Numerical modeling of geotechnical structures

Numerical modelling of geotechnical structures, in particular using finite element or finite difference methods, has become increasingly popular over the last fifteen years as computing power and computer memory capacities have grown ever faster.

Three-dimensional calculations involving several hundred thousand nodes are now commonplace. They not only provide access to the field of displacements, deformations and stresses, both in the ground and in various structural elements, but can also provide information on the level of safety, particularly with procedures for reducing shear properties.

However, if poorly executed, these calculations can lead to erroneous interpretations in the dimensioning of geotechnical structures, and it is therefore more necessary than ever to know and master the most important aspects of numerical modeling.

The links between numerical calculations and the justification procedures of dimensioning standards, in particular Eurocode 7, are also an important aspect to consider.

Modeling strategy remains a fundamental step in all geotechnical modeling. It must lead to a choice between two- or three-dimensional calculations, plane deformation or axisymmetry, identification of the hydraulic and thermal couplings to be considered, definition of the relevant boundary conditions, and so on.

Behavioral models are another essential part of any numerical model, and the engineer in charge of the calculations needs to understand how they can affect the results he will have to analyze. The effects of the various parameters can only be controlled if their roles in the calculation are precisely identified.

Soil-structure interaction is also an essential part of all numerical modeling. Two aspects need to be taken into consideration: the structural element as such and its modeling in the form of a bar, beam or shell, etc., and the interface elements that link these structural elements to the volumetric elements modeling the ground in place.

Other more recent techniques, such as macroelements, are becoming an interesting alternative in certain cases.

Finally, results analysis is an important phase in numerical modeling. Checking that the calculations have converged correctly is the first step, and must be followed by analysis of displacements, deformations and stresses.

Shear property reduction procedures have now become a common tool for assessing a safety factor relating to the mobilization of ground resistance. However, the results obtained from these procedures need to be carefully analyzed, particularly in the case of interaction between volumetric and structural elements....