Tunnel modelling: stress release and constitutive aspects

Tunnel construction in soft ground has evolved significantly over the last 20 years, especially on the matter of settlement control. This was achieved by guiding theTBM operation to control the main factors that induced soil displacements, like the face pressure and the soil-lining void closure. However, the design methods and numerical modeling procedures where not adapted to these new conditions, sometimes applying boundary conditions, constitutive parameters or state variables with no physical meaning to match field measurements. This paper presents an analysis of the basic principles of plane strain numerical modeling of tunnel construction. The literature review is followed by an analysis of the stress release factor and the effects of different constitutive models to represent the soil. The tunneling convergence and settlement trough as well as the stress paths on soil elements at the crown and at springline will be presente

Reuleaux plasticity: improving Mohr-Coulomb and Drucker-Prager

The yielding of soil exhibits both a Lode angle dependency and a dependency on the intermediate principal stress. Ignoring these leads to a loss of realism in geotechnical analysis, yet neither of the widely used Mohr-Coulomb (M-C) or Drucker-Prager (D-P) models include both. This paper presents a simple pressure-dependent plasticity model based on a modified Reuleaux (mR) triangle which overcomes these limitations and yet (like the M-C and D-P formulations) allows for an analytical backward-Euler stress integration solution scheme. This latter feature is not found in more sophisticated (and computationally expensive) models. The mR deviatoric function is shown to provide a significantly improved fit to experimental data when compared with the M-C and D-P functions. Finite deformation finite-element analysis of the expansion of a cylindrical cavity is presented, verifying the use of the mR constitutive model for practical analyses

Site investigation for the effects of vegetation on ground stability

The procedure for geotechnical site investigation is well established but little attention is currently given to investigating the potential of vegetation to assist with ground stability. This paper describes how routine investigation procedures may be adapted to consider the effects of the vegetation. It is recommended that the major part of the vegetation investigation is carried out, at relatively low cost, during the preliminary (desk) study phase of the investigation when there is maximum flexibility to take account of findings in the proposed design and construction. The techniques available for investigation of the effects of vegetation are reviewed and references provided for further consideration. As for general geotechnical investigation work, it is important that a balance of effort is maintained in the vegetation investigation between (a) site characterisation (defining and identifying the existing and proposed vegetation to suit the site and ground conditions), (b) testing (in-situ and laboratory testing of the vegetation and root systems to provide design parameters) and (c) modelling (to analyse the vegetation effects)

Geautomatiseerde parameterbepaling in de geotechniek

De grondmechanica of geotechniek is van oudsher een vakgebied van specialisten. Maar dit vakgebied staat ook bekend als 'conventioneel'. Veranderingen en technologische ontwikkelingen gaan vaak niet zo snel als in andere vakgebieden. En de geotechniek heeft een ander probleem: de processen in de ondergrond zijn weinig zichtbaar. Daar waar projectontwikkelaars vaak wel geld over hebben voor een mooi uiterlijk van een gebouw, wordt een investering in grondonderzoek meestal als 'kostenpost' gezien waarop zoveel mogelijk wordt bespaard. Toch is grondonderzoek van essentieel belang om ervoor te zorgen dat een gebouw of de constructie blijft staan en niet (te veel) verzakt

Geautomatiseerde parameterbepaling in de geotechniek

De grondmechanica of geotechniek is van oudsher een vakgebied van specialisten. Maar dit vakgebied staat ook bekend als 'conventioneel'. Veranderingen en technologische ontwikkelingen gaan vaak niet zo snel als in andere vakgebieden. En de geotechniek heeft een ander probleem: de processen in de ondergrond zijn weinig zichtbaar. Daar waar projectontwikkelaars vaak wel geld over hebben voor een mooi uiterlijk van een gebouw, wordt een investering in grondonderzoek meestal als 'kostenpost' gezien waarop zoveel mogelijk wordt bespaard. Toch is grondonderzoek van essentieel belang om ervoor te zorgen dat een gebouw of de constructie blijft staan en niet (te veel) verzakt.Geo-engineerin

Geomaterial Models and Numerical Analysis of Softening

Civil Engineering and Geoscience

The future of the finite element method in geotechnics

In this presentation a vision is given on tlie fiiture of the finite element method (FEM) for geotechnical engineering and design. In the past 20 years the FEM has proven to be a powerful method for estimating deformation, stability and groundwater flow in geoteclmical stmctures. Much has been achieved in terms of advanced models for soil behaviour, 3D modelling and meshing, realistic simulation of soil-structure interaction and constmction stages, robust numerical procedures, parallel processing and visualization of results. New challenges for the FEM are how to deal with Eurocode 7, heterogeneity ofthe ground, large defonnations and flow of materials, coupling of different physical and engineering processes, availability of data (using the intemet), and, last but not least, the required loiowledge and expertise of the user. A discussion point is to what extend the user of geotechnical finite element software needs to Imow the fundamental backgrounds of the 'engine' as long as he/she understands the possibilities and limitations. Is there a need for a 'driving licence', and who should issue the Ucence?Geoscience & EngineeringCivil Engineering and Geoscience

Efficient modelling of pile foundations in the finite element method

Geoscience & EngineeringCivil Engineering and Geoscience