Modeling of ground excavation with the particle finite element method

Abstract

The present work introduces a new application of the Particle Finite Element Method (PFEM) for the modeling of excavation problems.

Lagrangian descriptions of motion of the continuum medium are the natural way of describing motion in solid mechanics. Particle finite element methods are based in these solid mechanics settings that can treat large material deformations and rapidly changing boundaries.

These capabilities are very suitable for modeling fluid motions and moving free surfaces. That is the reason that the most of the research and applications of PFEM can be found in the context of computational fluid dynamics (CFD) instead of solid mechanics. The satisfying results in modeling fluids have been the motivation to use this method in dynamic solid mechanics.

The simulation of an excavation process is a non-linear dynamic problem. It contains geometrical, material and contact non-linearities. Modeling the contact process can be classiffied as the main difficulty. The simulation face the problems of: the detection of a changing geometry, the detection of contact between several solid domains, the estimation of correct interacting forces, the computation of the wear related to this contact forces and the removing of the material that has been excavated from the model.

The PFEM have its fundamentals in the classical non linear finite element analysis. The formulation provides a foundation in the updated lagrangian formulation for solids. The dynamic problem is integrated using an implicit scheme. Remeshing strategies are employed in order to identify the boundary surfaces. A remeshing of the domain is introduced for the detection of rapidly changing boundaries. The Delaunay tessellation and the alpha-shape concept together, are used as a methodology to de_ne the boundary from a cloud of points. At the same time an interface mesh is created for contact recognition. A particular constitutive contact law has been developed for capturing contact normal and frictional forces using this mesh.

By means of an Archard-type law, the excavation and damage caused in the ground is quantified. The erosion and wear parameters of the grounds under study determine the excavability. The behavior of the geomaterials is described using a Damage Model which model fracture in the continuum. The update and storage of the variables in particles have especial schemes for its correct treatment. The method and the meshing process is adapted for the simulation of an excavation problem.

PFEM is presented as a very suitable tool for the treatment of excavation problem. The method gives solution for the analysis of all processes that derive from it. The method has a high versatility and a reasonable computational cost. The obtained results are really promising.

References

See pdf document