Submitted to: ASAE Annual International Meeting
Publication Type: Other
Publication Acceptance Date: 7/17/2005
Publication Date: 7/17/2005
Citation: Tekeste, M.Z., Raper, R.L., Tollner, E.W., Way, T.R. 2005. Effect of soil moisture, soil density, and cone penetrometer material on finite element prediction of soil hardpan depth. ASAE Annual International Meeting. Paper No. 051164. Interpretive Summary: Soil cone penetrometer is a widely used instrument to measure soil compaction, however, its ability to sense root-restricting profiles may be affected by soil moisture variation. A computer model was used to investigate the cone penetrometer's ability to sense this root-restricting layer due to varying soil parameters (soil moisture and bulk density) and cone materials (Stainless steel, Teflon, and Teflon coated stainless steel). Computer models and experimental tests showed that under dry soil moisture conditions and relatively high soil-cone friction (e.g. Stainless steel) the root-restricting layer was predicted at a shallower depth. From this study, it can be suggested that interpretations of cone penetrometer data to predict the depth of soil hardpans for precision tillage should consider the soil moisture contents and soil-cone friction properties.
Technical Abstract: An accurate soil hardpan determination is important for maximum precision tillage performance. Soil cone penetrometer data are often analyzed to predict soil hardpan depths. The prediction in layered soils may be limited due to the complexity of soil reaction to cone penetration. An axisymmetric finite element (FE) model was developed to investigate soil hardpan predictions and soil deformation failures on layered Norfolk sandy loam soil. The soil was considered as a non-linear elastic-plastic material modeled using a constitutive relationship from Drucker-Prager model with the Hardening option in ABAQUS, a commercially available FE package. ABAQUS/Explicit was used to solve the simulation of soil-cone contact pair interaction using a frictional property. The results showed that the FE model captured the soil cone penetration trend in layered soil with two deflection points indicating the start of the hardpan and the peak cone penetration resistance. The FE model predicted hardpan depths (8.62 cm) were smaller than the cone penetrometer predicted depth (11.03 cm). Soil moisture, bulk density and cone material significantly affected the FE and cone penetrometer predicted soil hardpan depths. The simulation also showed soil deformation zones about 3 times the diameter of the cone developed around the advancing cone.