Shaft Friction of an ASABE Standard Soil Cone Penetrometer

Abstract

Listen

Translate article

<abstract><title><italic>Abstract.</italic></title> To ensure penetration results that are comparable under various experimental conditions, cone penetrometers specified by ASABE Standards have been suggested for many years. Elastic-plastic properties are typical of most agricultural materials, so the material being penetrated by a cone penetrometer may contact the penetrometer shaft, and friction on the shaft may affect the penetration force data. Development of a method for quantifying this friction force is expected to improve the accuracy of cone penetrometer data. The objectives of this study were: (1) to evaluate a method for determining friction force on the shaft of a cone penetrometer while penetrating sand and clay soils packed in a specific cylinder, (2) to verify the penetration friction component (PFC) that may significantly influence penetration resistance (PR) measurements for various densities of chopped maize, and (3) to assess the effectiveness of a proposed filter method for adjusting friction on the penetrometer shaft. With these intentions, we embedded strain gauges into an ASABE Standard small cone. The tip was free from the shaft friction, so the output of this sensor was used as a reference in this study. We found the ASABE Standard small cone suitable for a broad range of soil textures, as little PFC was observed from the sand or the clay soil samples. However, considerable friction from penetrating chopped maize was observed at three levels of packed density using the cylinder method. In this situation, with the reference of the sensor output inside the tip, a pair of coefficients (C₁ = 2329, C₂ = 2120) were optimized to filter the PFC out of the PR measurement. The adjusted data agreed well with those of the reference sensor (R² = 0.968; RMSE = 6.521 N). Thus, ASABE Standard penetrometers can also be used for silage materials without mechanical modification.