SOIL STRESS-DISTRIBUTION UNDER LUGGED TIRES

The spatial distribution of stress under a lugged tire was investigate d by model calculations and a field experiment. The stress model used is based on the analytical solution of the linear elastic case and was in satisfactory agreement with the field experiment. The spatial dist ribution of stress and resulting deformation is considered from severa l viewpoints. As expected, a tire resting only on its lugs introduces a large heterogeneity in the stress state near the soil surface, leadi ng to deviations of the vertical stress at 5 cm depth of up to 100%. A dditional deviations in the model are an artefact of the coarse resolu tion of the surface load. When calculated stress was related to Mohr-C oulomb theory, failure zones under the lugs occurred, unlike with a sm ooth tire. A driving force, which acts horizontally on the surface, wi ll enhance shearing deformation and failure by introducing tensile str esses in front of the tire. Generally the heterogeneity introduced at the surface decreased with depth. To relate stress occurring in the fi eld to laboratory measurements, the principal stresses and their time dependence were calculated for a commonly-used sample size. Since stre ss and strain states that can be obtained in laboratory tests are rest ricted, the model may help the choice of the proper test and loading p aths for studying deformation behavior of a soil under a moving tire.