Ph.D. Thesis Academic Year 1990 Desa Ahmad An investigation into wetland soil-implement ...

452 Pages·2014·21.21 MB·English

CRANFIELD INSTITUTE OF TECHNOLOGY
SILSOE COLLEGE
Ph.D. Thesis
Academic Year 1990
Desa Ahmad
An investigation into wetland
soil-implement mechanics
Supervisor: Professor Spoor
G~
June, 1990
This is submitted for the degree of Doctor of Philosophy
the~is
in Agricultural Machinery Engineering .
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ABSTRACT
An investigation was initiated to obtain some
understanding on the behaviour of soil at higher moisture content
and to explore the potential of preparing paddy fields with
reduced amounts of water. This investigation comprised of three
separate studies.
Based on existing information that water could be
reduced when soil clods were initially formed prior to flooding,
the effects of clod size, clod initial moisture content and
confining states on the rate of water uptake were explored. The
moisture gradients within clods wetted and dried for different
period of times were also studied. The results of the clod
wetting experiments show that· the rate of water uptake by
capillarity was greatest when clods were initially very dry and
smaller clods tended to absorb water faster than bigger clods
when under confined conditions. Confining had no effect on
infiltration when the initial condition was very wet. On drying,
the smallest clod dried the fastest, reduced greater volume and
increased its dry bulk density significantly. Larger clods
required,longer drying period to arrive at a uniform moisture
profile within as compared to smaller clods. Results from the
wetting experiments were tested against the infiltration model of
.Jarvis and Leeds-Harrison (1987) and a model developed based on
linear flow of heat into a solid (Carslaw and Jaeger, 1959).
A second project involved the study of soil deformation
at high moisture contents in an attempt to produce clods with
minimum draught force using simple relieved tines at various rake
angles and depths in a soil tank. The principal. objective of the
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study was to utilise soil implement mechanics knowledge to
improve the efficiency of soil preparation for wetland crops.
Aspects like the nature of soil disturbance, extent of
disturbance and draught requirement were investigated. The soil
was in a plastic consistency prepared to three specified density
3
states of 940, 1000 and 1250 kg/m • The soil disturbance pattern
was monitored using implanted coloured beads and glass sided tank
studies. In addition, the extent and height of heave and surface
disturbance were noted.
Predictive models based upon Mohr-Coulomb soil mechanics
theory were developed to predict the interaction between the soil
and simple implements at three rake angles. These were based on
the lateral failure theory of Godwin and Spoor (1977) and the two
dimensional soil failure model of Hettiaratchi and Reece (1974).
Results from the single tine study were tested against the
models. A sliding resistance component and crescent effect were
incorporated to improve the predictions for the 45° and 90° rake
angle tines. The magnitude of each mode of failure is dependent
upon the critical aspect ratio which varies with tine rake angles
and soil conditions. The mode of failure is considered to be
lateral when the tine aspect ratio is larger than the critical
aspect ratio and an upward failure when the tine aspect ratio is
lower than the critical aspect ratio. The predicted results are
in close agreement with the results of the experimental studies.
For the backward raked tine, a model was developed based on the
formation of an elliptical wedge and bearing capacity type of
failure ahead and below the wedge. This failure theory was based
on the bearing capacity failure for deep footings. The model
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helped identify an additional parameter that influenced the
draught force for a backward raked tine. This parameter is the
sliding resistance component on both sides and beneath the
elliptical soil wedge •. Results from multitine studies showed that
draught force increased with tine spacinq but the increase was
not significant. In the wet condition the tines merely cut slots
and little or no interaction was noted.
In an effort to find the optimum water level for soil
puddlinq, a laboratory study was conducted to determine the
influence of water-soil ratio on the ease of puddling air dry
aqqreqates. Soil puddlinq was carried out usinq a·rotary stirrer
simulatinq the rotary motion of a rotary cultivator commonly used
in wetland preparation •. The results obtained showed that· the
fastest dispersion of particles resultinq in a minimum wet bulk
3
density of 1.23 Mg/m , was achieved at a water-soil ratio of 1.2.
(A supersaturated condition equivalent to a moisture content of
120% dry basis). Increasing the water-soil ratio above this value
did not change the wet bulk density value for all stirring times.
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ACKNOWLEDGEMENTS
The author acknowledges his sincere appreciation to Professor
G. Spoor for his invaluable advice and suggestions during these
studies and during the preparation of the thesis.
Gratitude is also expressed to Professor Dr. R.J. Godwin and
Mr R.F.A. Murfitt as members of the research committee and for
their personal involvement and encouragement at various stages of
the project.
A very special thank to Mr. Tony Reynolds and his team for
the assistance, suggestions and many hours spent in the
preparation of the soil and recording of the experimental data.
Thanks are also due to the soils laboratory technicians for their
assistance with the soil analysis and Dr. M.J. Q'Dogherty for
checking the tine prediction equations.
The author would also like to thank all other members of
staff of Silsoe College and fellow colleagues who have
contributed to the development of the project in one way or
another. The help rendered by Mr. Grant in deriving the complex
mathematical solution of the linear heat conduction model and Mr
Ademukum in sharing his computer programming expertise are
gratefully acknowledged.
The author is also indebted to Universiti Pertanian Malaysia
for the leave of absence and the Government of Malaysia for the
financial support. Last but not least, the author is extremely
grateful to his wife Wahida and children (Izwan, Ahmad Ashraf
and Muhammad Zhariff) for their patience, moral support and
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endurance without which this project could never have been
completed.
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TABLE OF CONTENTS
Page No.
.. . . . . . . .. . . . . . . . . . . . .. . . . . . . . . .. . .. .
Abstract •••••••••••• i
Acknowledgements .................................•....... iv
Table of Contents ....................................... . vi
List of Tables .......................................... . xii
.. .. .. . . . .. . . .. . . . . . . . . .. . . . . . . . . .. . . . . . .
List of Figures. xx
List of Plates •• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • xxvii
· . .. . .. . . . .. . . . .. .. . . .. .. . . . . .. . . . . . . . .
List of Sym1:;>ols. xxix
· .. . . . . . .. . . . . . . . . . . . . . .. . . . . . . .. . . .. . .
1.0 Introduction •• 1
·. . . . .. . . .. . . . . .. . . . . . . . .. . . . . . . . . . . . .
1. 1 GeneraL •• 1
~
1.2 Wetland Paddy Cultivation •••••••••••••••••••••••• 2
.......
1.3 Constraints To Improving Soil Preparation. 6
1.S Objectives....................................... 12
2.0 Literature Review •••••••••••••••••••••••••••••••••••• 13
2.1 Clod Wetting and Drying Studies •••••••••••••••••• 13
2.1.1 Rate of Water Uptake ••••••••••••••••••••••• 13
2.1.2 Shrinking and Swelling Behaviour ••••••••••• 15
2.1.3 Stability of Aggregates .••••••••••••••••••• 16
2.1.4 Clod Strength •••••••••••••••••.•••••••••••• 18
2.1.5 Modelling Water Infiltration Into Soil.Clods 19
.. . .. . . . . . . . . .
2.2 Soil Tine Interaction Studies .••••• 23
2.2.1 Soil Failure by Single Tines. 23
• • • • • • • • • • • • • •
2.2.1.1 Factors Affecting Draught and
Vertical Forces •••••••••• 27
• • • • • • • • • •
. . .. . . . . . .
2.2.1.2 Soil Failure Theories •••• 31
2.2.2 Soil Failure by Multiple Tines ••••••••••••• 42
2.2.2.1 Work on Lateral Interaction •••••••• 42
2.2.2.2 Shallow and Deep Tines Interaction. 43
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2.2.2.3 Combined Interaction •...•••••••.••• 44
2.3 Wetland Tillage for Paddy Cultivation •••••••••••• 46
2.3.1 Soil Condition for Rice Growth ••••••••••••• 46
2.3.2 Tillage Operations for Rice Crop .••.•.••••• 48
2.3.3 Soil Factors Influencing the Efficiency of
Puddling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
2.3.4 Measurement of Degree of Puddling .••••••••• 58
2.3.5 Puddling Efficiency of Different Tillage
Implements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
2.3.6 Water and Energy Requirement in Tillage
Operations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
.
,
3.0 Research Methodology.... • . • • • • • • • • • • • • • • • • • • • • • • • • • • • 73
4.0 Experimental Techniques and Apparatus •••••••••••••••• 79
4.1 Determination of Soil Physical and Mechanical
p~operties . . • • . • • . • • . . • • • . • . • • • • • . • • . • • • • • • • • • • • . 79
4.2 Clod wetting and Clod Drying Experiments ••••••••• 82
4.2.1 Sample Preparation......................... 82
4.2.2 Clod Drying Technique •••••••••••••••••••••• 82
4.2.3 Clod Wetting Technique ••••.••.•••.••••••••. 83
4.2.4 Measurement of Clod Volume and Porosity •••• 85
4.2.5 Measurement of Clod Moisture Profile ••••••• 85
4.2.6 Measurement of Clod Strength ••••••••••••••• 86
4.2.7 Measurement of Input Parameters Into Linear
Heat Flow Model.. • • • • • • • • • • • • • • • • • • • • • • • • • • 86
4.2.8 Measurement of Parameters for Jarvis and
Leeds-Harrison's Lateral Sorption Model •••• 90
4.3 Soil Tine Interaction Studies .................... 91
4.3.1 Description of Soil Tank ••••••••••••••••••• 91
4.3.2 Ins trumenta tion •••••••••••••••••••••••••••• 92
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4.3.2.1 Force Measuring Dynamometer.: •••••• 92
4.3.2.2 Signal Conditioning and Recording
Equipment ••••••••••••••••· ............. 92
4.3.2.3 Calibration of Dynamometer ••••••••• 93
4.3.4 Soil ••••••••••••••.•••••• : •••• 93
Preparation~
4.3.5 Tine Experiments............................. 94
4.3.6 Measurement of Soil Profile ••.••••••••••••• 95
4.3.7 Soil Disturbance Pattern ••••••••••••••••••• 96
4.3.7.1 Bead Tracer Technique •••••••••••••• 98
4.3.7.2 Talcum Slurry Technique •••••••••••• 99
4.4 Soil Puddling Experiments •••••••••••••••••••••• 102
~.
4.4.1 Design of a Laboratory Puddler............. 102
4.4.2 Instrumentation ............................ : 102
4.4.3 Soil Preparation .•••••••••••••• ; •• : ......... 102
4.4.4 Calibration of Wattmeter ••••••••••••••••••• 102
4.4.5 Aggregate Size Distribution Analysis: •••••• 103
4.4.6 Measurement of Soil Bulk Density ••••••••••• 103
5.0 Results and Discussion; ••••••••••••••••••••••••- •••• :. 105
5.1 Soil Physical and Mechanical properties •••••••••• 105
5.2 Clod Wetting and Clod Drying Studies .............. 105
5.2.1 Effect of Wetting on Clod Volume, Dry Bulk
Density and Moisture Content Profile Under
Two Stress Conditions •••••••••••••••••••••• 105
5.2.2 Effect of Wetting on Cone Depth ............. 112
5.2.3 Effect of Drying on Clod Volume, Dry Bulk
Density and Moisture Content Profile ••••••• 113
5.2.4 Input Parameters Into Soil Infiltration
Models..................................... 115
5.2.4.1 Linear Heat Flow Model ••••••••••••• 115
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5.2.4.2 Lateral Sorption Model ••••••••.•••• 117
5.3 Soil Tine Interaction Studies •••••••••••••••••••• 118
5.3.1 Calibration of Dynamometer ••••••••••••••••• 118
5.3.2 Results of Single Tine Experiments ••••••••• 119
5.3.2.1 Nature of Soil Disturbance ••••••••• 119
5.3.2.1.1 Visual Observation ••••••• 120
5.3.2.1.2 Soil Displacement Using
Bead Tracer Technique •••• 122
5.3.2.1.3 Soil Displacement.Using A
Glass Sided Tank ••••••••• · 124
5.3.2.1.4 Lateral Extent and Height
of Soil.Heave •••••••••••• 126
5.3.2.2 Draught Force ••••••••••••••••••••• 130
5.3.2.3 vertical Force •••••••••.•••••••••• 133
5.3.2.4 Magnitude and Direction of the
Resultant Force ••••••••••••.•.•••• 135
5.3.3 Results of Multiple Tine Studies ••••••••••• 136
5.3.3.1 Profile of Soil Disturbance •••••••• 136
5.3.3.2 Magnitude of the Total Draught and
vertical Force Components •••••••••• 138
5-.4 Soil Puddling Experiments........ • • • • • • • • • • • • • • • • 139
5.4.1 Calibration of wattmeter ••••••••••••••••••• 139
5.4.2 Aggregate Size Distribution of Puddled Soil 139
5.4.3 Bulk Density of Puddled Soil ••••••••••••••• 140
6.0 Force Prediction Models •••••••••••••••••••••••••••••• 144
6 • 1 Introduction..................................... 144
6.2 Single Tine Experiments •••••••••••••••••••••••••• 145
6.2.1 Soil Failure Mechanism ••••••••••••••••••••• 145
6.2.2 Development of the Force Prediction Models. 146