Effect of various dynamic loads on stress and strain behavior of a Norfolk sandy loam

Field traffic by heavy agricultural machinery can cause serve structural degradation of arable land. This may result in surface runoff, restricted availability of water, oxygen and nutrients to plant roots and therefore in reduced crop yields. In order to prevent these impacts and to develop appropriate counter-measures the complete compaction process must be understood. In this study the effect of increasing dynamic loads on the stress and strain relationship was examined using a stress state transducer (SST) attached to a displacement transducer system (DTS). Three different dynamic loads, ranging from 13.2 to 25.3 kN, were applied each by two passes on a firm sandy loam (Typic Kandiudults) at 10% wheel slip. During the first pass the calculated major principal (sigma(1)), mean normal (MNS) and octahedral shear stresses (OCTSS) increased significantly with increasing dynamic loads. For the second pass in contrast to these calculated stress values, except the major principal (sigma(1)), were not affected by the applied dynamic loads. While the vertical displacement of the transducer during the first pass was more than doubled with each dynamic load step, the soil volume element above the transducer was vertically deformed at a constant rate of 25%, independent of the dynamic load. Since no further vertical deformation of this soil volume element was induced by the second pass and additional vertical soil movement was detected, soil compaction is expected to progress to deeper soil layers as the dynamic load and the wheeling frequency increases. Thus the reduction of wheel loads and the avoidance of repeated wheeling events in one tire track may contribute to a sustainable land management of firm soils. (C) 1999 Elsevier Science B.V. All rights reserved.