Impact of sample dimensions, soil-cylinder wall friction and elastic properties of soil on stress field and bulk density in uniaxial compression tests

Compressive properties of arable and forest soils are typically derived from data obtained in uniaxial confined compression tests. However, the stress field, final state of compression and thus compressive properties derived from such tests are dependent on sample dimensions, soil-cylinder wall friction and soil material properties. In this study, we analysed the stress field and bulk density distribution within a cylindrical soil sample under uniaxial compression, and how these are affected by sample dimension, soil-cylinder wall friction and elastic properties of soil. For this, we modelled a uniaxial compression test using the finite element method (FEM) and performed simulations for a range of sample diameter to height ratios (D/h), different values of soil-wall friction coefficient (mu) and different soil elastic properties (Young's modulus and Poisson's ratio). We use experimental data to validate the findings. The results showed a high impact of soil-cylinder wall friction on the stress field within the sample. This resulted in stress concentration at the top of sample edges (walls) and decreasing stresses at the bottom of the sample. However, the relative impact of soil-wall friction on sample average behaviour decreased with increasing D/h. These results suggest that the effect of soil-wall friction on sample-average bulk density cannot be neglected unless D/h > 8. Correction of bulk density for mu and D/h could be a practical way to compare data obtained in laboratories using different sample sizes.