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Plaxis bulletin 37 2015

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Plaxis bulletin 37 2015

  1. 1. Title Ed Issue 37 / Spring 2015 Plaxis Bulletin PLAXIS 3D analysis of the Groninger Forum Evaluation of the up and down movements of the Vlaketunnel with cyclic analysis using PLAXIS 2D Pavement service life prediction and inverse analysis with PLAXIS 3D
  2. 2. Page14 Table of contents Page4Page6Page10 Colophon Any correspondence regarding the Plaxis Bulletin can be sent by e-mail to: bulletin@plaxis.com or by regular mail to: Plaxis Bulletin c/o Annelies Vogelezang PO Box 572 2600 AN Delft The Netherlands The Plaxis Bulletin is a publication of Plaxis bv and is distributed worldwide among Plaxis subscribers Editorial board: Ronald Brinkgreve Erwin Beernink Martin de Kant Arny Lengkeek Design: Judi Godvliet For information about PLAXIS software contact your local agent or Plaxis main office: Plaxis bv P.O. Box 572 2600 AN Delft The Netherlands info@plaxis.com www.plaxis.com Tel: +31 (0)15 251 7720 Fax: +31 (0)15 257 3107 »The Plaxis Bulletin is the combined magazine of Plaxis bv and the Plaxis users association (NL). The bulletin focuses on the use of the finite element method in geotechnical engineering practise and includes articles on the practical application of the PLAXIS programs, case studies and backgrounds on the models implemented in PLAXIS. The bulletin offers a platform where users of PLAXIS can share ideas and experiences with each other. The editors welcome submission of papers for the Plaxis bulletin that fall in any of these categories. The manuscript should preferably be submitted in an electronic format, formatted as plain text without formatting. It should include the title of the paper, the name(s) of the authors and contact information (preferably e-mail) for the corresponding author(s). The main body of the article should be divided into appropriate sections and, if necessary, subsections. If any references are used, they should be listed at the end of the article. 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 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. Editorial03 04 New developments Evaluation of the up and down movements of the Vlaketunnel with cyclic analysis using PLAXIS 2D 10 PLAXIS 3D analysis of the Groninger Forum 06 PLAXIS Expert Services helped SETEC with complex modelling issues 05 Pavement service life prediction and inverse analysis with PLAXIS 3D 14 Recent activities18 Upcoming events20 Page18
  3. 3. www.plaxis.com l Spring issue 2015 l Plaxis Bulletin 3 »We proudly present to you the spring 2015 edition of the Plaxis bulletin, including three new interesting user articles. The release of PLAXIS 2D 2015 and 2D Thermal module has been made available, and most of our users have already adopted the new version. Currently, we are working hard to deliver the PLAXIS 3D Anniversary Edition, containing several interesting additions in the field of tunnelling, off-shore applications and geomechanics. The new developments column focuses on the features that PLAXIS has implemented recently and will be implementing with regard to Dynamics, a very present-day topic in the Netherlands. We also touch upon our progression in the field of tunnelling and rock mechanics, presenting a new material model for Shotcrete. The first user’s contribution presents work on PLAXIS 3D analysis of the Groninger Forum. The project comprises a 45 meter high building with two basements. The authors investigated the new possibilities, that the staged construction mode available in PLAXIS 3D gives in comparison to their initial design in PLAXIS 3D Foundation. It also discusses the differences between predicted and measured settlements based on their new approach and some suggested actions dealing with large models and some other modelling challenges. In the second user’s article, the up and down movements of the Vlaketunnel with cyclic analysis are evaluated using PLAXIS 2D. The project was performed as an MSc project, in the framework of Infraquest, a research project which investigates the sustainability of immersed tunnels in the Netherlands. The article hypothesizes on a possible cause of movements of the submerged tunnel and proceeds with PLAXIS 2D modelling to investigate the validity of the hypothesis. Other proposed mechanisms are discussed as well, based on the numerical results of several model variations. The third user’s article discusses a pavement service life prediction and inverse analysis with PLAXIS 3D. The author proposes certain workflows incorporating both PLAXIS 3D and Matlab, to perform two separate tasks. In one case, an automated loading analysis to predict the level of damage at the end of 30 years is done, where PLAXIS calculates stresses and these stresses are used in Matlab to assess the damage via an empirical relationship, resulting in a new stiffness for the pavement. This new stiffness is fed into a PLAXIS 3D log file to run the next time step of the full analysis and so on. In the second case, the interactivity between PLAXIS 3D’s log file and Matlab is used to back-calculate stiffness parameters based on measurements of a three dimensional deflection bowl. For the PLAXIS Expert Services update, we review a tailor made in-house training that Plaxis provided to SETEC to get them up to speed on modelling the construction of Evolutionary Power Reactors, which was later supplemented by ongoing advanced analysis support by PLAXIS Expert Services staff. In our recent activities section, some of the events that our Asiapac and Americas offices organized or participated in are discussed. We talk about the activities of the Plaxis headquarters and about the report of the Expedition Masai team which was sponsored by Plaxis. For our worldwide presence on events or hosted courses, we refer you to the upcoming events listed on the backside of the Plaxis Bulletin. We trust that we have provided another issue with engaging content for our readers and we look forward to receiving your comments on the spring 2015 edition of the Plaxis Bulletin. The Editors Editorial
  4. 4. 4 Plaxis Bulletin l Spring issue 2015 l www.plaxis.com for tunnelling in rock as well as for dynamic earthquake analysis. Please contact our sales department to obtain the new shotcrete model or one of the aforementioned user-defined soil models + documentation. It is free of charge for PLAXIS VIP users. We are looking forward to hear about your experiences with these new models. References • Galavi G, Petalas A, Brinkgreve RBJ (2013). Finite element modelling of seismic liquefaction in soils. Geotechnial engineering journal of the SEAGS & AGSSEA, 44(3), 55-64. • Schädlich B, Schweiger HF (2014a). Shotcrete model – Implementation, validation and application of the shotcrete model. Plaxis internal report. Computational Geotechnics Group, Graz University of Technology. • Schädlich B, Schweiger HF (2014b). A new constitutive model for shotcrete. Proc. Numerical Methods in Geotechnical Engineering (eds. Hicks, Brinkgreve, Rohe). Taylor & Francis Group, London, 103-108. New Developments »Engineering consultants and research institutes are investigating the effects of earthquakes on buildings, industry and infrastructure in the province of Groningen. Many of them are using PLAXIS in their analyses. In this respect, it worth mentioning the facilities that PLAXIS has implemented in the past decade for geotechnical earthquake engineering and liquefaction analysis: • Input motion in combination with rigid base or compliant base boundaries • Viscous (absorbing) boundaries, tied degrees- of-freedom (for site response analysis) and free- field boundaries (for earthquake analysis) • Hysteretic damping in HSsmall and Generalised Hardening Soil model (latter available as user- defined soil model) • Rayleigh damping • Cyclic loading and liquefaction in UBC3D-PLM model (available as user-defined soil model) • PSA spectrum and Amplification curves • Consistent mass matrix (more accurate dynamic results; less dispersion) More details about these facilities can be found in a paper by Galavi et al. (2013). Validation reports and documents on the practical use of PLAXIS for site response and liquefaction analysis can be found in the Plaxis Knowledge Base. For those who are new in the field of geotechnical earthquake engineering, it is good to know that we provide support, short courses and in-house trainings with our team of specialists. Besides the ‘excitement’ related to dynamic analysis, there are other new developments worth mentioning. One year ago, I already wrote about PLAXIS’ facilities for rock engineering and tunnelling. Meanwhile, we have developed additional features to enhance the modelling and analysis of tunnels in rock. The upcoming release of PLAXIS 3D AE will have a new tunnel designer with enhanced features to create NATM-type tunnels, including internal sections, loads and lining features. Tunnel contours can be easily extruded along a path before inserting them in the full geometry. Tunnel shapes are now composed of full parametric objects, providing a more accurate and robust description of the tunnel geometry, which also improves the meshing process. In addition, with the release of PLAXIS 2D 2015 last February, a new constitutive model for shotcrete has become available as a user-defined model. This model enables cutting-edge design of sprayed concrete linings by considering the following features of shotcrete (see also Schädlich & Schweiger, 2014): • Time-dependent stiffness and strength (from freshly sprayed to matured shotcrete) • Well-defined failure criterion for tension, compression and shear • Strain hardening and softening (with regularisation) • Creep behaviour • Shrinkage The new ‘structural forces in volumes’ tool (available in PLAXIS 2D) allows for the automatic integration of stresses into structural forces in a tunnel lining modelled by means of the new shotcrete model. As you can see, PLAXIS is well-equipped nowadays The north of The Netherlands (Groningen) is suffering from earthquakes. Not at the Kobe scale, but still very worrying for the people living there. And since the earthquakes are induced by gasexploration, which generates quite some income for the Dutch government, it has become a political issue. Ronald Brinkgreve, Plaxis bv
  5. 5. www.plaxis.com l Spring issue 2015 l Plaxis Bulletin 5 »The complexity of the geological context (general inclination of the soil strata towards the North, anisotropy of the deformation moduli) leads to intensive PLAXIS 3D modelling work in order to: • Justify the structural strength of the gallery • Optimize the geometry of the concrete mass around it • Define the optimal contact conditions to be guaranteed between the mass concrete and the gallery PLAXIS Expert Services team has helped SETEC to achieve their business objectives through accelerated implementation and use of PLAXIS 3D most advanced features. An assistance has been provided in the operation of PLAXIS 3D software applications aiming at: • Providing better use and insight into the applica- tion of the PLAXIS 3D software product • Helping SETEC at being more productive and competitive with respect to FE modelling work now but also for future projects This collaboration consisted in: Customized trainings PLAXIS Expert Services team has created two sets of customized training material based on SETEC specific requirements. With a custom training session, SETEC has also tailored the agenda to cover the information that will benefit its team the most. Model examples that include their typical geometries, materials and design procedures has also been elaborated. In the framework of PLAXIS Expert Services SETEC has been assisted in their simulation work in order to further improve their own capabilities with highly complex modelling issues as being regularly encountered with the EPR UK project. In the context of the construction of the British EPRs (Evolutionary Power Reactor), SETEC has been instructed with the design of the prestressing gallery under the plant at Hinkley point. E. Cazes - F.Cuira, SETEC, France PLAXIS Expert Services helped SETEC with complex modelling issues Analysis support The PLAXIS Expert Services staff was available to support advanced analysis troubleshooting for a wide range of problematic. Short-term support services have been delivered in a timely manner in the filed of meshing optimization process, geometry import, very large number of objects handling. of activity, which foster team responsibility and motivation, as well as allowing for direct contact with clients • Strategic business units make it possible to activate and coordinate the expert knowledge within the various companies in the group to ensure the success of cross-functional projects. "We were very pleased with the very personalized support of the PLAXIS Expert Services Team as well as their involvement with respect to the modeling choices and most relevant simplifications to introduce.” F. Cuira, Technical Director of Terrasol About SETEC SETEC currently has over 2400 employees in more than 40 companies in France and abroad. The SETEC group has two levels of organisation which are the key to its originality and effectiveness: • Numerous relatively small companies, specialising in a particular profession or area The units also accommodate the discussions and innovation work required to achieve constant renewal of core business On the international front, SETEC has set up sites in Europe, Africa and America, wherever its projects take it.
  6. 6. 6 Plaxis Bulletin l Spring issue 2015 l www.plaxis.com The west side comprises only Loam and sand layers. The east side contains in addition a 12-meter-thick heavily overconsolidated clay layer (OCR = 2 to 3), known in the Netherlands as Potklei • The phreatic groundwater level on the west side is 2 m higher than on the east side • Monumental buildings are present very close to the excavation. The most vulnerable dates from the year 1130 AC and is situated at the corner of the excavation • At the final design, the diaphragm wall on the west side is circular shaped, while on the east side it is rectangular The first design was made in 2008, with PLAXIS 3D Foundation. With this program it was only possible to work with horizontal workplanes. The inclining surrounding terrain was therefore schematized by several small vertical steps, see Figure 2. With this 3D model it became clear that the deformations around the building pit are not equal everywhere. Especially at the corners of the excavation pit, the deformations are much smaller. A second, high positioned, temporary strut was added, to decrease the deformations furthermore. Also the water level inside the building pit was increased during excavation under water. With these measures the risk for damages became acceptably low. With the release of the program “PLAXIS 3D” a more detailed schematization of the different building stages and the addition and removal of strut tubes became possible. PLAXIS 3D analysis of the Groninger Forum »The deep excavation required to realize the car park, is designed by ABT (Adviseurs in Bouwtechniek). Diaphragm walls will be the retaining system for the excavation and will be supported horizontally by two layers of steel struts (one at 1.5m and the other at 4.5m depth) and an underwater concrete slab. Tubex Grout Injection Piles (screwed piles with lost tube, lost pile tip and a grout injection) and Gewi anchors avoid uplift failure of the concrete slab. The excavation pit is completely surrounded by adjoining properties, which are within short distances of at least 2.5 m up to 12.5 m. These adjacencies are mainly established on shallow foundation; a single extension is founded on piles. Besides the complexity in the stratigraphy (see Table 1), there is also a geometrical asymmetry in the plan view of the excavation. On the west side, it comprises a semi-circle with a diameter of about 36 m. The east side is roughly a rectangle with 43 m in width and 105 m in length. This sums a total perimeter of 267 m. The bottom of the excavation is located 18 m below the surface. Project challenges There are several reasons to use a three- dimensional finite element program to design the deep excavation: • On the west side the surface level is approximately 2.5 to 3.0 m higher than on the east side • There is a significant difference in soil stratigraphy between the two sides of the excavation (see Table 1) The Groninger Forum will be constructed in the center of Groningen city, the Netherlands. The building is commissioned by the Groningen municipality. This 45-m-height and eccentric-styled cultural center will include a library, museums, cinemas, restaurants and bars. Two basements complete the structure: a five-storey car park (suitable for 390 cars) and a one-storey bicycle parking (suitable for 1,500 bicyles). The car park is located exactly underneath the main structure, whereas the bicycle parking keeps a horizontal distance from it. Figure 1 shows a cross-section of the building and the two basements. M.C.W. Kimenai MSc, senior geotechnical specialist, ABT Figure 1: Cross section of “Groninger Forum”
  7. 7. www.plaxis.com l Spring issue 2015 l Plaxis Bulletin 7 Once the deep struts are laid, more deformation at the East is prevented. Hence, deformations only occur in the vicinity of where the slots are excavated at that time. The vertical deformation of the adjacent structures walk along with the excavation of trenches and laying of the struts (Figure 4). From this feasibility study it can be concluded that the deformations under the nearby adjacent buildings (if the ESBM with a Stage construction possibilities The initial idea of the construction sequence considered that the upper struts are installed before installing the lower ones. The procedure was to remove the upper strut and then place it back a few meters lower at the lower frame. This had to be repeated for each of the struts, having at the end all the lower struts in place and all the upper struts removed. This method was partly inspired by the traditional way of calculating with two-dimensional programs. The second idea was to install only 3 or 4 (at a total of 15) of the upper struts and then advance with the first of the lower struts. However, this approach had a practical constraint: a mobile crane can only lift the 40-ton strut at close range. To overcome this limitation, the following procedure is developed. Only the minimum excavation necessary to install a single strut is made. After the installation, the mentioned excavation is backfilled and only then the complete procedure is repeated for the next strut. This stage construction procedure is hereafter called the ESBM (which stands for local Excavation – Strut installation – Backfilling Method). It should be noted that this approach results in a considerable amount of earthworks, but also in a significant reduction of the excavated volume at a given time. The latter remark means that the soil deformations during the installation of the struts are reduced. Hence, there is the possibility that two layers of struts are not necessary anymore. At least in theory. ESBM with a single layer of struts A feasibility study was started considering only the use of the deep struts (i.e. the lower struts). To this end, a PLAXIS 3D model was made, in which all sub-phases for the laying of the several tubes have been schematized step by step. A number of oblique surfaces were added to the 3D mesh, making it possible to input the aforementioned local excavations inside the main excavation area. Figure 3 shows the volumes representing the local excavations. The excavation-installation-backfill procedure is performed for each strut from East to West until all of them are in place. The remaining soil in the western part of the main excavation prevents deformations of nearby adjacent structures. Layers West-side East-side Surfacelevel NAP + 7,3 m NAP +4,3 m Toplayer (sand, clay, debris) from +7,3 m to +3,0 m from +4,3 m to +0,0 m Loam from +3,0 m to -6,0 m from +0,0 m to -6,0 m "Potklei" - from -6,0 m to -18,0 m Sand, stiff from -6,0 m to -40 m from -18,0 m to -40 m Max depth site investigation -40 m Table 1: Soil stratigraphy Figure 2: PLAXIS 3D foundation model with small vertical steps Figure 3: Extra surfaces in the 3D mesh
  8. 8. 8 Plaxis Bulletin l Spring issue 2015 l www.plaxis.com PLAXIS 3D analysis of the Groninger Forum Modelling challenges The diaphragm walls are not modelled with volume elements but with plate elements. For the struts, beam elements and node-to-node anchors are used. The surrounding soil is modelled as a Hardening Soil (HS) material and to be fully drained (the latter choice is justified since the goal is to compute deformations). Table 2 presents the main soil parameters. The underwater concrete slab is modelled by volume elements with a surface load on top to compensate the upward water pressures (in reality this compensation will be provided by the piles and anchors that are excluded in the simulation). single layer of struts is performed) are significantly lower than when excavating the whole area until the lower struts level at once. Nevertheless, since the deformation levels were in the order of the allowed deformations, it was finally decided not to discard the use of the temporary upper struts. Photo 1 shows the required soil excavation for the placing of the different tubes in the upper and lower layer of struts. Figure 5 shows the detailed modelling in PLAXIS 3D in the final calculation. Figure 6 shows the complete model, which can be compared with the aerial picture of the real situation in Photo 2. All the extra oblique surfaces resulted in a mesh with an important number of elements: more than 500.000. The calculation of the intersections between the soil stratigraphy and the structures (performed by PLAXIS 3D when switching to the tab Mesh) took significant time. But after that, the meshing itself was performed successfully and in a shorter time frame. Different stages had to be calculated using different solvers. The Classic solver used less memory, but it took more time to calculate. The Pardiso solver worked faster, but could give a singular matrix in case of some structural elements. It’s still not clear why. But fortunately, the Picos solver was able to deal with the situation in which structural elements where switched on and soil element where switched off due to the excavation. So, by switching between the different solvers, the whole calculation could be finished efficiently. The calculation of the stages required more than 14 GB RAM-memory and around 30 GB of disk space. To prevent a lack of space available for the Windows temporary folder (TEMP), the project was saved after each phase was calculated. This was done using the commands runner. Monitoring The impact of the excavation on the surroundings is closely monitored, using inclinometers in the diaphragm walls and a large number of measuring bolts in the facades of the adjacent buildings. The estimated horizontal deflection of the diaphragm walls using the PLAXIS 3D model was about 20 to 30 mm. The measured horizontal deformations were smaller: just a few millimetres with a maximum of 7 mm. The lower deformations occurred in reality can be attributed to: • the higher stiffness of the Potklei. The overconsolidation ratio of the clay was not taken into account in the model, which in other words means an underestimation of the initial horizontal stresses and thus in the actual elastic moduli of the HS model • the higher stiffness of the diaphragm wall. In reality, the diaphragm wall showed practically uncracked behaviour, but in the model an elastic modulus corresponding to a cracked wall was considered Moreover, the final measured subsidence of the adjacent structures are lower than the estimated in the model. They are compared in the following paragraph for: a) the buildings at the North and East side of the excavation at a perpendicular distance of 5 m from the excavation and b) buildings at the corners of the excavation, including the monument. As a result of the installation of the various diaphragm wall panels, the measured vertical deformations at the North and East side of the excavation were 1 to 2 mm. The actual excavation and dewatering caused additional vertical deformations of a few millimetres up to 7 mm. The estimated deformations at the North and East side of the excavation were 10 to 15 mm. The monument experienced a settlement of 5 mm, whereas in the model a settlement of 6 mm was estimated. Figure 5: Detailed modelling PLAXIS 3D Figure 4: Vertical deformation of the adjacent structures "walk along" Photo 1: Required local excavation to install a lower strut Loam "Potklei" Sand γ/γsat [kN/m3 ] 19/21 14,5/18,5 19/21 E50 /Eoed /Eur [MN/m2 ] 9/4,5/36 12/6,64/48 110/110/440 c [kN/m2 ] 2,5 20,0 0 ϕ [°] 27,5 17,5 32,5 Table 2: Main soilparameters
  9. 9. www.plaxis.com l Spring issue 2015 l Plaxis Bulletin 9 PLAXIS 3D analysis of the Groninger Forum Figures 7 and 8 show graphs of the measured and calculated settlements as well as the allowed deformation at 4 relevant points. The location of these points are indicated in Figure 6. These figures show that the calculated settlements are less than the allowed, thus the risk of damage of the buildings was acceptably low. The actual measured settlements are lower and some points even showed upward rather than downward movement. This phenomenon could be explained by the fact that, in the model, the upward pore pressures acting at the bottom of the underwater concrete slab were balanced by a non-existent external surface load. Hence, there is an increase in compressive stresses around the bottom of the excavation with a correspondent increase of downward movement. In reality, the Gewi and Tubex piles transfer the force generated by the upward pore pressures to deeper ground layers without increasing the compressive stresses at the bottom of the excavation. Since the excavation produces a reduction in compressive stresses at the bottom of the excavation, the soil around this location will experience an upward movement. Clearly, this leaves the possibility of a net upward movement at the surface, as long as the sum of the settlements experienced by the shallow layers is lower than the sum of upward movements experienced by the deep layers. By adding vertical embedded or volume piles in a PLAXIS model underneath the underwater concrete, the increase of compressive stresses produced by the external load could be avoided. This could result in a more realistic deformation of the surrounding. Alternatively, the external load can be combined with a decreased γsat of the underlying ground layers, in order to reduce the negative effect of the external load. Conclusions With the use of a comprehensive PLAXIS 3D model, including temporary structural elements and a detailed phasing, it is possible to optimize the implementation of a large and complex deep excavation successfully. To calculate more accurate vertical deformations of the surrounding soil mass in case of a deep excavation with underwater concrete, it is important to model the unloading due to the excavation. This could be done by including the tension piles in the model. Figure 7 Figure 6: PLAXIS 3D mesh Figure 8 Photo 2: Photography Koos Boertjens © ABT
  10. 10. 10 Plaxis Bulletin l Spring issue 2015 l www.plaxis.com »The Vlaketunnel is a highway tunnel under the canal through Zuid-Beveland in the A58 road, connecting the city of Bergen op Zoom with Vlissingen. In Figure 1 a top view of the canal with the track of the tunnel is shown. The tunnel sections beneath the canal were built with the immersed tunnel technique. The concrete elements of the tunnel were built in a dock situated just beside the canal. After finishing the construction, the dock was inundated to allow floating of the elements and transportation to the immersion site over water. The elements were immersed into a pre-dredged trench of about 10 m deep. The free space between tunnel and bottom trench was filled up with sand, that was dredged from the Western Scheldt, and formed a foundation layer. Also on either side and on the top of the tunnel sand was deposed; backfill material. To protect the roof of the tunnel against damage caused by falling or dragging ship’s anchors, a stone-asphalt-mattress was installed on the top of the tunnel, see Figure 2. To improve the maritime traffic flow through the canal, in 1993 it was decided to remove the lock at the north side of the canal that closes the canal of the Eastern Scheldt estuary, and as a consequence tidal movements from the North-sea were introduced into the canal. The executive department of the Dutch Ministry of Infrastructure (Rijkswaterstaat) is responsible for the functioning of tunnels in the Netherlands. Deformations and settlements of the tunnels are As part of the InfraQuest research into the sustainability of Immersed tunnels in the Netherlands, a study was carried out at Delft University of Technology to analyze the up and down movements of the Vlaketunnel. InfraQuest is a joint research program of the Ministry of Infrastructure, Delft University of Technology and Delft TNO. The research was done by N. Benhaddou as a final MSc. Project. N. Benhaddou - K.J. Bakker, Delft University of Technology anchors. Mainly due to brittle fracture by pitting corrosion of the anchors and in a certain extent to tide effect, floating of one of the sections of the eastern access ramp is occurred in 2010. The results described in this article are based on the research conducted on the submerged section of the Vlaketunnel. The aim of the research was to determine the physical cause behind the measured up and down displacements of the submerged section. frequently monitored. An evaluation of the data which has been delivered for the Vlaketunnel indicates that the tunnel clearly shows up and down movements, two times daily, coinciding with the tidal movements. Besides the immersed section, the tunnel consists also of access ramps. To prevent the access ramps from floating or shifting upwards, the tunnel sections were provided with tension Evaluation of the up and down movements of the Vlaketunnel with cyclic analysis using PLAXIS 2D Figure 1: Top view of the location of the Vlaketunnel Figure 2: Cross section of the immersed section of the Vlaketunnel
  11. 11. www.plaxis.com l Spring issue 2015 l Plaxis Bulletin 11 Measurements In the context of a monitoring program that was carried out by Rijkswaterstaat, as previously mentioned, measurements had been performed in the tunnel in order to determine the movements of the tunnel as a result of water level changes in the canal. The measurements were performed Figure 4: Graphical view of the daily measurement, April 3 2002 Figure 6: 2D Model, cross section Figure 3: Graphical view of the measurements performed during high and low tide on March 27 - April 12, 2002 Figure 5: (a, left) CPT carried out through the floor of the tunnel in 1975. (b, right) CPT carried out before the realization of the tunnel; (please note that the graph is in kgf/cm2 , and not in MPa, such is customary nowadays). during high and low water periods on March 27 to April 12, 2002. The results of these measurements are graphically represented in Figure 3. The graph shows the ultimate position of the tunnel during a complete tidal cycle. The horizontal axis represents the location of the measurement points along the longitudinal axis of the submerged section. The vertical axis shows the vertical displacement. Figure 4 shows the daily variation in time of tunnel element 1 on April 3, 2002; the blue line in the graph indicates the water level in the canal, on this scale in [m]. The other lines indicate the displacement of fixed points of the tunnel element 1 (which consist of 7 tunnel segments) in [mm].
  12. 12. 12 Plaxis Bulletin l Spring issue 2015 l www.plaxis.com Evaluation of the up and down movements of the Vlaketunnel with cyclic analysis using PLAXIS 2D The stone-asphalt-mattress on the top of the tunnel is modelled with plates and interfaces and assumed to be impermeable. In the first calculation steps the trench excavation and the initial construction of the tunnel was modelled. Afterwards the impact of the tidal wave was added by means of coupled Geo hydro- mechanical analyses with transient hydraulic boundary conditions along the bed of the canal. The pressure profile representing the wave is described by an harmonic time dependent boundary condition with Hs = 3,8 m, as illustrated in Figure 7. To graphically display the results of the analysis, two stress and deformation points are chosen in the middle of the tunnel roof and floor. Results The results of the 2D analysis showed that the immersed section of the tunnel experiences an harmonic upward and downward movements due to the variation in the water level in the canal. During low tide the tunnel comes up, and goes down during high tide, according to the measurements. The calculated displacements are in the order of 9.5 mm between the lowest and highest position. Figure 8 indicates the movements predicted with PLAXIS 2D. The graphs shows clearly that the submerged section of the Vlaketunnel experiences vertical motions that are related to the water level changes in the canal. During low tide the submerged section comes up and during high tide it settles down. An average subsidence and uplift of between 4 and 8 mm respectively, is registered. From the measurements shown in Figure 4 it can be deduced that the tunnel movement and water level changes are not in phase. Maximum water level and maximum subsidence occurs not at the same time. This indicates the presence of a certain resistance by means of (low) permeability of the foundation and the back fill material. A phase shift of up to 1.0 hour is observed. Soil survey In order to infer soil parameters for the sand foundation layer, penetration data, that was realized by CPT testing through the bottom of the tunnel direct after the realization in 1975, was re-evaluated. The CPT data, see Figure 5, shows that the cone resistance of the foundation layer - consist of sand which has been filled into the free space between the bottom of the tunnel and the trench - is about 3 MPa. Below this layer the soil profile mainly consists of loosely packed sand of about 5 meter, followed by the Pleistocene sand. A typical behaviour of loose sand under cyclic loading is contraction and dilatancy. Hypothesis After analyzing the measurements and the soil survey a hypothesis regarding the physical cause of the motions of the immersed section is formulated. It is assumed that the soil beneath the tunnel exhibits elastic behaviour. Directly after the high water peak the saturated subsoil just beneath the immersed section experiences an increase in effective stress. This causes compaction in the loosely packed sand layer and the water is discharged from this layer into adjacent soil profile. After dissipation the tunnel section tends to settle. Directly after the low tide the opposite effect takes place. The now slightly denser sand layer experiences some decrease in effective stress that results in a small expansion of the soil skeleton. Water from the adjacent soil profiles is attracted and the tunnel tends to move upwards. Model Based on the soil survey, which consisted of CPT’s a parameter set was established. The parameters are assumed based on overall experience with soil materials and NEN9997-1. The parameters used are summarized in Table 1. The topology was been modelled as indicated in Figure 6. In order to minimize the effects of the boundaries the geometry has been chosen 100 meter wide and 50 meter deep. The essence of the model is that it describes the deformation of the soil layers beneath the tunnel due to time-dependent variation in the water level. So an integrated Geo hydro mechanical model was established, that includes the time dependent loading on one hand and on the other hand describes the effects of this loading on soil deformation. The tunnel has been modelled as a soil body with linear elastic properties (for concrete). To simulate the interaction between tunnel lining and soil, interface elements were applied. The aim of the analysis was not so much calibrate the exact same value of the displacement as well as to explain the physical principal that is behind the displacements. For that matter the results of the analysis largely confirmed the hypothesis. The supply and discharge of water mainly takes place through the Pleistocene aquifer sand package (Figure 9 and Figure 10). What also leads to the movements is the infiltration of water from the bed of the canal - through the back fill sand next to the tunnel - to bottom tunnel. Infiltration is caused by pressure differences above and beneath the tunnel during high and low tide. Approximately 15% of the total vertical displacement is due to this mechanism. A snapshot of the plasticity in the loosely packed sand layer implies that the presumption that this layer is subject to compression during high water is correct. Due to compaction of the grains, the pore water extruded from this layer. The maximum stress state is then reached, as depicted in Figure 11. The failure points that occur during high tide at the interface between tunnel and soil, implies the up movement of the tunnel. High shear stresses occur on both sides of the tunnel, which means that the soil retains the tunnel to go upwards (Figure 12). Figure 7: Used hydraulic boundary condition in PlaxFlow Tabel 1: Model parameters PLAXIS 2D Figure 8: Predicted up- and downwards movements
  13. 13. www.plaxis.com l Spring issue 2015 l Plaxis Bulletin 13 Evaluation of the up and down movements of the Vlaketunnel with cyclic analysis using PLAXIS 2D References • Kombinatie Vlake (1974) ‘Het onderstromen der tunnelelementen Vlaketunnel’. • InfraQuest (2011) ‘vervormingen van afgezonken tunnels in Nederland’. • Rijkswaterstaat (2010) ‘Metingen zinkgedeelte Vlaketunnel’. • Plaxis bv (2012) Manual 2D ‘Material Models Manual’. The order of magnitude of the movements is strongly influenced by the permeability of back fill sand material and the stiffness of the foundation layer. Whereas the phase shift between tide and movements is mainly influenced by the permeability of the loosely packed sand layer. This has been shown by mean of a sensitivity analysis, whereby the strength, stiffness and permeability parameters of the soil layers were incrementally varied. Removing the stone-asphalt-mattress on the top of the tunnel leads to a slight reduction of the vertical displacement of the tunnel. This has been shown with a calculation where the stone-asphalt- mattress is removed. Effect of the vertical movements on the tunnel as a construction The submerged section behaves under influence of tidal movements in the canal as a long beam with two support point at the end; the maximum displacement occurs in the middle. The up and down movements of the tunnel primarily affect the rubber expansion joints between two adjacent tunnel elements. The movements leads to settlement differences, which results in rotations. For immersed tunnels, the requirement regarding allowable rotation in the joints is determined at 0.0025 rad. The calculated maximum rotation in the joints is 0.001 rad and complies with the requirement. The calculated rotation is determined based on the upper limit for closure level of the Eastern Scheldt Barrier. Conclusions The opening of the canal through Zuid-Beveland to the tidal movements in the Eastern Scheldt Barrier has triggered a soil water interaction that makes the tunnel move up and downward twice a day. The maximum displacement is limited by the level at which the Eastern Scheldt Barrier is closed. The maximum rotations in the tunnel joints stay below the critical limits. The influence of the tidal movements on the tunnel joints on a long term time frame has not been evaluated. Acknowledgments This study was a part of the InfraQuest research into the sustainability of Immersed tunnels in the Netherlands. The authors wish to thank TNO and Rijkswaterstaat, for enabling the performance of this study; thanks are given to Dr. A. Vervuurt of Delft TNO, to facilitate work space and to Mr. Wolsink, for supplying the monitor data and the fruitful discussions on the topic. Figure 9: Illustration water flow towards the tunnel during low tide Figure 11: Occurred plastic points during high tide Figure 12: Occurred plastic points during low tide Figure 10: Illustration water flow off the tunnel during high tide
  14. 14. 14 Plaxis Bulletin l Spring issue 2015 l www.plaxis.com Pavement service life prediction and inverse analysis with PLAXIS 3D »In civil engineering structures, failure occurs when internal stresses exceed their ultimate limit strength. In particular cases, when structures are subjected to repeated loading, failure occurs due to fatigue even if the stresses are much lower than the material strength. Fatigue phenomena can be observed in pavements or structures subjected to dynamic loading, e.g. fatigue of bridge elements. Fatigue is a very complex phenomenon in which material accumulates incremental structural damage due to repeated loading until it reaches failure. The physical damage is induced by micro-cracks that develop in the material, e.g. asphalt. At a macroscopic scale, this means a significant reduction in stiffness. In order to design structures against fatigue, we therefore need to be able to predict the damage development and the consequent stiffness reduction during the service life. Another important issue in the design of pavements or other geotechnical structures is the reliability of soil material parameters, in particular the stiffness. This paper shows how these parameters can be obtained from inverse analysis of pavement deflections and potentially from geotechnical measurements. Service life prediction for pavements The stress levels in a flexible pavement structure are generally much lower than the failure values. Instead, pavement "failure" is due to accumulation of damage and is generally related to structure Predicting the end of service life of an engineering structure, or obtaining parameters from inverse analysis of measured forces or displacements, is a complex task which requires deep knowledge of material behaviour and software development. In this paper it is shown how these two procedures can be carried out by writing a subroutine with the software MATLAB to run with predefined input data, pre- and post-processing a finite element model in PLAXIS 3D. The examples show how it is possible to predict the rest of service life of an airport pavement and to obtain layer stiffness parameters from inverse analysis of a three-dimensional deflection bowl. The developed MATLAB routines allow the field of possible PLAXIS 3D applications to be extended considerably. Carlo Rabaiotti, PhD, Basler & Hofmann AG, 8133, Esslingen (Zurich), Switzerland, contact information: carlo.rabaiotti@baslerhofmann.ch serviceability, in particular the amount of cracks and rutting in the asphalt layer. In the following sections, the methods followed for assessing the development of damage in asphalt and the consequent stiffness reduction are described. Assessment of damage In the adopted method, damage in asphalt is defined based on the number of cycles to failure NF that are obtained as a result of fatigue tests. The (incremental) damage ∆D is obtained by dividing the number of cycles at each calculation step n (e.g. number of load applications in one month) by the number of cycles to failure. D N n F D = (1) Since the number of load cycles to failure NF is not constant, and it varies with temperature, material stiffness and strain amplitude, the fatigue Figure 1: Incremental calculation and accumulation of damage according to Miner's rule. The incremental damage at the calculation step i – 1 is equal to D N n i F 1 i 1 D == = . In the calculation step i the incremental damage becomes D N n i fi D = where, N NF Fi i1 == and the total damage is equal to D Di l i1R D= = (t = temperature, i = increment, e = critical strain)
  15. 15. www.plaxis.com l Spring issue 2015 l Plaxis Bulletin 15 characteristics have in principle to be determined based on a large number of tests under different conditions. In this study, the number of cycles to failure for the asphalt is instead predicted according to the semi-empirical fatigue law that is described in the AASHTO 2008 pavement design guide for alligator cracking. This predictive equation depends on the highest (critical) tensile strain level at the bottom of the asphalt base layer εcrit , the elastic modulus E and empirical coefficients. The total damage D is obtained by adding the increments (Eq. 2) after each iteration according to Miner's rule. D Dii l 1 D= = / (2) Of course, this is a very simple model for the calculation of cumulative fatigue damage (see also Fatemi and Yang, 1998). This approach has been chosen because of its simplicity, and it is still widely accepted for practical applications. Despite its simple formulation, the calculated damage accumulation is non-linear: the incremental damage Di3 is not constant (Figure 1), since NFi depends on the current stiffness and critical strains and climatic (temperature) conditions. Assessment of stiffness reduction due to damage As already discussed, material damage is responsible for the reduction of stiffness in asphalt. In literature there are several approaches to relate damage to stiffness in asphalt (see also Collop and Cebon, 1995). According to a well- known criterion, fatigue failure (100% damage) in asphalt is defined as the number of cycles to failure NF after which the material stiffness (elastic modulus) reaches half of its initial value. Therefore, in the procedure adopted in this paper, the stiffness decay is obtained by multiplying the asphalt elastic modulus by a factor: D 1 2 iRD - (3) The asphalt stiffness is additionally modified at each step based on average monthly layer temperature, according to the well-known Van der Pool monographs. During each iteration, the calculated reduced stiffness is adopted as an input for a new finite element (FE) calculation, and the new critical tensile strains in the asphalt layers are obtained. Once the new critical strains and current stiffness have been obtained, a new value of load applications to failure NFi is predicted and the incremental damage (Eq. 4) and the new stiffness can be assessed again. D N n i Fi D = (4) The iteration procedure stops when the level of damage reaches 100%. The overall procedure is summarized in Figure 2. Algorithm implementation Predicting service life generally requires carrying out hundreds of calculations, one for each calculation step (e.g. 1 month). Therefore an automated procedure needs to be implemented. A major advantage of PLAXIS 3D is that the model can be pre- and post-processed and run under DOS. For pre-processing, a special .log file should be created by the MATLAB-based software with the instructions for the PLAXIS 3D command line. The coded output is then translated into a .txt file with the cbin.exe program. Special software has therefore been written in MATLAB that writes the PLAXIS 3D commands in the .log file and starts the calculation. The critical strains at the bottom of the asphalt base layers are calculated in a three- dimensional finite element model implemented in PLAXIS 3D. After the calculation finishes, MATLAB runs the translating output software cbin.exe and reads the stresses in the gauss points. MATLAB calculates the strains from the stresses according to the elastic constitutive model adopted for modelling the asphalt behaviour. The asphalt stiffness for the next calculation is obtained, as already mentioned, by considering the damage level and the average monthly temperature during service hours of the airport. The procedure is illustrated in Figure 3. Figure 2: Simulation of the damage process due to fatigue in asphalt Figure 3: Implemented procedure for estimating service life (fatigue) with MATLAB (main routine) and PLAXIS 3D (subroutine)
  16. 16. 16 Plaxis Bulletin l Spring issue 2015 l www.plaxis.com Pavement service life prediction and inverse analysis with PLAXIS 3D Assessment of service life for a rehabilitated pavement The software has been successfully adopted for estimating the residual service life of the proposed rehabilitated pavement of runway 14/32 of the Zurich international airport. In this analysis, the ultimate goal was not to identify the period of time until 100% damage would be reached but to predict the level of damage after a period of 30 years. The requirements for the service life duration were defined by the airport authorities. In the following paragraphs a summary of the most relevant information on the modelling is given. More details can be found in Rabaiotti et al. (2013). The pavement and the loading caused by the HSs model. In the implemented code, the results from each calculation step are stored for the next calculation; this means that during the simulation the same model is always loaded and unloaded with updated material properties. Thanks to this feature and the choice of the HSs model for the subgrade, it is therefore possible to follow accumulation of plastic strains (post- compaction) in the unbound (subgrade) layers. In accordance with the airport’s requirements, the performance of the rehabilitated pavement was studied on loading and unloading the finite element model (through the MATLAB routine) for an equivalent period of 30 years. After this time period, the damage was evaluated. the sum of squared error (SSE) between calculated and measured displacements (Figure 6). The procedure is implemented as follows: the MATLAB routine runs the cbin.exe program and translates the PLAXIS output to a readable .txt file. The calculated displacements are read and compared to those measured. The program calculates the objective function (SSE = sum of squared error) and chooses a new set of parameters for its minimization according to the chosen algorithm strategy. It then runs the next PLAXIS calculation with those parameters. This procedure is carried out for several iterations until the minimization value of the objective function is reached. Figure 4a: Symmetrical 3D finite element model of 1/4 of the pavement and load (B777-300ER landing gear). The plot shows the calculated deviatoric stresses q Figure 4b: MATLAB post-processing of pavement displacements calculated with PLAXIS 3D landing gear were reproduced in PLAXIS 3D. Owing to the symmetry of the landing gear (Boeing B777-300ER), it is possible to model only one-quarter of the pavement, and the symmetry boundary conditions are applied accordingly. The model dimensions of 12 x 8 x 6 m (depth) were chosen in order to reduce the influence of the boundary conditions on the calculated results. A plot of the PLAXIS 3D model and an example of the MATLAB post-processing of the results are shown in Figures 4a and 4b. The pavement consists of a layer of asphalt (wearing course and base), cement treated material (sub-base) and subgrade. An interface layer between base and sub-base layer was also modelled. The asphalt and the cement treated base were modelled with a linear elastic constitutive model. The changes in the asphalt elastic modulus due to temperature and damage were calculated by the MATLAB routine within the previously described procedure. The temperatures were obtained from measurements carried out in the layers of an instrumented track nearby, during the years 2003–2005 (Rabaiotti and Caprez, 2007). To model the mechanical behaviour of the subgrade, the constitutive model chosen is the hardening-soil with small strain stiffness (HSs) model. Since the stiffness of the asphalt layers decreases because of damage during the service life, the compression stresses on the subgrade become higher. The increase in the stress level produces irreversible plastic strains in the subgrade; these can be simulated with the adopted Figures 5a and 5b show the development of the temperature-dependent asphalt stiffness and accumulation of damage during the service life. It was found that the proposed rehabilitation design fulfilled the requirements to last for 30 years. Inverse analysis: back-calculation of road material properties based on three-dimensional deflection bowl The procedure for back-calculating the stiffness of a pavement material layer based on a three-dimensional deflection bowl is extensively described in Rabaiotti (2008). The three-dimensional displacement of a pavement under a track load is measured with the ETH Delta test device. The depth and shape of the deflection bowl depend on the layer thickness and stiffness. If the thickness of the layers is known, it is possible to back-calculate the stiffness of the single layers within inverse analysis. The inverse analysis is carried out by seeking the stiffness parameter values that allow a good match to be obtained between the measured and calculated displacements of the pavement. The parameters can be obtained with different strategies (gradient or non-gradient based optimization methods) that are already implemented in the MATLAB Optimization Toolbox. The inverse analysis procedure is carried out in a very similar manner to the simulation of the service life: the parameters (generally Young’s moduli of the individual layers) are chosen by the algorithm in order to minimize the objective function fobj, e.g. In the example presented in this paper, inverse analysis was carried out using ETH Delta measurements (see also Rabaiotti et al. 2013) on runway 16/34 of Zürich international airport. The runway was rehabilitated by replacing the old concrete slabs with an equivalent asphalt layer in 2008. By observing the change of layer stiffness in different runway sections, in particular the heavily loaded initial part (threshold) and lightly loaded middle section, it was possible to quantify the development of the damage in the asphalt. The results are extensively discussed in Rabaiotti et al. 2013. Figure 7 shows the match between back-calculated (lines) and measured (dots) transversal shape of the deflection bowl for different longitudinal wheel positions. Other possible applications The MATLAB software allows for a wide range of future possible applications to be developed. Inverse analysis can, of course, be extended to many geotechnical engineering problems, e.g. back-calculation of soil parameters from deformation of retaining walls of excavations. An interesting field could be the implementation of more advanced statistically based analysis of geotechnical or civil engineering structures, in which the input parameters or even the model geometry can be set according to statistically distributed values. The resulting distribution of the output, e.g. internal forces in the structure, could allow the safety of the structure to be statistically determined.
  17. 17. www.plaxis.com l Spring issue 2015 l Plaxis Bulletin 17 Pavement service life prediction and inverse analysis with PLAXIS 3D Conclusions Simulating the service life of structures subjected to repeated loading (fatigue) or using inverse analysis procedures to determine stiffness parameters, requires the implementation of predictive and optimization algorithms. In the present study, a service life prediction algorithm and an optimization procedure have been implemented in MATLAB. PLAXIS 3D was adopted as a subroutine to calculate the critical strains in the asphalt layer and to simulate the accumulation of damage. The same model, representing the rehabilitated pavement of runway 14/32 at Zürich international airport, was loaded and unloaded with changing asphalt stiffness for an equivalent period of 30 years. It was shown that the proposed rehabilitation was able to fulfill the 30 years' service life requirements. Additionally, a modified version of the MATLAB routine was adopted for inverse analysis of ETH Delta measurements carried out on runway 16/34, which was rehabilitated with the same strategy in 2008. The results of the inverse analysis allowed the development of the damage in the asphalt and cement-treated base layer to be quantified. Linking PLAXIS 3D and MATLAB for pre- and post-processing considerably broadens the field of possible applications for finite element calculations. References • American Association of State Highway and Transportation Officials (AASHTO) (2008). Mechanistic-Empirical Pavement Design Guide, A Manual of Practice, Interim Edition. • Collop A. and Cebon D. (1995). “Modelling Whole-Life Pavement Performance”. Road Transport Technology 4, University of Michigan Transportation Research Institute, pp. 201–212. • Fatemi, A. and Yang, L. (1998). "Cumulative fatigue damage and life prediction theories: a survey of the state of the art for homogeneous materials". Int. J. Fatigue, Vol. 20, No. 1, pp. 9–34. • PLAXIS 3D reference manual (2013). • MATLAB and Optimization Toolbox Release (2013b). The MathWorks, Inc., Natick, Massachu- setts, United States. • Rabaiotti, C. (2008) "Inverse Analysis in Road Geotechnics", PhD Thesis, ETH Zürich. • Rabaiotti, C. and Caprez, M. (2007). Unter- halt 2000, Forschungspaket 4: Dauerhafte Beläge, Schlussbericht zum Forschungsauftrag 2000/422, Bundesamt für Strassenbau, Nr. 1182. • Rabaiotti, C., Amstad, M., and Schnyder, M. (2013) Pavement Rehabilitation of Runway 14/32 at Zürich International Airport: Service Life Pre- diction Based on Updated Incremental Damage Approach. Airfield and Highway Pavement 2013, pp. 609–627. Figure 5a: Decrease of temperature-dependent asphalt stiffness (shear modulus G) during runway 14/32 service life Figure 5b: Accumulation of damage during runway 14/32 service life Figure 6: Inverse analysis procedure, coupling MATLAB (main routine) and PLAXIS 3D (subroutine) Figure 7: Measured (dots) and back-calculated (lines) deflection bowl induced by a track load (twin tyre). The test was carried out on runway 16/34 of Zürich international airport
  18. 18. 18 Plaxis Bulletin l Spring issue 2015 l www.plaxis.com Recent activities PLAXIS 2D 2015 has been released in the first quarter of the year, adding again several new features a new module and scores of improvements to the program. One of several big additions is the new User Defined Soil Model for Shotcrete, which you already read about in the new developments section. Plate elements have been extended with non-linear behaviour, allowing users to specify M-kappa diagrams. The embedded beam row now offers visualization for the connection type and more advanced options for defining lateral skin resistance and axial skin resistance, which users have marked as important to have. A new and more powerful implementation of Sensitivity analysis and Parameter variation has been added as well. In the Output program, a command line is introduced which allows users to retrieve displacements or stresses from objects or coordinates via typed commands. Output has also been extended with the Remote Scripting API, which creates new possibilities for user defined interaction between the Input and Output programs. With the addition of the new 2D Thermal module user can now model the effects of temperature in geotechnical projects. PLAXIS VIP subscribers can contact the Sales department to activate their free license upgrades or request the new Shotcrete Model. Since the last bulletin edition Plaxis has been quite active again to share knowledge with new users and meet with customers. In November Plaxis met new and familiar faces at the annual Hydraulic Engineering Day in the Netherlands, where a lot of companies, governmental bodies, as well as Applied Universities with an interest in anything related to hydraulic engineering came to visit. In the same month, two back-to-back workshops organised at the PLAXIS headquarters in Delft, had participants focused on the subjects of Dynamics and PLAXIS 3D. Plaxis also hosted a workshop on unsaturated soil behaviour at the annual national conference on Geotechnical Engineering and Soil Mechanics in Mexico. The new year started off with the ever popular Standard Course on Computational geotechnics at Schiphol, the Netherlands, drawing people worldwide to learn the very basics of PLAXIS both in terms of the program as well as the scientific background. February was in particular an eventful month in Europe. The fifth edition of the Belgian PLAXIS users meeting was another success. Together with Besix interesting sessions were organized about topics like dynamics and excavations in urbanized settings. In Italy a workshop on tunnelling was held at Arup, Milan. This full day workshop focused on the use of PLAXIS 2D for design and analysis of tunnels, addressing topics like tunnel lining, rockbolts. In Germany, Finite Elemente in der Geotechnik & 3D Analysen - Theorie und Praxis, one of our courses fully lectured in german, was very well attended. Its format is similar to other courses held worldwide, focusing on the more advanced soil models and introducing PLAXIS 3D as well. Middle East After organising several beginner courses in the United Arab Emirates over the past years, Plaxis has held the first Advanced Course in Dubai in October. The course, covering rock modelling, soil improvement and how to get material model parameters from field reports, was attended by delegates from the U.A.E. and the neighbouring countries. In December the second edition of the Turkish PLAXIS users meeting was held in collaboration with Geogrup, our local agent. This event where users presented their own works with PLAXIS and learned a bit about the future development in PLAXIS, was well attended, paving the way for a third one next year. Plaxis Americas In October of 2014 an advanced course was organized in Houston. This busy advanced course brought together a diverse group of engineers from across the US and Canada, most with many years of PLAXIS experience under their belt (some up to twenty years!). The course included an optional day dedicated to offshore geotechnics, topics on that day included cyclic loading effects, NGI-ADP model, seafloor anchors, mud mats, and suction anchors. PLAXIS seminar, South Korea
  19. 19. www.plaxis.com l Spring issue 2015 l Plaxis Bulletin 19 Another focused event was the Tunneling Master Class which was held in February at Columbia University in New York. This full workshop focused on the use of PLAXIS 2D for design and analysis of tunnels, including the 2D Tunnel Designer released in PLAXIS 2D AE. Emphasize was placed on topics relevant to tunneling including soil- structure interaction, groundwater, tunnel lining and rock bolts, and how these can be modeled efficiently using finite element. The brand new and sophisticated Shotcrete User Defined Material Model was explained, and the equally new 2D-Thermal module was briefly touched upon – both are new developments that further enhance PLAXIS’ capabilities for tunnel engineering. Additionally, in the past months many pleasant conversations and productive discussions took place at the Plaxis booth at Dam Safety in San Diego, Canadian Geotechnical Society’s conference in Regina, Deep Foundation Industry conference in Atlanta, and the International Foundations Congress and Equipment Expo (IFCEE) 2015 in San Antonio. We are committed to the North American geotechnical community and will continue to visit and exhibit at events across North America in 2015 and beyond. Make sure to receive our emails, check the list of upcoming events and follow us on social media to see when and where you can meet us in person. We look forward to meet you! Plaxis AsiaPac Two technical seminars on the use of PLAXIS 2D and 3D were conducted on the 26 and 27 of February in Seoul. These two activities were organized by BasisSoft Inc. and PLAXIS AsiaPac. These two application based seminars were attended by local engineers and existing users. We look forward to return to Seoul in the 3rd quarter of 2015 to conduct two advanced application modules. Expedition Masai Plaxis sponsored team “CecileMandy4Masai” for their participation in Expedition Masai 2014, a week long hike in remote highlands and Masai country in Tanzania in support of AMREF Flying Doctors. Dr. Mandy Korff (Deltares, chair of Dutch Geotechnical Society), one of the team members, sent us her report. "Hiking for charity is an ideal combination of adventure and giving back. That is the idea of Expedition Masai, a 5 day charity walk through the Crater Highlands of Tanzania. We depart from our camp on the rim of Empakaai Crater and head north, in the direction of Lake Natron. We walk through remote (high) lands, inhabited by Masai and their cattle. The Masai are proud people and can be seen from far as they dress in bright red colours, which even lions recognize, keeping their distance. The expedition members raised money for AMREF Flying Doctors, and we visit some of their projects during the week. AMREF’s philosophy is to work in small projects, which are owned by the local population. These projects make an immense difference in the life of the people here; general health improves and more girls can go to school because they do not have to carry water all day. We keep these stories in mind while walking through the scenic landscape of the Crater Highlands, grasslands with Acacia trees dotted in. When we descend out of the Highlands towards Lake Natron, the temperature rises above 35 degrees. We pass an air strip where the next day the Flying Doctors actually land, although not more than two lines of rocks in the middle of a sand mass. After 5 days of hiking we reach Lake Natron, with just one small blister, proud and full of admiration for the way the Masai live in this harsh environment. Thanks to the people we met, this week has become so much more than a holiday or sporty adventure. Thanks to our sponsors, especially Plaxis, this has become a walk of appreciation and gratitude, both from the expedition members as well as the people benefitting from AMREF support".
  20. 20. Title 16 Jalan Kilang Timor #05-08 Redhill Forum 159308 Singapore P.O. Box 572 2600 AN Delft The Netherlands Plaxis Americas Office USA Tel +1 650 804 4729 www.plaxis.com Tel +31 (0)15 2517 720 Fax +31 (0)15 2573 107 Plaxis AsiaPac Pte Ltd Singapore Tel +65 6325 4191 Plaxis bv Computerlaan 14 2628 XK Delft 9 April Singapore Plaxis Users Meeting Singapore 13 April Seminario sobre El Uso Practico de Modelos Constitutivos Santiago de Querétaro, Mexico 14 - 17 April Curso Avanzado de Geotecnia Computacional Santiago de Querétaro, Mexico 15 April PLAXIS 2D Workshop for Excavation in Soft Soils Oslo, Norway 10 - 13 May ISRM Congress 2015 Montreal, Canada 19 - 22 May Standard Course on Computational Geotechnics & Dynamics Berkeley, USA 28 - 29 May European Plaxis Users Meeting 2015 Gescher, Germany 2 June Workshop on Advanced Modelling in PLAXIS Delft, The Netherlands 2 June Workshop Utilisation de PLAXIS 2D pour la Modélisation des Fondations en Géotechnique Paris, France 3 June Workshop Dynamics in PLAXIS Delft, The Netherlands 7 - 10 June Rapid Excavation and Tunneling Conference 2015 New Orleans, USA 8 June Introducción al PLAXIS 2D Buenos Aires, Argentina 9 - 12 June Curso Avanzado de Geotecnia Computacional Buenos Aires, Argentina 10 - 12 June International Symposium on Frontiers in Offshore Geotechnics Oslo, Norway 22 - 24 June Curso de Geotecnia Computacional Madrid, Spain 22 - 25 June Standard Course on Computational Geotechnics Manchester, United Kingdom 28 June - 1 July 49th ARMA Rock Mechanics Symposium San Francisco Ca, USA 13 - 17 September ADSO Dam Safety New Orleans, USA 13 - 17 September XVI ECSMGE Conference Edinburgh, United Kingdom 15 - 19 September PLAXIS Advanced Course Melbourne, Australia 20 - 23 September GEOQuébec 2015 Québec, Canada 21 - 24 September PLAXIS Standard Course Brisbane, Australia 7 - 10 October Eurock 2015 & 64th Geomechanics Colloquium Salzburg, Austria 12 - 15 October DFI 40th Annual Conference on Deep Foundations Oakland Ca, USA 13 - 16 October ISGSR Symposium Rotterdam, The Netherlands 3 November Geotechniekdag 2015 Breda, The Netherlands 9 - 13 November 15th ARC Fukuoka, Japan 15 - 18 November XV Pan-American Conference Buenos Aires, Argentina 1 - 2 December STUVA 2015 Dortmund, Germany Upcoming Events 2015 2500 Wilcrest Drive Suite 300 Houston TX 77042 VACANCIES GEOTECHNICHAL ADVISORS (SCIENTIFIC) SOFTWARE DEVELOPERS www.plaxis.com/jobsFore more information about our vacancies please take a look at our website

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