Width Prediction of a Side Circular Crescent Failed by a Tillage Tool in a Sandy Clay Loam


  • Kasisira Lukoda Levi
  • duPlessis Ronnie


Some of the mathematical force models employing limit equilibrium analysis are based on the soil-volume tilled to predict the draft requirements of a tillage tool. At the same time, such models require a preliminary assumption of the soil failure pattern ahead of the tool. It is imperative therefore to accurately determine the dimensions of the idealized soil-failure model to ensure accurate prediction of the soil-volume tilled and thus the tillage-tool draft requirements.


Among the commonly idealized models, is the model that divides the soil failure ahead of a simple tillage tool into a center wedge and a side circular crescent on each side of the tool. However, the available model for determining the maximum width of the side circular crescent was found to over predict its size. This was mainly due to being insensitive to soil water content. A study was therefore carried out to develop a model expressing the maximum width of the failed side circular crescent in terms of soil water content. Tests were conducted under field conditions in a sandy clay loam soil using conventional subsoilers in a tandem configuration at an operating depth of 600 mm


Unlike the available model, the results showed that the proposed model adequately predicted the maximum width of the failed side circular crescent resulting in satisfactory prediction of the tilled soil volume. This would lead to limit equilibrium analysis based models to sufficiently predict draft requirements of tillage tools. In conclusion it was observed that the size of a failed soil-wedge is more sensitive to soil water content than the geometric dimensions of a tillage tool.


Key worlds: Side circular crescent, failed soil-wedge, model, maximum width, tillage tool

Author Biographies

Kasisira Lukoda Levi

Senior Lecturer

Dept of Agrcultural Engineering, Makerere University, Kampala-UGANDA


duPlessis Ronnie


Dept of Civil & Biosystems Engineering, University of Pretoria, Pretoria-SOUTH AFRICA






III-Equipment Engineering for Plant Production