Simulating stress-sinkage under a plate sinkage test using a viscoelastic 2D axisymmetric finite element soil model

Understanding the compressive behavior of soils is essential to predict the alterations that might occur in soil structure when submitted to stress caused by agricultural machinery. Soil compression curve has been used to understand the process of compression. Pre-compaction stress (sigma(pc)) and compression index are important parameters which can be obtained from compression curve and are used in evaluating soil load support capacity and its susceptibility to compaction, respectively. Plate sinkage test (PST) could be used in determining soil compressive parameters (sigma(pc); deformability coefficient, C-D). In this research, the stress-sinkage behavior of a silty clay loam soil treated with long-term incorporation of sewage sludge (SS) with four application rates (0, 25, 50 and 100 t ha(-1)) was simulated using the finite element method (FEM). The soil was modeled as a two-dimensional axisymmetric structure using ANSYS. The soil material behavior was assumed as a linear viscoelastic material. Soil shear relaxation kernel function was obtained from the results of confined compression relaxation test and direct shear box test using well-defined relations between elastic properties. The FEM model was verified against the experimental results obtained using the PST on repacked remolded soil samples. The FEM model successfully simulated the trend of soil stress-vs.-sinkage under PST. The sigma(pc), values derived from the experimental data over-estimated the applied preload, on average, by 69%; whereas excellent agreement between the FEM simulated values and the preload was demonstrated for the SS amended soils. In consolidation theory, the sigma(pc) indicates the maximum effective stress to which the soil has been subjected; however, the sigma(pc) values driven from the experimental results were obtained by assuming that the total applied stresses were equal to effective stresses. Therefore, the sigma(pc) values obtained from FEM simulation data and the experimental data could be considered as effective and apparent sigma(pc), respectively. The results show that the simulated sigma(pc) linearly changes with both soil Young's modulus and Poisson's ratio, whereas the C-D was independent of both. (C) 2011 Elsevier B.V. All rights reserved.