o

3.
h.

S.

7

9.

10.

12.

13.

LITERATURE CITED

Alexander, L. T. Soil as a physical system, Agronomy 2, (Soil
Physical Conditions and Plant Growth). Academic Press, New
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Bacon, C. A. Some physical aspects of organic matter. Ag. Eng.
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Baver, L. D. Soil Physics, pp. h2h—25. John Wiley, New Ybrk. 1956.

Berdan, D., and Bernhard, R. K. Pilot studies of soil density
measurements by means of X-rays. Proc. Am. Soc. Test. Mat. 50:
1328-h2. 1950.

Bernhard, R. K. Static and dynamic soil compaction. Pros. Hwy.
Res. Board, Pp. 563-920 Dee. 1951.

Blake, G. R., and Aldrich, R. J. Effects of cultivation on some
soil physical properties and on potato and corn yield. Soil Sci.
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Buses, Otto. Bertrag zur methodik der diagnostizierung verdichteter
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auf schweizerischen ackerboden. Landw. Jahrb. Schweiz. 6hxl-68.
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Cooper, A. w. Personal communication.

DenHartog, J. B. Strength of materials, pp. 206-8. McGrawbHill,
New York. l9h9.

Doneen, L. D., and Henderson D. W. Compaction of irrigated soils
by tractors. Ag. Eng. 3hx9h. 1953.

Free, G. R. Traffic soles. Ag. Eng. 3h:528. 1953.

Free, G. R., Lamb, J., and Carleton, E. A. Compactibility of
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Soc. Agron. 39:1068. l9h7.

Gill, W} R., and Reeves, 0. A. The compaction patterns of smooth
rubber tires in Hiwassee sandy loam. Submitted for publication.

Huberty, M. R. Compaction in cultivated soils. Trans. Am. Geophys.
Union 25:896-899. 19th.

- 82 -

 

15.

16.

17.

18.

19.

21.

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2h.

25

26

27.

28.

-83-

Jamison, V. C. Heavy machinery'- New problems in soil management.

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Jamison, V. 0., weaver, H. A., and Reed, I. F. Distribution of

tractor tire effects in Cecil clay.
15 33’4‘37 o 19500

Soil Sci. Soc. Am. Proc.

Lutz, J. F. Mechanical impedance and plant growth, Agronomy 2,
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(Soil Physical Conditions and Plant
York. 1952 e

140016311, D. J., and Williams, F. H. P.

Research on soil compaction

at the Road.Research Laboratory; Proc. Second Intn'l. Conf. on

Soil Mechanics. 19h8.

Merkle, F. G., and Kardos, L. T. Soil structure problems in
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RMA-NE-ll, January'l, 1955.

Neal, 0.11., Brill, G. D., Blake, G.

R., and Springer, D. K.

Res. in methods of soil and water conservation in N. J. Ann.

Rpt. 1950.

Nichols, M. L. Methods of research in soil dynamics as applied to
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Parker, E. R., and Jenny, H. water infiltration and related soil
properties as affected by cultivation and organic cultivation.

Soil Sci. 60:353. 19h5.

Philippe, R. R. Field compaction. Proc. M. I. T. Conf. on Soil

Stabilization, pp. 162-67. 1952.

Reeves, C. A., and Nichols, M. L. Surface soil reaction to pressure.

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Ag. Eng.

Reed, I. F., and Berry, M. D. Equipment and procedures for farm

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19h9.

Richards, S. J. A soil penetrameter.
6:10h-7. 19h1.

Robertson, L. S., and Hansen, C. M.
Ag. Expt. Sta. Q. Bul. 33:1—h. 1950.

Soil Sci. Soc. Am. Proc.

A recording penetrometer.

Ago Eng. 30 367“7o o

Mich.

 

29.

31.

32.

33.

3h.

35

37.

38

39.
ho.

h2.

h3

Q

-m-

Russell, M. B., Klute A., and Jacob, W. C. Further studies on the
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1952.

Snyder, F. W., and French, G. Manuscript submitted for publication.
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der Landtechn. 1:87-9h. 1951.

S3hne, V. W. Die kroft ubertragung zwischen schlepperreifen und
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SShne, V. W. Druckverteilung im ackerboden und verformbarkeit des
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S3hne, V. W. Druckverteilung im boden und bodenverformung unter
schlepperreifen. Grdlgn. der Landtechn. 5:149-63. 1953.

 

Stone, A. A., and Williams, I. L. Measurement of soil hardness.
Ag. Eng. 20:25. 1939.

Struchtemeyer, R. A. An investigation of the effect of field traffic
and Maine winters on the physical condition of the soil. Progress
Report Soil Structure Research RMA-NE-ll, January 1, 1955.

Taylor, D. W. Fundamentals of soil mechanics, pp. 566-71. John
Wiley, New York. 19h8.

Terry, C. W., and Wilson, H. M. The soil penetrometer in soil
compaction studies. Ag. Eng. 3&2831. 1953.

Tharp, F. C. Personal communication.

Uhland, R. E., and O'Neal, A. M. Soil permeability determinations
for use in soil and water conservation. Soil Conser. Ser. Tech.
Pub. 101. 1951.

United States Army, Corps of Engineers. Soil compaction investiga-
tion report No. b, 1950.

vanden Berg, G. E. Measurement and analysis of soil pressure dis-
tribution under tractor and implement traffic in an artificial
field. Master's Thesis. Michigan State University. 1956.

Veihmeyer, F. J., and Hendrickson, A. H. 3011 density and root
penetration. Soil Sci. 65xh87-h93. 19h8.

 

hh.

h5.

h6.

h7.

- 85 -

Vomocil, J. A. In situ measurement of soil bulk density. Ag. Eng.

35:651-5h. 195k.

Vomocil, J. A. Gamma ray densitometry and its use in evaluation
of soil physical condition. Ph.D. Thesis, Rutgers University. 1955.

weaver, H. A. Tractor use effects on volume weight of Davidson loam.

Ag. Eng. 31:182. 1950.

weaver, H. A., and Jamison, V. 0. Effects of moisture on tractor

tire compaction of soil.

Soil Sci. 71:15-23. 1951.

 

 

APPENDIX

A sample of the pertinent data obtained for each site where pressures
were recorded is listed below. Table 27 illustrates how the recorded
pressures were tabulated. Tables 28 to 37 contain the summaries of all
the individual tabulation sheets.

 

 

 

 

Date: August 26, 1955
Location: College Farm
Soil: Spinks sandy loam Test Recorder
Moisture Depth Cell No. Depth Channel No.
III. In.
15.5 0-3 111. 3‘ 1
13.6 3-6 109 h-3/h 2
13.5 6-12 107 6-5/8 3
11.5 12-18 110 10 h
108 111-7/8 5
106 1-7 8 6
TABLE 27
SAMPLE COPY OF TABULATION SHEET
Displacement Strai load
Run Tire Channel (Inches)b (Microinches)° (Pounds c
No. Pos.a vehicle No. Front Rear Front Rear on Rear
7 hN Cat. 1 -.1h0 ~13.6 (-)
2 .120 12.14 110
3 -.100 -12.h (-)
h -.068 - 6.6 (-)
5 .100 8.0 20
6 -9062 -605 (-)
8 IN Combine 1 .395 38.7 175
2 .360 37.1 105
3 .265 32.9 95
h .030 2.9 5
5 .109 8.7 20
6 .380 39.8 130
—.O82 -8.6 (-)

 

a In this and subsequent tables tire position indicates the direction
and distance in inches from the tire outside to the "zero" line.

b Obtained by measurement of peak heights from the Hathaway traces.

° Strain and load were obtained by using the instrument and cell cal~
ibration factors, respectively.

- 86 -

 

_ 87 -

TABLE 28
SUMMARY OF IDADS RECORDED ON HILLSDALE SANBY 10AM
Date: June 15, 195k

Location: College Farm Moisture: Unknown
Soil: Hillsdale sandy loam

 

 

Tire Depth’in Inches

 

 

 

Vehicle Pos. 3‘ 3‘ 3 3 7 3 7U
Pressure in Pounds
Ford 0 0, 300 0,215 (-),(-)a 0,0 0,(-) 0,0 0,0
Tractor 2N -, 20 -,180 - ,(-) -,0 -,(-) -,0 -,0
0 ‘2 ho “3305 ' 9 30 'a(') ‘9(‘) “:50 O,(- )
Zn '3 20 ”3215 ' 9(') ’9(‘) ‘3(') '90 0:0
hN ‘9 10 '9 20 ‘ :(‘) ”:0 '9(‘) ‘9(‘) 0:0
6N -, 0 -, 0 - ,(-) -,0 -, 0 0, 0 0,0
28 ‘9 8 ‘5305 ‘ :(‘ ”9&5 -,ho '97 O,(- )
us 0,110 0, 50 (-),200 0,165 0,60 0,100 (- ),0
pit 60,(-) 0,0 70, 0 115,0 25,h5 25,25 15,55
Case 0 30 230 30 (-) 15 60 (-)
Tractor 3M 20 70 (-) 0 (~) (-) 0
6N 0 0 (-) 0 (-) (-) 0
25 100 160 180 115 50 90 (-)
25 75 200 135 50 20 65 15
us 100‘ 100 165 195 65 100- (-)
pit (-) 0 0 0 50 20 A5
A1118 52 0,50 95,200 (-), 90 o, 65 0,15 0,25 0,(-)
Chalmers sh 0,05 100, 55 (-),105 0,120 0,20 0,30 0,(-)
Tractor 0 0,20 15,115 0 ,(-) (-),(-) O,(-) 0,10 0,1
N2 0,15 0, 70 0 ,(-) 0,0 0,(-) 0,0 0,0
Nb 0, 5 0, 35 0 ,(-) 0,0 0,0 0,0 0,0
pit 0,(-) 0, 0 0 , 25 0,50 0,25 0,25 0,30
TruCK N6 0:10 20: 25 ('):(') 0:0 (‘)9(‘) (‘):(') 0:0
Nu 10:10 105) 75 ('):(‘) 0:0 (')9(‘) (')3(') 0,0
N2 20,20 2&5.205 (~).(-) (- ),(- ) (-),(-) (-).10 (-),(-)
O 35:50 225, 215 1902160 (')’(‘) 20:20 30,h0 (‘)9(‘)
52 110,110 95, 95 300,300 195,170 50,50 50,50 (-),(-)
Sh ' 9 ' 35:15 195,235 280,260 60,60 h59h5 ('):(')
pit - , - 0, 0 ho, 70 100,210 55,70 35,60 (-),(-)

 

8 Cell in horizontal position.
b Cell in disturbed soil (tamped backfill of pit).
0 Pressure under front and rear wheel, respectively.

-88..

TABLE 29

SUMMARY OF LOAIB RECORDED 0N HIILSDALE SANDY LON/I

 

 

 

 

 

 

Date: July 16, 195k Moisture Depth

location: College Farm % In.

Soil: Hillsdale sandy loam 12.0 0-2

1,405 h”?
16. 10-12

Tire Depth in Inches

Vehicle Pos. 2 7 12 T“

Pfessure in Pau-nas

Tractor 0 0,0 0,0 10, 0,0
0 0,0 0,0 10,20 0,0
0 0,0 0,0 15,30 0,0
0 0,0 0,0 15,25 0,0
0a 0,0 0,0 15,20 0,0
31 0,0 0,0 10,20 0,0
31 0,0 0,0 10,25 0,0
51 0,0 0,0 15,20 0,0
31 0,0 0,0 10,15 0,0
31a 0,0 0,0 10,15 0,0
52 0,0 0,0 10,15 0,0
52 0,0 0,0 5,15 0,0
52 0,0 0,0 10,15 0,0
52 0,0 0,0 10,15 0,0
32a 0,0 0,0 5,10 0,0
53 0,0 0,0 15,15 0,0
53 0,0 0,0 0,10 0,0
53 0,0 0,0 5,10 0,0
33 0,0 0,0 5,10 0,0
sh 0,0 0,0 5,10 0,0
sh 0,0 0,0 0, 5 0,0
sh 0,0 0,0 0,10 0,0
55 0,0 0,0 0, 5 0,0
55 0,0 0,0 0, 5 0,0
N1 10,0 0,(-) 20,25 0,0
N1 0,(-) 0, (') 15325 0:0
N1 0,15 0,(-g 20,20 0,0
N1 10,10 0,(- 15,30 0,0;
N1a 30,30 0,0 10,25 0,0
N2 0,0 0,0 20,30 0,0
N2 35,30 0,(-) 20,30 0,0
N2 15,20 0,(-) 15,30 0,0
N2 30,30 0,(-) 15,30 0,0
N2a 80,30 o,(-) 10,20 0,0
N3 30,0 0,0 10,30 0,0
N3 ho,h5 0,10 10,25 0,0
N3 25,u0 0,0 15,20 0,0

 

TABLE 29 (CONTINUED)

~89-

 

 

 

 

Tire Depth in InEhes

Vehicle Pos. 2 7 12 6"

Pressure in Pounds

Tractor N3 30,25 EZET“""‘EKE30" 0,0
N3a u5,25 0,0 5,20 0,0
Nh 60,60 0,10 15,25 0,0
Nh 80,100 15,10 5,15 0,0
Nh 95,55 10,10 10,25 0,0
N1 85,60 10, 5 10,25 0,0
Nua 85,80 10, 0 5,20 0,0
N5 80,90 10,15 5,20 0,0
N5 h5,90 10,15 10,20 0,0
N5 80,125 10,15 10,20 0,0
N5 75,75 10, 5 10,15 0,0
NSa 100,110 10,10 10,20 0,0
N6 100,125 20,20 10,15 0,0
N6 100,135 15,20 10,20 0,0
N6 85,125 20,20 5,20 0,0
N6 110,125 10,20 5,15 0,0
N8 0,110 0,25 5,15 0,0
N8 25, 75 10,20 5,15 0,0
N8 80, 90 10,20 5,10 0,0
N12 0, 0 0,0 0,0 80,60
N12 0, 0 0,0 0,0 60,65
N12 0, 0 0,0 0,0 60,60
N12 0, 0 0,0 0,0 60,60
N12 0, 0 0,0 0,0 65,60

Truck 53 0, 0 15,20 25,20 65,60
52 10, 0 20,20 10,30 65,60
51 0, 0 15,20 35,30 65,60
0 0, 0 20,15 30,30 65,60
N1 0, 0 0,0 h0,h0 65,60
N2 55,50 20,0 30,80 65,60
N3 115,135 20,10 h0,30 65,60
Nu. 185,185 10,30 30,30 65,60
N5 260,230 55,10 30,30 65,60
N6 290,270 65,65 20,20 65,60
n8 115,110 50,h0 15,10 65,60
N10 35,u5 30,25 10,10 65,60
N12 0,0 10,15 0,0 65,60

 

a Test run made at fast (w 5 mph.) vehicle speed.

 

 

TABLE 30

SUPD’IARY OF LOADS RECORDED ON SIMS CLAY LOAM

 

 

 

 

Date: August 1, 195h Moisture Depth
Location: Ferden Farm % In.
Soil: Sims clay loam 13.5 0-6
11.8 6-9
10.5 9-12
9.8 12-18
Tire Depth in Inches
Vehicle Pos. 0 3 3a ca 0 7 1E
, Pressure in Pounds
Tractor hN 0,0 0,0 (-),65 0,h0 0,0 0,0 0,0 0,0
hN 0,0 0,0 (-),70 0,80 0,0 0,0 0,0 0,0
3N 0,0 0,0 0 ,30 0,30 0,0 0,0 0,0 0,0
3N 0,0 0,0 25,0 0,3 0,0 0,0 0,0 0,0
2N 0,0 0,0 35,125 15,35 0,0 0,0 0,0 0,0
2N 0,0 0,0 0,60 10,35 0,0 0,15 0,0 0,0
1N 0,0 0,0 (-),80 15,u5 0,0 0,15 0,0 0,0
1N 0,0 0,0 (~),110 15,u0 0,0 0,0 0,0 0,0
0 0,0 0,0 (-),120 15,u0 0,(-) 0,15 0,0 0,0
0 0,0 0,0 (-),130 15,85 0,(-) 0,20 0,0 0,0
18 0,0 0,10 (-),130 10,u0 0,0 0,20 0,0 0,0
13 0,0 0,0 65,160 20,35 0,(-) 0,25 0,0 0,0
as 0,0 0,55 80,100 0,0 0,0 0,20 0,10 0,0
as 0,65 0,25 90,1b5 0,10 0,0 0,30 0,10 0,0
35 0,65 0,u0 75,95 0,0 (-),15 0,30 0,20 0,0
33 0,0 0,10 80,150 10,15 0,0 0,25 0,10 0,0
us 0,0 0,u5 90,1h5 0,0 (-),(-) 0,25 0,15 0,0
ts 0,0 0,10 85,150 10,0 (-),0 0,25 0,0 0,0
55 0,120 0,35 80,120 0,0 (-),30 0,30 0,20 0,0
53 0,100 5,55 80,90 0,0 (—),0 0,30 0,20 0,0
65 0,100 5,30 70,130 0,0 0,10 0,30 0,20 0,0
65 0,90 5,00 65,125 0,0 0,u0 0,30 0,20 0,0
75 0,60 5,70 80,110 0,0 30,50 0,30 0,25 0,0
73 0,80 5,15 65,120 0,0 30,25 0,30 0,25 0,0
as 0,15 5,105 55,55 o,o 35,50 0,35 0,25 0,0
83 0,15 0,100 50,90 0,0 (-),50 0,30 0,20 0,0
95 150,60 20,100 0,25 0,0 35,55 0,25 0,20 0,0
95 150,60. h5,105 0,0 0,0 35,u5 0,20 10,25 0,0
105 160,170 35, 0,25 0,0 25,h0 0,20 0,25 0,0
105 30,h0 35,90 0,0 0,0 35,55 0,20 10,20 0,0
113 100,125 25,30 0,0 0,0 35,u0 0,25 0,20 0,0
113 90,70 35,20 0,0 0,0 25,u0 0,20 10,25 0,0
123 0,0 0,0 0,0 0,0 25,30 0,20 10,20 0,0
123 70,0 20,35 0,0 0,0 25,35 0,0 10,20 0,0
133 0,0 10,0 0,0 0,0 15,25 0,20 10,25 0,0

 

r

TABLE 30 (CONTINUED)

 

 

 

 

 

_ Tire Depth in Inches
vehicle P05. 0 3 Ba 6‘ 35’ 712% 17
Pressure in Pounds

Tractor 135 0,0 0,0 0,0 0,0 25,25 0,0 10,20 0,0
1&5 0,0 0,0 0,0 0,0 10,25 0,0 10,15 0,0

lbs 0,0 0,0 0,0 0,0 15,20 o,o 10,10 0,0

155 0,0 0,0 0,0 0,0 0,0 0,0 10,0 0,0

155 0,0 0,0 0,0 0,0 0,25 0,0 10,0 0,0

us 0,70 0,50 80,95 0,0 (-),15 0,35 10,25 0,0

55 0,15 0,70 75,90 0,0 (-),25 0,35 10,25 0,0

65 00,65 0,90 h5,60 0,0 25,30 25,20 10,25 0,0

Truck 59 0,0 15,0 0,0 0,0 60,15 20,0 25,0 0,0
58 0,0 30,0 0,0 0,0 55,15 20,0 20,0 0,0

57 50,0 80,0 0,0 0,0 85,25 25,0 30,15 0,0

56 310,0 180,h5 35,0 0,0 90,h5 35,0 30,20 0,0

55 30,0 30,10 0,0 0,0 35,25 20,0 20,1 0,0

sh 380,60 210,60 0,0 0,0 75,50 to 20 30,25 0,0

53 h00,70 170,85 50,0 0,0 20,55 h0,25 30,25 0,0

52 290,270 150,130 75,0 0,0 75,60 u5,35 30,25 0,0

51 180,390 85,190 115,50 0,0 (-),65 55,h0 25,25 0,0

0 0,115 0,90 315,115 u0,0 (-),0 35,h5 10,25 0,0

N1 15,300 30,150 190,60 0,0 (-),55 50,50 10,25 0,0

N2 0, 0 310,130 70,10 (-),(- 30,35 0,0 0,0

N3 0 0 115,275 90,h0 0,(-) 20,h0 0,0 0,0

Nh 0 0 25,260 h5,95 0,0 20,50 0,0 0,0

plow -. -- - -— -— 0,(-) 0,0 0,0

 

a Cell in disturbed soil (tamped backfill of pit).

b Cell in horizontal position.

 

Unknown

Moisture:

_ 92 i
TABLE 31
SUMMARY OF TIILAtE mm, AUGUST, 1951.

August 17, l95h
College Farm
Hillsdale sandy loam

 

 

Location:
Soil:

Date:

 

9-3/h 10

in Inches
9%

New
7%

 

Pos.

Implement

Pressure in Pounds

 

 

’
3

0 0
O O
0: (')

pre-plow
plow
after plow

Flow

5
102

505

’3’
000
O

o.)

9
000

0(0
000

Disk
Disk
Disk

 

spring

Harrow
tooth

 

 

 

 

0.0 $.05 0.3 3.3 5.0 .80.
0.0 0.0 0.0 0.0 0.0 read
0.0 mm.0 A-V.0 0.0 0.0 u- u. -n -- eofle-e 0
0.0 A-V.A-V 0.0 0.0 me.0 A-V.0 0.0 0.0 0.0 Nam
0.0 AtV.Auv mH.0 0m.0 00.0 0.0 0.0 mH.0N 0.0 0am
0.0 0.0 0m.0m 0.0a 00H.0a mHH.00H 00.Aav 0.0: m0~.mH 0m
0H.0 0.0 0m.0r m:.0m m0.me 0ma.0ma maH.0 0.me mm.me mm
0.0 0.0 mm.mm 0.00 00.00 moa.0ra m0H.0 mH.0s 00H.mm em
0H.0 0.0 mm.0m 0m.m0 0~.0a 0.maa m0.0 0.05 mom. .00H 0a
0.0 0.0a 0m.0m 0.0 0s.mo 0d.00H 0.0 0.m~ 0am. 05M mm
0.0 2.9.. 2.3. 0.0 more 3.00 3.0 3.3 8nd: 5..
. 0.0 0H.mm 0.0 0.0 00.mm 05 0.0 A-V.A-V 000.0m mm
.3 0.0 0m.mm 0H.A-V 0.0 00.mm A-V.Auv 0.0 A-V.Anv mma.0m «a
o, 0.0 00.00 0H.Atv A:V.A-V Auv.0m 0.A-v 0.0 A-V.Auv ma.0m Hm
. 0.0 mH.mN 0.“-3 0.0 0.Atv 0.0 A-V.A-v ome.0m 0
0.0 0m.mH 0H.Auv A-V.Anv Auv.ms A-V.0 0.0 A-V.Auv 0:0.mm H2
0.0 mm.mm Auv. 0 0.0 0.0 0.0 AIV.A-V 0.0 m3 aces»
0.0 mm. 00 any. 0 0.0 0.0 0.0 AIV.0 0.0 m3 leads
0.0 0m.mm A-V.Auv 0.0 0.0 0.0 0.0 0.0 0.0 as etch
mvgom sun enzwmeum
mxausa :\H-0H m emNHna on. e: em\aum exasm «\H. .eom oaonooe
someoH on ossom cane

 

 

seem eaonessesm .Hnom
goEED ”maniacs nowpmpm. 9:05.33 0x3 emom 303003
emea .ma peruse .0500

050 330205 zo 0000005 09.8 0 gm

mm mama.

 

.00900000 on 00¢ hue 000500000 00000 02000090 0 pom 0>hso soapmnn0amo 0000 A

.00000000 0000000000 00 0000 0

 

 

 

- 0-0H00 0m. .00 00H00 0- 0. ? 0 - - - - 2000 00000
.. 0.0.0-0 .0 o. 0.0 00 .. n 0 -- .000.
00.0 00.00 00.0 0-0.0-0 00. .0 0.0 00.0 0.0 000
00.0 0H0 00.00 00.00 00.00 000. .000 0.0 00.00 0.0 00
. 00 0 00 0 00.00 000.00 00.00 000. .000 0-0.00 00.00 00.00 0m
0m 00.0 00.0 00.00 000.00 00.00 000. 000 00.0 00.00 000.00 00
_ 00.0 00.0 00.00 000.00 00.00 000.000 00.0 00.00 000.000 00
00.0 00.0 00.00 000.0 00.00 000.000 00.0 00.00 00.000 00
00.0 00.0 00.00 000.0 00.00 000.000 0.0 00.00 000.000 00
00.0 00.00 00.0-0 00.0 00.00 000.0-0 00.0 00.0-0 000.00 00
00.0 00.00 00.00 00.0 00.00 000.00 0-0.0-0 00.0-0 000.00 00
00.0 00.00 00.3 00.0 00.0 000.0 3.0 00.3 000.0 00
00.0 00.00 00.0-0 00.0 00.0 000.0 0.0 00.0-0 00.00 0
00.0 00.00 3.3 00.0 3 .00 000.3 3 .0 3.3 00.00 S
00.0 00.00 00.0 00.0 0.0 3 .3 000.0 0:
00M0 00.00 00.0-0 00.0 00.0 000.0-0 0-0.0 0-0.0-0 00.0 03
00 0 00.00 00.00 00.0 0.0 0-0.0 0.0 0-0.0 00.0 0: 00000000
qupom 00 mnummwnm
000.00 0\0no0 ‘00 00\0-0- 00 00‘ 0000-0 000.0 000 .000 0000000

 

000000 00 00000

AQHDZHHZOOV NM mumdy

0000

 

 

- 95 -

TABLE 33;

SUMMARY OF LOADS RECORDED ON HILLSDALE SANDY LOAM

 

 

Date: August 8, 1955 MOisture Dggth
Location: College Farm 5 In.
Soil: Hillsdale sandy loam 15.5 0-3
1h.6 3-9
13.1 9-15
Tire Depth in Inches

 

Vehicle Pos. 2-17D 3-1/8 5-1/h 7-3/h lO-S/B 15-1/2
Pressure in Pounds

 

Cat. 53 100 25 _50 100 30 10
s1 35 h5 75 85 30 15
N3 220 55 9o 55 65 25
N5 235 70 95 (-) 75 no
N7 200 90 95 (-) 65 35
N9 85 50 9o (-) 7o 25
Combine N1 210 130 165 9o 90 35
52 250 35 115 150 no 35
N1 220 150 315 h5 85 no
N3 390 190 235 no 75 30
Author 2 S G O 0 0 0

Depth in Inches
‘Ii37h 2-37u ’1-371 5-315 8-7/8 13-3Zh

Combine o 235 130 275 80 90 00
S1 350 205 205 120 90 35
$3 3ho 75 1&0 160 60 30

Car 0 65,80 105,110 50,20 35,10 0,10 20,20

31 60,110 (-), 65 75,60 60,30 30,5 25,20
s3 30,25 (-),(-) 15,35 h0,ho 25,15 20,20
N2 lOO,(-) 160,55 85,35 (-),(-) 20,20 20,15
N1 115,135 165,110 35,(-) 10,(-) 10,20 20,20

Tractor 52 (-),70 50,90 0,35 0,115 0,15 0,25
36 80,30 80,15 35,60 25,60 10,15 0,20
N3 " :(‘) ":15 '30 '3 (") '330 ”’0
N1 o,€-) 0,15 0,35 (-),(~) 10,35 0,20
0 (')3 ') 20:60 0:30 ("):(") 15:30 0:20
5]- ('):7S 25.9115 20:50 (‘):(') 10:30 0:25
S5 80,90 85,30 110,85 25,11 O,(~) 20,30

 

 

TABLE 3h

SUMMARY OF LOADS RECORDED ON SIMS SANDY CLAY 10AM

Date: August 12, 1955 Mbisture 232th

Location: Ferden Farm % In.

Soil: Sims sandy clay loam 27.0 0—7
20.9 7-15

 

 

Tire Depth in Incfies
vehicle Pos. 4I3172 2-7/8 ’h-7[8 6-3/h 9-7/8 15
Pressure in Pounds

 

 

Tractor E2 135,95 75,20 30,115 20,60 10,15 0,0
“3 (‘)s(') (‘)30 653100 0,(-) 0,0 0:0
10. (-),35 0,0 75,110 0,0 0,0 0,0
E5 h0,160 15,70 0,50 30,70 15,35 0,25
E8 50,110 10,65 (-),15 110,65 15,35 0,25
E7 ' 2110 '9 0 '9(‘ ’ :70 -,35 '225
Eb 90,90 50,35 0,80 35,80 15,35 0,25
E3 90,150 65,15 25,120 35,75 15,25 0,20
E6 h5,110 20,60 (-),50 h0,8o 15,35 0,25
0 85,120 15,(-) 85,160 25,55 ,1 0,0
E1 160,1b5 80,(-) 65,150 3o,u5 15,20 0,0
W2 (-),(-) 0,(-) 90,135 (-),(-) 0,0 0,0
E2 120,150 b5,60 25,9 us, 1 ,30 0,20
Truck E5 270,200 115,100 80,80 95,80 35,50 25,25
E6 135,150 85,85 80,85 80,80 35,35 25,25
E3 260,210 120,70 130,120 80,85 30,30 0,20
E1 210,2uo 35,u5 170,1h5 80,75 30,30 20,20
E2 320,230 115,55 150,155 85,85 35,30 -,20
Eh 160,160 70,70 75,h5 70,70 35,35 25,20
E6 150,150 50,50 30,30 60,65 35,35 25,25
E8 90,110 bo,ho 30,35 60,60 35,35 25,25
Pre-plow -) 0,(-) 0,(-)

0:(
Plow 0:0 0,(‘) O:(')

 

-97..

TABIE 35

SUMMARY OF LOADS RECORDED ON IRRIGATED SIMS SANDY CLAY LOAM

 

 

 

 

 

 

Date: August 12, 1955 Moisture Death
location: Ferden Farm 3 In.
Soil: Sims sandy clay loam 28.6 0-7
21.3 7-15
Tire Depth in Inches
vehicle Pos. 1-1/2 2.1/2 hrl/h ”597/8 9 Ih-I]2
Pressure in Pounds
Combine W1 560 180 110 120 50 (-)
Wk 90 100 35 15 55 25
E1 190 170 20 100 hS 0
E3 120 130 60 20 (-) (-)
E0 70 50 20 110 50 25
E2 200 175 lhO 105 30 15
W2 190 200 170 95 3o (-)
W3 175 35 1110 95 L10 0
vs 130 80 20 110 50 15
Tricycle 35 30 (-) (-) 0 0
wheel 90 20 (-) 15 10 o
Tractor W2 55,80 85,30 10,50 10,(-) 25,(-) o,(-)
w5 50,90 20,30 (4,25 20,15 0,30 0,0
0 70,70 15,65 25,10 20,0 0,0 0,0
E3 85: O 110:0”) ’45:)40 0: ("‘) O3(-) 0,(-)
E1 30:35 (‘):(') 25:25 (‘):(') ('):("’) 0, (')
0 100,90 50,(-) 115,)40 0,(-) 0,(-) 0,(-)
m. 105,70 15:15 60,115 10: (') 0,(-) 0, (')
“3 703125 50:50 03’45 20:10 30,(-) 0,(-)
Nb 75,95 50,10 0,50 30,20 30,30 o,(-)
75 55,85 20,50 (-),30 25,85 30,35 0,0
777 115,75 15,50 (-),(-) 20,115 0,35 0,25
Pre—plow 0,20 10,35 -,-
Plow -,- 0,10 0,0
After plow -,- 0,115 0,30

 

 

- 98 -

TABLE 36

SUMMARY OF LOADS RECORDED ON IRRIGATED SPINKS SANDY LOAM

Date: August 26, 1955 Moisture Depth

Location: College Farm 5 In.

Soil: Spinks sandy loam 17.0 0-5
16 n o it‘ll.
15.0 11,15
12.3 15-18

 

 

Depth in Inches

 

Tire
Vehicle Pos. 1-1/2 3-1/2 5-1/5 6e5/8 10-172 17

 

Pressure in Pounds

Truck N1 195,150 25,35 115,105 50,35 50,50 10,10

' N3 50,55 (-),(-) 30,10 5,5 35,30 15,10
51 200,155 25,20 50, 30 25,25 50,50 15,15

52 65,155 110,120 20,20 50,50 30,30 10,15

 

53 350,225 150,100 110,65 50,35 55,50 15,15

52 275,305 165,150 55,20 35,35 35,35 15,15
0 295,250 95,110 110,65 50,35 50,50 15,15
N2 395,300 160,155 55,55 50,35 35,50 15,15

N5 55,55 (-),(-) 15,10 0,0 35,30 15,15

Truck 31 280,525 115,185 15,110 20,65 15530
and 0 300,305 150,215 55,135 30,75 15,35
1 ton N1 300,315 110,185 60,160 35,80 15,35

load N2 335,355 105,195 60,160 : 35,85 15,35

0 335,310 155,215 70,165

Plow Pre~plow O,(-) O,(-) 0,55
Plow -, - ,0 0,0
After plow -, - O,(-) 0,0
Combine N1 375 70 185 65 9O 35
N3 265 50 - 180 55 80 35
SI 285 55 230 65 95 50
s3 150 200 165 55 8o 35
S3 355 20 190 95 95 35
N2 160 2 35 160 55 75 (-)
0 155 215 165 - 80 35
$2 310 15 155 - 9O 50

$5 75 (-) 10 - 50 30

TABLE 36 (CONTINUED)

 

Tire Depth in Inches
Vehicle Pos. 1-1/2 3-1/2 5-1Z5 6-5/8' 10-112 17
Pressure in Pounds

 

Tractor N3 0,55 30,35 35,85 20,55 0,50 0,0

N5 150,35 60,25 35,55 20,25 15,55 0,15

N1 (-),70 60,55 15,55 25,30 15,35 0,20

53 o, (-) 0,50 0,0 0,20 0,15 0,10

52 15,155 0,50 0, (-) 0,25 0,20 0,15

0 15,30 0,60 0,0 0,25 0,20 0,10

N3 0,175 50,60 5 ,10 2o, 30 15, 30 0,15

Plow Pro-plow -,- 0,20 0,10
Plow -,- 0,0 0,0

After plow -,- 30,25 10,25

 

- 100 -

TART-E 37

SUMMARY OF LOADS RECORDED ON SPINKS SANDY LOAM

 

 

 

 

 

Date: August 26, 1955 Moisture Depth
Location: College Farm 5 In.
Soil: Spinks sandy loam 15.5 0-3
13.6 3-6
13.5 6-12
11.5 12-18
Tire Depth in Inches
Vehicle Pos. I-7/3' 3 _5:3[5 6-5/8 10 15-7/8
Pressure in Pounds
Cat. N5 (-) (-) 35 (-) (- 20
N9 (-) 120 50 35 20 (-)
N1 (-) (-) 15 (-) 5 30
81 (-) (-) (-) (-) (-) 35
N3 (~) 30 25 25 (-) 30
N7 (-) 55 35 55 o 10
N11 115 65 55 3o 30 0
N5 60 50 60 50 15 20
Combine N1 130 175 105 95 15 20
N3 100 190 180 120 25 10
SI 25 155 125 110 25 20
SI 65 125 120 35 10 0
0 95 170 205 180 25 15
N2 150 105 95 30 20 0
N3 90 125 100 50 25 0
N5 150 120 95 50 35 (-)
TraCtor N3 (‘)920 (‘)930 (')920 (‘):(') (-),0 o:(')
N5 (”)330 (‘)950 (”>930 (")30 0,0 0:0
N1 (“)320 (- :(‘) ('):(‘) (')3(‘) (‘)3(‘) 0:5
N3 (‘) (‘)955 (")930 (')3O 0:0 0:5
N5 (-),30 20,30 0,30 0,20 0,0 0,0
N5 (“)335 ("):6S (“)3u5 ('):2o 0:0 0’0

 

 

 

 

 

Date Due

 

 

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