Evaluating DEM results with FEM perspectives of load : soil interaction

Keywords: Load - soil interaction, soil structure, soil mechanical properties, FEM (Finite Element Method), Plaxis (Finite Element Code), granular particles, shear stress, DEM (Distinct Element Method), micromechanics of deformation, interparticle friction coefficientFor researchers concerned with soil compaction, soil structure is assessed by indirect measurement of parameters related to soil mechanical properties. In this study the mechanical properties of soil are investigated for the dynamic load - soil interaction of tyre - soil systems, tool penetration, shearing and soil cutting by a pendulum type machine. The methods selected for analyses are the Finite Element Method (FEM) and the Distinct Element Method (DEM). The dynamic module of Plaxis (a special purpose finite element program released in 2000), is more advanced than the previous version of Plaxis. In Plaxis calculations, the Mohr - Coulomb model is selected for deformable soil and theCam- Clay type model is selected for compactable soil properties. Results of these model studies are presented briefly for the above load - soil interactions. Although the dynamic module of Plaxis performs better, the problems of analysing the discontinuous properties of soil such as shearing (sliding), cutting and cracking (fracturing) still remain unsolved due to the continuous nature of the medium.In such cases, representing soil as a discontinuous medium as in DEM is more realistic.In DEM, soil is an assembly of discrete particles (discontinuous medium) with the possibility of cyclic contact and failure, by updating contact interactions throughout the simulation. The appropriate models selected are: the original DEM for cohesionless particles and the modified Kyoto DEM in which the adhesion force between particles is considered.The simulation results show that the mechanical properties of the particles are dependent on the micromechanics of deformation. Shear stress and failure appear largely to be influenced by interparticle sliding and rolling. Sliding contacts are always greater for the low values of interparticle friction coefficient. If this value is sufficiently high, especially for coarse and medium granular particles sliding will be very low and rolling of particles dominates the system which results in low shear stress values. Moreover the contact stiffness and the particle size have an important influence on the deformation mechanisms. For instance, for coarse and medium granular particles, soft stiffness shows compaction whereas hard stiffness shows dilatancy during the shearing process. In the simulation of soil cutting by a pendulum type machine adhesive particles are displaced more or less together by forming soil clods. The deformation behaviour of particles and the crack propagation during the cutting process are significantly affected by the adhesion coefficient between particles, the interparticle friction coefficient and the particle size.In our simulation, parameter analyses were performed by varying the most relevant model inputs. Normal and tangential stiffness between particles, interparticle friction coefficient, adhesion coefficient between particles and particle size turned out to be the most influential input parameters. Finally results from this simulation are qualitatively compared with those of Plaxis and also some similar laboratory test results reviewed from literature are selected for benchmarking. By evaluating the model results using comparisons, the potential capability of the DEM model on showing the actual soil properties during the above load - soil interaction could be approved.

Bibliographic Details

Main Author:	Tadesse, D.
Other Authors:	Perdok, U.D.
Format:	Doctoral thesis biblioteca
Language:	English
Subjects:	dynamic loads, finite element analysis, particles, simulation models, soil compaction, soil mechanics, soil properties, soil structure, bodemeigenschappen, bodemstructuur, bodemverdichting, deeltjes, dynamische belasting, eindige-elementenmethode, grondmechanica, simulatiemodellen,
Online Access:	https://research.wur.nl/en/publications/evaluating-dem-results-with-fem-perspectives-of-load-soil-interac
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