TECHNIQUES FOR MEASURING CHANGES IN THE PACKING STATE AND CONE RESISTANCE OF SOIL AFTER THE PASSAGE OF WHEELS AND TRACKS

Methods are described for measuring the changes in the horizontal and vertical distribution of packing state and cone resistance following the passage of wheels and tracks over prepared beds of soil. A gamma-ray transmission system was employed with automatically controlled scanning in a 2 × 2 cm grid in soil sections of 1.08 m length by 0.3 m depth, using a scintillator/photomultiplier detector assembly with stabilized pulse-height analysis and magnetic tape recording. Changes in cone resistance were measured in a 2 cm (vertical) by JO cm (horizontal) grid in a section 1.4 m length by 0.5 m depth using an electrically driven penetrometer with load and displacement simultaneously recorded on an XY plotter and magnetic tape. Results were analysed and displayed graphically by computer with packing state expressed by a number of optional properties (dry bulk density, total porosity, air-filled porosity, void ratio, or specific volume). Pronounced differences in packing state and soil strength were observed as a result of the passage of a two-wheel-drive tractor, with and without cage wheels, and a crawler tractor. Adding a cage wheel decreased slightly the compaction below the rubber tyre, but formed a partially compacted zone below the cage wheel. Increases of dry bulk density and soil strength were recorded below the crawler track but the values for these properties did not reach the maximum values found below the rubber tyre.