INVESTIGATION OF CLOSE-RANGE PHOTOGRAMMETRY & SOIL STRENGTH TESTING FOR THE EVALUATION OF SOIL COMPACTION

A major cause of reduced crop productivity worldwide is soil compaction, which has been increasing due to intensive farm practices along with increasing farm equipment weights. Tractor tire manufactures are designing and currently producing tires to minimize soil compaction. Soil-tire interaction, however, is complex and difficult to quantify. To assess the soil compaction, three methods were used in this dissertation: tactile sensor pads, photogrammetry and cone penetrometer strength testing. Two full scale tractor tires were tested using a servo-hydraulic loading system to produce tire ruts under known loads and time durations to determine the difference in soil compaction caused by tires. Tactile pressure sensors were used to measure the ground pressure from tractor tire loads in a laboratory setting. Two full-size tractor tires were tested; a traditional tractor tire W800/70R38 and a recently developed low-aspect ratio tire IF800/55R46 which has been developed to reduce tractor ground pressures and minimize soil compaction. To capture the entire tire footprint in soil, four 5400N tactile pressure sensors from Tekscan were placed at the bottom of a soil bin in the laboratory. The contact area, average ground pressure and peak ground pressure due to static tractor tire loading on loose sand were successfully recorded by the tactile pressure sensors. Close-range digital photogrammetry was also utilized to construct the 3D models of the tire footprint. These models were then analyzed to obtain the tire footprint depth, area and volume. Laboratory experiments were conducted to compare the tire footprint and cone index of two tractor tires, i.e., the IF800/55R46 and W800/70R38 tires. Photogrammetry was utilized to produce 3D model of the tire rut in soil and a standard ASABE cone penetrometer was used to provide a relative measure of soil compaction by measuring the cone index (CI) of soil. Our experiments showed the highest compaction is observed at the center of the tire footprint. This is seen as the deepest rut from the photogrammetry models and largest CI values from the cone penetration tests. Based on our static vertical tire loading tests in the laboratory, there appears to be minimal difference in the CI and rut depth and volume of the two tires tested. These results concur with our previous experiments where similar normalized contact area were recorded when the ground pressure in soil was measured using tactile pressure sensors for the two tested tires. The photogrammetry technique was also proposed as a new method of obtaining the volume of the test holes in field density tests. Laboratory and field experiments were developed to investigate the capability of the photogrammetry technique in providing the volume of the test holes in soil. The photogrammetry technique was also utilized to obtain the volume of the test holes in field density tests in a sand field and provided the volume of the test holes with relative errors of less than 6% and an average error of 0.11%. Our experiments also revealed the importance of the calibration procedure in sand cone density method