Th. Zimmermann
ENAC-LSC, Swiss Federal
Institute of Technology, 1015-Lausanne-EPFL,
& Zace Services Ltd, Software engineering,
1015-Lausanne, Switzerland, zimmermann@zace.com
ABSTRACT:
Three-dimensional finite element analyses of underground structures
on PCs are becoming more popular in geotechnical practice. In this
paper, we present some aspects of constitutive and numerical modeling,
and finite element technology and implementation, which are essential
to successful simulations. Implementation in Z_Soil.PC, academic and
real life situations illustrate the discussion.
Recent advances in
numerical software for geomechanics are the result of concurrent progress
in different domains: increased computer performance, advances in software
engineering, unifying theoretical formulations for soil mechanics, and progress
in constitutive and numerical modeling.
Geotechnical engineering is characterized by highly nonlinear mechanics, in multiphase media, with complex initial states, involving complicated geometry. Soil and rock often require the use of multi-surface plasticity models; they also exhibit incompressible or dilating behaviors, which most finite element formulations cannot properly model without enhancements, when using elements with low order interpolation. Since this has been recognized, several types of element improvements have been proposed, which include under-integration, related strain-projection methods, and enhanced assumed strain approaches. We advocate herein a different approach, based on stabilized Galerkin/Least-squares methods, which seems more generic and simultaneously helps to overcome oscillatory pressures known to occur in consolidation simulations, when small time steps are used. Progress has also been made in algorithmic developments. Nowadays geotechnical engineers are more and more often confronted with sites, which are already constructed, which require an accurate definition of the initial state and present a geometrical complexity, which necessitates three-dimensional modeling. More general initial state and stability-analysis algorithms are therefore required.
We present, hereunder, material models
for soil and rock plasticity in section