Title Plaxis Bulletin Issue 33 / Spring 2013 Modelling Swelling Rock Behaviour in Tunnelling Editorial South Toulon Tube: Numerical Back-analysis of In-situ Measurements Stability Analysis of the Red River Dike: The Past to the Present Table of contents The Plaxis Bulletin is the combined 03 Editorial magazine of Plaxis bv and the Plaxis users association (NL). The bulletin focuses on the use 04 New developments »of the finite element method in geotechnical engineering practise and includes articles on the Page 5 05 Modelling Swelling Rock practical application of the PLAXIS programs, case studies and backgrounds on the models Behaviour in Tunnelling implemented in PLAXIS. 10 South Toulon Tube: The bulletin offers a platform where users of PLAXIS can share ideas and experiences with Numerical Back-analysis of each other. The editors welcome submission of In-situ Measurements papers for the Plaxis bulletin that fall in any of these categories. 14 Stability Analysis of the Red Page 10 The manuscript should preferably be submitted River Dike: The Past to the in an electronic format, formatted as plain text without formatting. It should include the title Present of the paper, the name(s) of the authors and contact information (preferably e-mail) for the 20 3D Modelling of Frozen corresponding author(s). The main body of the article should be divided into appropriate Ground and Associated sections and, if necessary, subsections. If any Volume Expansion references are used, they should be listed at the end of the article. Page 14 22 Recent activities The author should ensure that the article is written clearly for ease of reading. In case figures are used in the text, it should be indicated where they should be placed approximately in the text. The figures themselves have to be supplied separately from the text in a vector based format (eps,ai). If photographs or ‘scanned’ figures are used the author should ensure that they have a resolution of at least 300 Page 20 dpi or a minimum of 3 mega pixels. The use of colour in figures and photographs is encouraged, as the Plaxis bulletin is printed in full-colour. Page 22 Colophon The Plaxis Bulletin is a publication of Any correspondence regarding the Plaxis For information about PLAXIS software contact Plaxis bv and is distributed worldwide among bulletin can be sent by e-mail to: your local agent or Plaxis main office: Plaxis subscribers [email protected] Plaxis bv Editorial board: P.O. Box 572 Ronald Brinkgreve or by regular mail to: 2600 AN Delft Erwin Beernink The Netherlands Arny Lengkeek Plaxis Bulletin c/o Annelies Vogelezang [email protected] Design: PO Box 572 www.plaxis.nl Jori van den Munckhof 2600 AN Delft Tel: +31 (0)15 251 7720 The Netherlands Fax: +31 (0)15 257 3107 Editorial The Plaxis head office has moved and The third user’s article covers a stability analysis from the begining of this new year we have of the red river dike. The authors compare the started from our new location in Delft. We are very different levels of safety in the past with those »exited about the coming period for Plaxis, and of the present situation by using PLAXIS code expect to be able to provide the valuable products that includes several material models. In stability and services as we have been doing since the analysis, PLAXIS demonstrated successfully the founding of our company in 1993. With this move dike safety factor in flood waves with different we look to the future for 20 more years of success. construction stages. In this issue of the Plaxis bulletin we have again In addition to the contributions by PLAXIS users, tried to collect interesting articles and useful there is an article on 3D modelling of frozen information for you. In the New Developments ground and associated volume expansion where column we take a look at PLAXIS facilities to deal PLAXIS Expert Services provided assistence with with pore pressure in saturated and unsaturated setting-up the models for analysis. conditions. These facilities will also be available in 3D with the relesase of the new 3D PlaxFlow We wish you an interesting reading experience module. The new module is scheduled for release and look forward to receive your comments on this together with PLAXIS 3D 2013 (expected summer 33rd Plaxis bulletin. 2013). The Editors The first user’s article involves the modelling of swelling rock behaviour in tunnelling. The article compares the results of a numerical back analysis of a constitutive swelling model to in-situ measurements, using swelling parameters derived from laboratory swelling tests. The second user’s article is about the South Toulon Tube, and involves a numerical back- analysis on in situ measurements. The numerical model is described and the simulation is validated by comparing it to in situ measurements. The good fitting with the different measurements recorded in situ shows that the three-dimensional numerical modeling, with discretization of the inclusions, is a reliable tool to simulate the complex phenomenon of interaction between the excavation process, the reinforcements and the ground reaction. www.plaxis.nl l Spring issue 2013 l Plaxis Bulletin 3 Title New developments Ronald Brinkgreve, Plaxis bv An important principle in geotechnical engineering is the division of total stress into effective stress and pore pressure. PLAXIS fully supports this effective stress principle. It provides several facilities to deal with pore pressure in saturated as well as unsaturated conditions. Pore pressure, in this respect, is generally pore water pressure, since air pore pressure is ignored. With the release of the new 3D PlaxFlow Module (expected summer 2013), all facilities to deal with pore pressure are available in 2D as well as 3D. The new 3D PlaxFlow Module allows for Dynamic, Consolidation and Fully coupled flow- Backgrounds and further details about the various transient groundwater flow as well as fully deformation) to avoid the generation of suction in possibilities in the new 3D PlaxFlow Module coupled flow-deformation analysis. In the latter the unsaturated zone, equivalent with ‘classical’ are described in the corresponding manuals. »case, pore pressure can change in time as a result calculations based on Terzaghi’s effective stress. With the new implementation we have tried to of (undrained) loading as well as a (simultaneous) The Ignore suction option removes the need for make unsaturated soil behaviour, groundwater change in hydraulic conditions. This involves the different calculation modes. It simplifies the use flow and fully coupled analysis accessible and modelling of partially saturated soil behaviour in of calculation features and the interpretation of understandable for all geotechnical engineers. the unsaturated zone above the phreatic level. The results. We are very keen to know from you if we have behaviour in the unsaturated zone is defined by succeeded in reaching this challenging goal. the soil-water retention curve, which is included in the Flow tab of material data sets for soil & interfaces. Since in most geotechnical projects unsaturated soil data is not available, PLAXIS includes predefined curves for different types of soil. In principle, the unsaturated zone includes suction (positive pore water stress as a result of capillary action). The amount of suction included in the active pore pressure (= effective suction) depends on the degree of saturation, Sr. The latter depends on the selected soil-water retention curve (Fig. 1). For very permeable soils, like coarse sand and gravel, the degree of saturation decreases rapidly with the distance above the phreatic level, whereas in low permeable soils, like silt and clay, the saturation above the phreatic level remains high. Therefore, especially in low permeable soils the influence of suction can be significant. In frictional soils, effective suction provides a kind of ‘artificial cohesion’. In the new 3D PlaxFlow Module, suction can be taken into account when needed, but in many cases it might be desired to avoid the influence of suction on the results. Therefore, the option Ignore suction is available Figure 1: Example of a soil-water retention curve for any type of calculation (Plastic, Safety, y is the suction height above the phreatic level; Sr is the degree of saturation 4 Plaxis Bulletin l Spring issue 2013 l www.plaxis.nl Title Foto by Christian Ammering Modelling Swelling Rock Behaviour in Tunnelling Bert Schädlich & Helmut F. Schweiger, Institute for Soil Mechanics and Foundation Engineering, Graz University of Technology, Graz, Austria Thomas Marcher, ILF Consulting Engineers, Innsbruck, Austria Although a great amount of practical experience has been gained in the last decades, tunnel design in swelling rock is still a very challenging task, as the recent examples of the Engelbergtunnel in southern Germany and the Chienbergtunnel in Switzerland demonstrate. Reliable prediction of swelling pressures and swelling deformations especially in anhydritic rock is extremely difficult due to the heterogeneity of the material and the complexity of the involved transport mechanisms. However, modern design codes and engineering practice demand capacity checks for tunnel linings, which usually can only be provided by numerical analysis with an appropriate constitutive model. Such a constitutive swelling model, which adds swelling strains in dependence on the stress level and accounts for the time dependent evolution of swelling, has been implemented for Plaxis. This article compares the results of a numerical back analysis with this model to in-situ measurements, using swelling parameters derived from laboratory swelling tests. “Swelling rocks” are geomaterials which the material itself, parameters determining the If necessary the time-swell behaviour can be related el increase in volume if water is allowed time-swell behaviour cannot be transferred from to elastic and plastic volumetric strains, ev and pl to infiltrate. The most prominent rock types laboratory tests to large-scale problems.