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ARS Home » Midwest Area » Columbia, Missouri » Cropping Systems and Water Quality Research » Research » Publications at this Location » Publication #150338
Title: MODELING SOIL FAILURE CAUSED BY PRISMATIC AND CONICAL TOOLS

Author
item CHUNG, SUN-OK - U OF MO
item Sudduth, Kenneth - Ken

Submitted to: American Society of Agricultural Engineers Meetings Papers
Publication Type: Other
Publication Acceptance Date: 7/31/2003
Publication Date: 7/31/2003
Citation: CHUNG, S., SUDDUTH, K.A. 2003. MODELING SOIL FAILURE CAUSED BY PRISMATIC AND CONICAL TOOLS [CD-ROM]. AMERICAN SOCIETY OF AGRICULTURAL ENGINEERS. PAPER NO. 03-1028.

Interpretive Summary: Precision agriculture aims to minimize costs and environmental damage caused by agricultural activities and to maximize crop yield and benefits based on information collected at within-field locations. One parameter that can vary considerably within fields and also significantly affect crop yields is soil strength or compaction. To efficiently quantify compaction, there is a need for a soil strength sensor that can take measurements continuously while traveling across the field. This paper reports on a portion of our research to develop such a sensor. We developed mathematical models to describe the interaction of the soil with two types of cutting tools. The first was a vertically operating cone penetrometer, the standard device currently used to quantify soil compaction. The second was a horizontally operating prismatic cutter, the candidate design for our prototype soil strength sensor. We applied the prismatic cutter model to select design parameters of the prototype sensor, including overall dimensions, location, load rating and spacing of sensing elements. Both models were similar mathematically, with the major differences due to the differences in geometry between the two cutting tools. This similarity holds promise for being able to interpret data from the prototype sensor using approaches already developed for cone penetrometer data. The results of this research will benefit other researchers working in the field, by providing them with mathematical models to help understand sensor behavior and to aid in interpreting test data.

Technical Abstract: Soil strength, or mechanical resistance of a soil to failure, has been widely used to estimate the degree of soil compaction. Conventional measurements with cone penetrometers are laborious; therefore, we are working to develop an on-the-go soil strength profile sensor to collect data dense enough to show the spatial variability of soil strength in an efficient manner. Because soil failure involves complex interaction of many variables, determining design parameters of a soil strength sensor and interpreting test results would be improved with a theoretical understanding of the soil failure process. Mathematical models to estimate the force required to penetrate (cut and displace) soil with a prismatic cutter traveling horizontally and a cone penetrometer traveling vertically were developed based on the passive earth pressure theory. Both models were expressed as additive forms of density, cohesion, and adhesion components of the soil, with each effect multiplied by a corresponding dimensionless number. Graphic charts of dimensionless numbers were developed to investigate the behavior of each strength component at various values of soil internal friction angle, soil-metal friction angle, and cutting angle of the tool. The model for the prismatic cutter was validated with experimental results, and then used in simulation to optimize design parameters of the sensor, such as dimensions, and locations and spacing of sensing elements.