Abstract
Soil characteristics have a fundamental influence on the motion of vehicles traversing terrain. The principal mechanical parameters of soils are moisture content, loadbearing capacity, shear strength and soil settlement, which in turn influences soil density. These characteristics take effect on the vehicle's motion through the shear and normal loads which develop between the soil and the tyre. Moisture content assists the travel of the vehicle in some soils assists and hinders it in others. The level of settlement of the soil crucially influences its load-bearing capacity. Newly-tilled soil has a poor load-bearing capacity, and is therefore prone to large vertical deformations.
Measurements were performed on a particular loam soil to determine the changes of internal friction with moisture content; cohesion with settlement and cone index; and cone index with settlement.
The tests were performed on soil which had settled after various tillage operations--. The measurements were made in February, March, April, June, October and December, and thus spanned a whole year. To systemize the measurement series and render them repeatable, twelve test points were marked out on the test area. These points were fixed using a GPS device to ensure successive measurements were made at precisely the same places. Evaluation of the test results show that the internal friction of the soil decreased with increasing moisture content. This agrees with other findings in the literature, and is due to the lubricating effect of the water. Cohesion and cone index increased with settlement, a dependence which indicates that it is insufficient to measure the variation of cohesion and cone index as a function of moisture content alone.
Since the effects of moisture content, settlement, cohesion and cone index on the soil-tyre interaction have not yet been sufficiently established, such measurements are an important contribution to a deeper understanding of the mechanical parameters of soils.
Keywords: terramechanics, terrain characterization, soil-mechanical parameters, soil measurement, loam soil