Mehari Z. Tekeste

ACOUSTIC COMPACTION LAYER DETECTION

The ASAE standardized tool to detect the depth and strength of compaction layers in the field is the cone penetrometer. Since this method is point-to-point, researchers have experimented with on-the-fly alternatives that can be used as, or in combination with, a standard tillage tool. On-the-fly compaction layer sensing also enables adaptive tillage, where the soil is only tilled as deep as necessary, which can lead to significant energy savings and erosion reduction. Wedged tips, strain gauges mounted on a deflecting tine, air bubbles pushed into the soil, as well as ground-penetrating radar have been tested for this purpose. In this research, passive acoustics was used to detect the compaction layer by recording the sound of a cone being drawn through the soil. The premise was that a more compacted layer should cause higher sound levels, which might reveal the depth and strength of the compaction layer. Two experiments were conducted in the soil bins of the USDA-ARS National Soil Dynamics Laboratory in Auburn, Alabama. First, constant-depth tests (15 and 30 cm) at three compaction levels (0.72, 2.8, and 3.6 MPa) revealed the relationship of sound amplitude with depth and compaction. Second, to test the detection capability, the cone was gradually inserted in the soil, passing through an artificial compaction layer. A windowed, short-time Fourier transform (STFT) analysis showed that the compaction layer is detectable since the sound amplitude was positively related to depth and compaction levels, but only in the highest frequency range of the spectrum. This led to the conjecture that the soil-cone interface acts as a low-pass filtering mechanism, where the cutoff frequency becomes higher in the compaction layer due to a more intimate contact between sensor and soil.

A PORTABLE TILLAGE PROFILER FOR MEASURING SUBSOILING DISRUPTION

A portable tillage profiler (PTP) was constructed using a laser distance sensor, a linear actuator, a portable PC, and a lightweight aluminum frame that can quickly and accurately measure aboveground and belowground soil disruption caused by tillage. A laboratory experiment was conducted that determined that soil color did not detrimentally affect the PTP, with expected vertical errors of 2.3 mm and horizontal errors of 0.6 mm being found. However, when pure white and black objects were examined, the errors increased to 4.2 mm vertically and 11 mm horizontally. This maximum error was established when attempting to measure the height and width of a wedge, which had a sharpened edge pointing vertically upward. The PTP was used in the National Soil Dynamics Laboratory soil bins to measure both aboveground and belowground soil disruption caused by two subsoiler shanks. The PTP gave results that enabled differences between the aboveground disruptions caused by each subsoiler to be statistically established.

Finite Element Analysis of Cone Penetration in Soil for Prediction of Hardpan Location

An accurate determination of soil hardpan location is important for maximum precision tillage performance. Cone penetrometers are often used to locate hardpans in soils. This determination in layered soils is more complex due to the complexity of soil reaction to cone penetration. An axisymmetric finite element (FE) model was developed to simulate cone penetration for the prediction of the hardpan location in a layered Norfolk sandy loam soil. The soil was considered as a non-linear elastic-plastic material, and it was modeled using a Drucker-Prager model with the Hardening option in ABAQUS, a commercially available FE package. ABAQUS/Explicit was used to simulate soil-cone contact pair interaction. The results showed that the FE model captured the penetration resistance trend with two deflection points indicating the start of the hardpan and the peak cone penetration resistance. The FE-predicted results showed the hardpan at a depth of 7.29 cm compared to 11.08 cm from cone penetration tests. Soil moisture, bulk density, and cone surface conditions significantly affected the predicted and experimental results. The simulation also showed soil deformation zones about 3 times the diameter of the cone that developed around the advancing cone.

Effect of Soil Moisture, Soil Density, and Cone Penetrometer Material on Finite Element Prediction of Soil Hardpan Depth

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 depth (8.62 cm) was 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.

Acoustic Compaction Layer Detection

In order to study the dynamics of variation in three-dimensional soil surface caused by water erosion, a new system equipped with an automated photogrammetry was developed in our laboratory. The system consists of two digital cameras, a rain simulator with a twelve meters high tower, and a set of computer image analysis program of three-dimensional algorithm. The system was tested using soil boxes where soils were packed with a 10o slope and under conditions of (1) rainfall, (2) surface water flow, (3) the combination of both rainfall and surface flows and (4) intermittent surface flow. The measurement error of the system was evaluated using standard deviation (SD) between the depth of soil erosion due to measurement and analysis. The average SD was 2.8 mm for a clay soil and 2.0 mm for a sandy loam soil under rainfall conditions. The SD was reduced to 1.9 mm in a heavy clay soil under intermittent surface flow condition. The measuring error was affected by the light halation, as well as soil color, amount of water stored on the soil surface.

A Portable Tillage Profiler for Measuring Subsoiling Effectiveness

A portable tillage profiler (PTP) was constructed using a laser distance sensor, a linear actuator, a portable pc, and a lightweight aluminum frame that can quickly and accurately measure above- and belowground soil disruption caused by tillage. A laboratory experiment was conducted that determined that soil color did not detrimentally affect the PTP with expected vertical errors of 2.3 mm and horizontal errors of 0.6 mm being found. However, when pure white and black objects were examined, the errors increased to 4.2 mm vertically and 11 mm horizontally. This maximum error was established when attempting to measure the height and width of a wedge, which had a sharpened edge pointing vertically upward. The PTP was used in the NSDL soil bins to measure both above- and belowground soil disruption caused by two subsoiler shanks. The PTP gave results that enabled differences between the aboveground disruption caused by each subsoiler to be statistically established.