4.10.1 General

A parametric study is a study of the effect on the solution or behaviour of a problem by varying the value of one parameter while keeping all other parameters at a constant or reference value. By doing so, the sensibility of the performance of the problem, in this case excavation, to each model parameter or geometry or others can be identified. The finite element method (FEM) provides the best condition for parametric studies. In this book, the two dimensional FE - program "PLAXIS" version 8.1 is used to perform the parametric studies. Triangular elements with 15 nodes (see Brinkgreve and Vermeer 1998; and Brinkgreve 2002) are used in all the FEM- computations in this section. This element provides a fourth order interpolation for displacements and it involves twelve numerical integration stress points (Gauss points). Basically, the hardening soil model (HSM) is used to simulate the soil behaviour and the Mohr-Coulomb model (MCM) to simulate the interface element. An elastic behaviour is assumed for all structural elements.

The influence of the hardening soil model parameters on the stress - strain, volume change and excess pore pressure behaviour has been discussed in Section 3.3 for a triaxial and one-dimensional compression test condition. Once more, the influence of these parameters on the performance of an idealised excavation are investigated in this section. First, however, the recommendation of the working group "Numerics in Geotechnics" (DGGT AK 1.6) of the German Society of Geo-technical Engineers (MeiBner 2002), regarding the size...