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Construction of subsoilers and mode of operation.
Subsoilers are operated at a greater depth than the other conventional tillage implements, to break up the hard subsoil layers which result from compaction by traffic of farm equipment and tillage operations at the same shallow depth each season. They therefore have heavy shanks that can be operated at depths ranging between 450 to 750 mm or deeper (Srivastava, Goering and Rohrbach, 1996).
As shown in figure 1.1, a typical subsoiler is made up of a shank and a foot with a share. The foot and the share do all the work of cutting the soil and lifting it over its entire width. According to McKyes (1985), the foot acts as though it was a flat blade extending all the way to the soil surface at an angle equal to its rake angle (α).
To improve the tillage effectiveness and efficiency of subsoilers, wings or blades are often added to the foot (Trousse and Humbert, 1959) thus increasing the critical depth. At the same time, variations of the conventional subsoiler aimed at reducing their drawbar power requirements, have been developed over the years. Some of the interventions in subsoiler designs include straight or bent-legged, triplex and parabolic shaped shanks (Harrison, 1990).
In this study, straight shanks with narrow blades, but without wings were used. In most cases, straight shanks are angled with a slight rearward incline to reduce draft forces. Soil disturbance from straight shanks is symmetric with equal amounts of soil being disturbed on either side of the shank. The force system in such a tillage process, where soil failure is symmetrical, consists of two mutually perpendicular force components, a horizontal (H) and a vertical (V) force, and a moment (M) in the plane of these two forces. The lateral forces and lateral moments are zero in this kind of symmetrical soil failure.
CHAPTER I. INTRODUCTION
1.1 Background
1.2 Construction of subsoilers and mode of operation
CHAPTER II LITERATURE REVIEW
2.1 Soil compaction .
2.2 Theory of soil-failure in passive tillage
2.2.1 Effects of tillage tool-operating width
2.3 Power requirements for soil engaging tools
2.4 Development of soil failure profile models
2.4.1 Analytical approach
2.4.2 Numerical approach
2.5 Conclusions from the reviewed literature
2.6 Justification for conducting this study
2.7 Hypotheses
2.8 Objectives
2.9 Chosen procedure and justification
CHAPTER III DEVELOPMENT OF THE MATHEMATICAL FORCE MODEL FOR THE RSS
3.1 Center soil-failure wedge
3.2 Side soil-failure wedge
3.3 Determination of the total disturbed soil-volume and forces
CHAPTER IV INSTRUMENTATION AND CALIBRATION
4.1 Instrumentation
4.2 Calibration of the load-cells.
4.3 Calibration of the dynamometer
CHAPTER V RESEARCH METHODOLOGY
CHAPTER VI RESULTS AND DISCUSSION
CHAPTER VII SUMMARY, CONCLUSIONS AND RECOMMENDATIONS.
