E. McKyes

The cutting of soil by narrow blades

Abstract The available models for predicting the forces acting on a narrow soil cutting blade have required separate measurements of the shape of the three-dimensional soil failure pattern ahead of the blade. It is proposed that a three-dimensional model consisting of straight line failure patterns in the soil can be used to predict both the draft forces and the volume of soil disturbed in front of a narrow blade. Limit equilibrium mechanics equations are written for the soil wedges in terms of an unknown angle of the failure zone and the theoretical draft force is minimized with respect to this angle. Force factors are thus found which are of the type to fit Reeces general earthmoving equation, but which vary with the width to depth ratio of the blade as well as with the rake angle of the blade and the friction angle of the soil. In addition the approximate geometry of the three-dimensional failure pattern in the soil is predicted for varying blade shapes and soil strengths. This allows the design of simple tools on the basis of their draft force requirements and their soil cutting efficiency. The draft force predictions and failure geometry calculations are shown to have considerable verification by experimental results.

Peatmoss Effect on the Physical and Hydraulic Characteristics of Compacted Soils

ABSTRACT MEASUREMENTS of the water retention characteristics, saturated hydraulic conducivity and the penetration resistance were made on three soil types having varying organic matter contents and different amount of compaction effort. Compaction changes the ability of the soils to hold moisture, increases penetration resistance and decreases the available water capacity and saturated hydraulic conductivity of the soils. On the other hand, organic matter generally increases the ability of the soils to hold moisture, expands the available water capacity, increases the saturated conductivity and decreases the penetraiton resistance of compacted soils.

Prediction of clay soil compaction

Abstract Field measurements were made of soil density and moisture patterns under different vehicle tire paths with varying external pressures and number of passes. In addition, laboratory index tests were performed to determine the compaction behaviour of the same soil. Using these results, a prediction equation of dry density in terms of applied pressure and moisture content was obtained for the clay soil. A previously developed equation for sandy soil was modified for the complete range of moisture contents encountered. Estimation of shear strength for the clay soil was made using plastic and liquid limits.

Subsoil compaction in a clay soil. I. Cumulative effects

Abstract A 3-year investigation was carried out on the effect of annual compaction by 10- and 20-t axle −1 loads applied at 2 soil moisture contents on bulk densities and on corn ( Zea mays L.) yields in a clay soil. Maximum bulk densities, and the depth at which they occurred, increased with each annual loading. Only the 20-t axle −1 loading increased soil density when compacting under dry conditions. However, both loading levels led to increases in density when applied under relatively wet conditions. Under the latter conditions, moldboard plowing and overwintering did not fully relieve topsoil compaction. Trends in crop responses to compaction were similar to those of soil bulk density. However, corn yield reductions were much more pronounced than were changes in soil structure. Differences in yields between the effects of each loading level increased with annual compaction.

Shear Strength Prediction of Compacted Soils with Varying Added Organic Matter Contents

T HE shear strength of compacted soils is affected by many factors including soil density, overburden pressure, moisture content, energy applied for compaction and soil type. Measurements were made of the shear strength of three soil textures, varying in organic matter contents and subjected to three levels of compaction energy. Soil compaction increased the shear strength of the soils irrespective of moisture content, while organic matter incorporation decreased their shear strength. Based on the liquid limit, the pressure applied for compaction and the water content, a method for predicting the shear strength of soils was developed. The estimated shear strength using the model was in good agreement with the measured values.

Effect of design parameters of flat tillage tools on loosening of a clay soil

Abstract Very little research has been done to investigate soil loosening as a function of the geometry of the tillage tool and of the original soil properties and moisture content. A field experiment was conducted to observe the effects of the geometric parameters of flat tillage tools on their draft, cutting efficiency and loosening of a moist clay soil. The test tool variables included rake angles to the horizontal of 30, 60 and 90°, widths of 75 and 150 mm and depths of operation of 100, 150 and 200 mm. Measurements were taken of draft, disturbed soil cross sectional profiles and the initial area of soil disturbed by the tools. The resulting draft requirement increased with width, depth and rake angle of the tool. The cross sectional area of soil disturbed did not change appreciably with rake angle, but the significant increase in draft with angle resulted in markedly diminished soil cutting efficiency (area divided by draft). The degree of soil loosening was generally smaller at a rake angle of 60° than at 30 or 90°, and tended to be higher at greater depths of operation. In addition, a larger depth to width ratio generally increased the degree of loosening. Results for the soil studied indicate that the best implement design for low draft, high cutting efficiency and superior soil loosening should have a rake angle of about 30° and should be fairly narrow with a depth to width ratio of 2 or more.

Prediction and field measurements of tillage tool draft forces and efficiency in cohesive soils

Abstract Field experiments were conducted in clay and sandy clay loam soils using flat tillage blades of varying width, depth and rake angle. Measured quantities of draft force and disturbed soil areas for the different test conditions were compared to those predicted by a model of soil wedge failure in front of narrow blades, with reasonable agreement. Both the specific draft force per unit soil area and the degree of soil loosening were observed to increase with the relative narrowness of the tillage blades and with the rake angle, as predicted by the model.

The Relationship Between Machinery Traffic and Corn Yield Reductions in Successive Years

ABSTRACT TO understand and assess damage to corn production by soil compaction generated by vehicular traffic, a randomized complete-block design was selected to lay out plots to comprise treatments of 1, 5, 10 and 15 passes with contact pressures of 62, 41 and 31 kPa and a control of zero traffic. These experiments were performed in two successive years in a Ste. Rosalie clay soil to incorporate the effect of weather conditions. Agronomical treatments were kept the same for all the plots. During the 1976 growing season, a yield loss of 40 to 50 percent was obtained in plots with higher contact pressures and multiple passes. The experiment in 1977 showed losses up to 30 percent, the highest yields occurring in the moderately compacted plots. Models of plant output parameters in terms of vehicular traffic were com-pared.

Prediction of Soil Compaction Due to Off-Road Vehicle Traffic

ABSTRACT SIMULTANEOUS field and iab-*J) oratory compaction data were examined in order to determine the prediction possibilities. Several existing theories were also considered for comparison. An equation repre-senting dry density in terms of applied pressure and moisture content was used to describe the field and labor-atory data. The pressure applica-tion on the agricultural soil varied from near 0 to 1.62 kg/cm2, and field data obtained at various moisture contents provided necessary informa-tion for arriving at the laboratory index test methods. The pattern of real compaction under tire loads was found to compare well with the standard Proctor compaction test. Results of such attempts are very useful for off-road machninery de-signers and farmers.

Characterization of cohesion, friction and sensitivity of two hardsetting soils from Zimbabwe

Abstract Hardsetting soils are defined as those which develop very high strength with little observable structure when they dry, but lose much of their strength when wet. Sandy loam soils (haplic lixisol) which showed typical hardsetting behaviour in the field were identified in a small-scale farming are in Zimbabwe. They were too hard to cultivate when dry, and produced a cloudy structure when plowed by a tractor in a slightly moist state. Samples of two sandy loam topsoils were collected, prepared at different water contents varying from saturated to field-dry and tested for stress-deformation and shear strength behavior in a direct shear box. For both soils at water contents above 10 g 100 g−1, the stress-deformation curves are of the plastic material type with continually increasing shear stress with deformation. At water contents less than 10 g 100 g−1, curves associated with more brittle material behavior resulted, with a peak shear stress reached at 3–4 mm deformation followed by a considerable loss in strength. At nearly all of the water contents, the angle of friction was 34–37° for both soils, but cohesion changed from nearly zero at saturation to well over 100 kPa in the field-dry state. The contribution of matric tension alone to soil cohesion is more than enough to account for the observed increases in strength on soil drying, and the potential role of soluble silicate cementing agents does not appear to be a factor in the case of these two soils.