Continuum and Discrete Modelling of Penetration Problems

Penetration of rigid bodies into the ground are ubiquitous in geotechnical engineering. Their numerical modelling involves significant challenges because of the strong nonlinearities arising from large deformations/displacements, contact formulations and constitutive laws. Two alternative simulation strategies are explored and discussed: continuum and discrete modelling. For continuum modelling, the G-PFEM method (i.e. the particle finite element method for geotechnical applications) is selected and described. G-PFEM is based on a Lagrangian description of motion, the use of low order finite elements and the constant re-generation of the finite element mesh. The method has been extended to deal with coupled hydromechanical analyses, required by a proper simulation of geotechnical problems in terms of effective stresses. A number of enhancements of the formulation to make the analyses robust and practical are described. The successful application of the method is illustrated in penetration problems involving the insertion of a tube sampler and the CPTu test into brittle soil. Alternatively, discrete approaches are advantageous in cases where the dominant phenomena occur at particle level as, for instance, in the case of crushable sands. The suitability of the discrete element method (DEM) to reproduce the cone penetration test in a crushable granular material is demonstrated.