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

Field traffic by heavy agricultural machinery can cause serve structural de gradation of arable land. This may result in surface runoff, restricted ava ilability of water, oxygen and nutrients to plant roots and therefore in re duced crop yields. In order to prevent these impacts and to develop appropr iate counter-measures the complete compaction process must be understood. I n this study the effect of increasing dynamic loads on the stress and strai n relationship was examined using a stress state transducer (SST) attached to a displacement transducer system (DTS). Three different dynamic loads, r anging from 13.2 to 25.3 kN, were applied each by two passes on a firm sand y loam (Typic Kandiudults) at 10% wheel slip. During the first pass the cal culated 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 wa s more than doubled with each dynamic load step, the soil volume element ab ove the transducer was vertically deformed at a constant rate of 25%, indep endent of the dynamic load. Since no further vertical deformation of this s oil volume element was induced by the second pass and additional vertical s oil movement was detected, soil compaction is expected to progress to deepe r soil layers as the dynamic load and the wheeling frequency increases. Thu s the reduction of wheel loads and the avoidance of repeated wheeling event s in one tire track may contribute to a sustainable land management of firm soils. (C) 1999 Elsevier Science B.V. All rights reserved.