Post on 11-Sep-2021
transcript
Large scale modeling and simulations with ZSOIL
Rafaª Obrzud 1,2,3
in collaboration withKrzysztof Podle± 3,4, Andrzej Truty3,4
1Karakas & Français SA, 2Rafal Obrzud Ing. Conseil,
3ZACE Ltd., 4Cracow University of Technology
25 August 2017
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Contents
Tackling the large scale modeling and simulations
Hardware requirements
Getting started
Pre-Processing - e�cient model building
Analysis - running, backups and debugging
Post-Processing - troubleshooting and alternative data preview
Selected aspects of modeling
Example of a recent large-scale simulation
Summary
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Hardware requirements
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Hardware requirements
PC or server con�guration for large-scale simulations
RAM - at least 32 GB, 128 - optimal (196 GB - possible)
Processor - One or two multi-thread Intel R©Xeon R©thatsupport large sizes of RAM and 64-bit operating system
Hard drives - those delivering ultimate performance in termsof writing/reading:
modern SSD with PCI-ExpressHDD, 10-12'000 RPM spin speed SATA 6 Gb/s including 64MB cache
Ideally, each large computing on separate physical disk (notpartition)
Display - optimally two 21" panoramic screens
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Getting started
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Getting started
Preliminary assumptions before generation of FE model
1 decide how to generate the model
full 3D macromodeling2D macromodeing followed by extension of 2D FE mesh to 3Dmodelmixed approach
2 try to estimate number of FE elements with respect to theanalysis type, material types
Approximate numbers for ZSoil v2016
Large model 250′000− 500′000 DOFsVery large model 500′000− 1′000′000 DOFsExtremely large model > 1′000′000 DOFs
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Getting started
Excavation and construction stages
anticipate di�erent cases/solutions before model generation;one model may include many di�erent solutions which areactivated using existence functions
de�ne zones of medium to large deformations to optimizemodel extents
try to represent excavation/construction stages as realisticallyas possible
Excavation stages: see VIDEO
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Getting started
Choice of analysis type and material
1 Analysis type:
adapt an adequate type of analysis to the problem you arestudying (steady-state, time-dependent consolidation)make sure that the size of the model is adapted to the analysistype and number of excavation stages (e.g. consolidationrequires 30% more equations)
2 Materials:
use relevant constitutive laws with respect to the goal ofanalysis (e.g. bearing capacity or deformation state)apply adequate constitutive laws to the material that youwould like to describe tomake sure that you have enough data to identify modelparametersmake sure that your theoretical background matches the taskand required constitutive laws
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Pre-processing
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Pre-processing
MESH QUALITY - overview
Mesh quality depends on the shape of elements (ratio hx/hy )
Most accurate results will be obtained for regular (structured)meshes with the aspect ratio approx. 1.0
In 3D, it can be di�cult (we will see how to handle such cases)
Stratigraphy can be automatically generated (in most casesusing Boreholes and Kriging method can be successfullyapplied)
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Pre-processing
MESH REFINEMENT: 1→ 3 scheme
NB. Number of nodes end elements may quickly arise; method also available in 3D
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Pre-processing
MESH REFINEMENT: Nodal Links
1 AUTOMATIC: FE model/Nodal link/Create on aut.sel.nodes-elements
2 SEMI-AUTOMATIC:Select unconnected nodes: Lists/Nodes/select with inconsistent
split
Then use the method: FE model/Nodal link/Create on node(s) -
aut.sel.elements3 Finally, select degrees of freedom to be tied and de�ne EFs
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Pre-processing
Nodal Links:
In 3D analyzes, the nodal link method is especially useful for:
applying nodal forces computed by other engineeringapplications as reactions to a foundation raft analyzed with theaid of ZSoil
applying linear loads to foundation rafts (via arti�cial beams)
connecting struts (trusses) with retaining walls (shells)
tying incompatible meshes of the model, e.g. structural partand the foundation
complex tunnel geometries see VIDEO
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Pre-processing
Nodal Links: examples of applications
Select nodes of the �ctitious beam and then create Nodal linkusing option FE model/Nodal link/On node(s)
Fictitious beam element should be split to get element sizescompatible with the element sizes in the foundation raft (inthis case, length of beam elements should be smaller than ofshell ones)
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Pre-processing
Nodal Links: examples
Mesh re�nement for continuum
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Pre-processing
Nodal Links: examples
Linking structural elements
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Pre-processing
Mesh Tying: creation
Initial nonconforming mesh
Hiddenzone
Create group of edgeswith label
Create group of edgeswith label
NB. Piles, anchors should not cross mesh tying interfaces. The end of these elementsshould not be located in the row of elements adjacent to the mesh tying surface. Thesame applies to nodal links.
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Pre-processing
Mesh Tying: creation
Creating the mesh tying interface is carried out as follows:1 Select edges (2D) or faces (3D) of the �rst part of the mesh and give a label to
them2 Repeat the operation for the second part of the mesh3 Apply the mesh tying technique on interface between a pair of labeled edges or
faces
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Pre-processing
Nodal link vs Mesh tying: Problem statement
Surface load 100 kPa
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Pre-processing
Contours of σy obtained with Nodal Links
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Pre-processing
Contours of σy obtained with Mesh Tying
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Pre-processing
EFFICIENT MODEL BUILDINGAccelerating model generation
Model merging for team working and faster model discretization
prepare the skeleton of the model in CAD application software;*.dxf is the drawing exchange format, for enabling datainteroperability between CAD software and ZSoil
preparation of boreholes, material parameters, entire modelsegments and many other elements can be prepared in separate�les and merged in the very �nal stage of model generation
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Pre-processing
Preparation of model skeleton with CAD applications
Preliminary data preparation and importing *.dxf �le: importingwall contour
Macromodel/Objects/Import from DXF
CAD preview
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Pre-processing
Preparation of model skeleton with CAD applications
Preliminary data preparation and importing *.dxf �le: structuregeometry generated with the aid of CAD application
CAD preview
Assembling macromodel components
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Pre-processing
Merging model data
Importing settings from another inp �le
Main ZSoil window
Dialog for data import
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Pre-processing
Model data merging and fast de�ntion
Direct data editing text (ASCII)*.inp �le
prepare data in Excel �lesor scripts (Python, Matlab,etc.)
use text editor to edit data(e.g. Notepad, Vim)
Example: Finding boreholes by ".gbh"term or borehole labels
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Pre-processing
E�cient work�ow
use names for labeling objects (e.g. loads, anchor, beams, etc.)
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Pre-processing
E�cient work�ow
grouping excavation and load time functions can beadvantageous for faster de�nition or modi�cation of objectsparameters (attributes), e.g. anchors:
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Pre-processing
Accelerating model generation
hide unnecessarily previewed objects
disabling Undo may substantially accelerate Pre-Pro in thecase of very large 3D meshes
think twice before applying changesdo not forget to frequently save your work
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Pre-processing
Tackling complex geometries and intersections
1 Find the most complicated point or expected most deformedzone in the model
2 Use auxiliary surfaces to automatically create intersections
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Pre-processing
Tackling complex geometries and intersections
3 Start generating subdomains around the most complicatedpoint of the model
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Pre-processing
Tackling complex geometries and intersections
4 Gradually expand subdomains creating virtual meshing; thisallows you to control mesh consistency
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Pre-processing
Tackling complex geometries and intersections
5 Use temporary material or existence function numbers tode�ne di�erent zones; it may help and accelerate objectsselection and hiding
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Pre-processing
Troubleshooting before running the simulation
Veri�cation of mesh consistencyOnce a part of virtually meshed subdomains is terminated, execute"Virtual mesh -> Real mesh model", and call node list withinconsistent split.
test split consistency of meshfor selected parts of the model
perform mesh consistency testseven before the completion ofthe �nal model ; you can alwaysremove the generated "Realmesh" and continue working onthe macro model
check multiply nodes
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Pre-processing
Troubleshooting before running the simulation
Veri�cation of mesh consistencyOnce a part of virtually meshed subdomains is terminated, execute"Virtual mesh -> Real mesh model", and call 2DContinuum/3Dcontiunuum/Shell list with inconsistent split.
remove duplicatedobjects
remove elements withnegative Jacobians
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Pre-processing
Troubleshooting before running the simulation
Veri�cation of simulation stages
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Controlling nonlinear computations
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Controlling nonlinear computations
Analysis - running, backups and debugging
Topic covered in the lecture:http://www.zsoil.com/zsoil_course_notes/
large-scale-modeling/large-scale-modeling-2017.pdf38 / 112
Controlling nonlinear computations
Default options for nonlinear solver and time stepreduction/ampli�cation
1 Each driver has an automatic nonlinear solver selection optionswitched ON by default
in 2D, the full Newton-Raphson is set as an initial nonlinearsolver (this strategy requires computation and factorization ofthe global sti�ness matrix at each iteration)in 3D, BFGS is set as a default initial solver being the fastestsolver
2 Divergence triggers switching to another solver
3 Optionally, automatic step reduction can be activated
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Controlling nonlinear computations
Setting an automatic selection of nonlinear solvers andautomatic step reduction
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Controlling nonlinear computations
Troubleshooting during computing
1 not waste preciuos time - verify intermediate stages duringlong-lasting computing runs
2 check *.log �les; some errors associated with modeldiscretization can be reported
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Controlling nonlinear computations
TROUBLESHOOTING using Log �le
Log �le may indicate:
some errors associated with model discretization can bereported
contact overpenetration (maximum normal and tangentgaps in contacts)
rapid divergence -> ill-posed problems or equilibrium issue;check validity of construction stages or kinematics of failuremechanism using Mesh deformation or Color maps withDeformed mesh activated (PgDn/PgUp)
non-convergence -> typically, system about loosingequilibrium, too much plasticity at the same moment, contactissues
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Post-processing
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Post-processing
TROUBLESHOOTING using Postprocessor
Null pivot detected:
indicated in *.log
map of absolutedisplacements showsextreme scale forresults
NB. By setting: , the scale will be adjusted to the visible objects
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Post-processing
TROUBLESHOOTING using Postprocessor
Finding the reason of nullpivot warning:
make visible objectsfor which null pivotcan occur (truss,beam, shell, contact)
activate meshdeformation (PgUp)
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Post-processing
TROUBLESHOOTING in Postprocessor
Finding the reasonof null pivot:
runtroubleshootingmanager
click on nodein the list ofproblems
highlight nodeby clickingSelect
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Post-processing
Paraview as an alternative postprocessor
ParaView: www.paraview.org
is an open source, multi-platform data analysis and visualizationapplication
is known and used in many di�erent communities to analyze andvisualize scienti�c data sets
can be used to build visualizations to analyze data using qualitativeand quantitative techniques
runs on distributed and shared memory parallel and single processorsystems making the data analysis for large scale models verye�ective
is a multi-platform application; ZSoil-produced data sets can bevisualized using di�erent operational systems (Windows, MacOS X, Linux, etc).
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Post-processing
Paraview as an alternative postprocessor
Since 2016, ZSoil has been o�ering the new feature that allowsZSoil results to be exported to the �le formats that ParaViewunderstands.
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Post-processing
Paraview as an alternative postprocessor
possibility of applying di�erent graphical �lters
horizontal displacement
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Post-processing
Paraview as an alternative postprocessor
e�ective inspection with the aid of sections
settlement
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Post-processing
Paraview as an alternative postprocessor
customizing output variables using the Calculator �lter
map of reaction coe�cient computed for interface results (σn/uy )
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Post-processing
Paraview as an alternative postprocessor
How to visualize the color map of reaction coe�cient ks?
1 In ZSoil, export interface data to paraview format (you don't have toexport all data but you can if you need them for other purposes); considerthe reference time step if needed, especially for displacements (contacttypically appears with the structure)
2 In ParaView, open �le "�lename_cn_timeInstance.vtu". These areinterface results only for a given time instance. Click on Apply to plot thedata.
3 Apply "Cell Data to Point Data" �lter. It allows to interpolate normaltotal stresses from central Gauss points (average value for 4 Gausspoints) to nodes at which displacements are computed
4 Apply "Calculator" �lter. It allows to de�ne a custom output based ondata which are collected in data vectors or scalars.
Visualizing ks : see VIDEO
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Post-processing
Paraview as an alternative postprocessor
useful for troubleshooting (discontinuities can be detected)
real-time animationsSimulation of a tunnel excavation see VIDEO
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Selected aspects of modeling
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Selected aspects of modeling - shells
Slim vs thick shells
Two types of shell elements are available in 3D:
shell one layer - represented by in�nitely slim surface
shell - explicitly re�ects geometry in three directions
Typical applications:
"Slim" shell one layer "Thick" shell• Sheet pile walls, relatively slimslurry walls
• Slurry walls, especially thick onesand/or signi�cantly loaded on thetip
• Floor slabs • Foundation rafts• Slim temporary tunnel supports • Tunnel linings
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Selected aspects of modeling - shells
Thick shells - examples
Retrieving bending moments in foundation raft
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Selected aspects of modeling - shells
Thick shells - examples
System of thick shells to represent diaphragm walls
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Selected aspects of modeling - shells
Thick shells - general remarks
slim shells are regarded as Q4 elementsand can be created on B8 continuum
the same set of results is computed asfor slim shells
contrary to slim shells, hydraulic orthermal conductivity is handled
the master (red) and slave (green)faces must lie on the same planes; useFlip or Set master(s) on face(s)
anchors, beams, thins shells should beattached to the master surface
Adjustment of master faces:wrong correct
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Selected aspects of modeling - shells
Thick shells - treatment of corners
corner connection can be discretized in di�erent manners:
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Deep excavation adjacent to a
metro station in Geneva
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Metro station O'Vives in Geneva
Problem statement
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Metro station O'Vives in Geneva
Spring 2017
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Metro station O'Vives in Geneva
Problem statement
Tunnel cross-section Imposed veri�cation scheme
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Metro station O'Vives in Geneva
Modeling of the tunnel structure
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Metro station O'Vives in Geneva
Construction stages: preliminary earthworks
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Metro station O'Vives in Geneva
Construction stages:Diaphragm wall installation followed by shallow excavation
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Metro station O'Vives in Geneva
Construction stages:Construction of �oors above the metro platform
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Metro station O'Vives in Geneva
Construction stages:Excavation below the constructed �oors
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Metro station O'Vives in Geneva
Construction stages:Installation of 2 rows of anchors in the unsupported centralpart
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Metro station O'Vives in Geneva
Construction stages:Bottom of the tunnel excavation achieved
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Metro station O'Vives in Geneva
Construction stages:Excavation for Lot A
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Metro station O'Vives in Geneva
Construction stages:Preparatory earthworks and installation of diaphragm wall
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Metro station O'Vives in Geneva
Construction stages:Preparatory earthworks and installation of diaphragm wall
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Metro station O'Vives in Geneva
Construction stages:Construction beginning of Lot A
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Metro station O'Vives in Geneva
Construction stages:Excavation beginning Lot D3, construction of the structureLot A
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Metro station O'Vives in Geneva
Construction stages:Continuation of excavation for Lot D3, gradual constructionof the structure Lot A
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Metro station O'Vives in Geneva
Construction stages:End of excavation for Lot D3, gradual construction of thestructure Lot A
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Metro station O'Vives in Geneva
Construction stages:Excavation beginning for Lot D1-D2, gradual construction ofthe structure Lot A
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Metro station O'Vives in Geneva
Construction stages:Excavation for Lot D1-D2, construction of the �rst �oors inD3
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Metro station O'Vives in Geneva
Construction stages:Excavation end in Lot D1-D2, construction of the next �oorsin D3
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Metro station O'Vives in Geneva
Construction stages:Beginning of the construction in Lot D1-D2
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Metro station O'Vives in Geneva
Construction stages:Beginning of the construction in Lot D1-D2
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Metro station O'Vives in Geneva
Construction stages:Gradual construction in Lot D1-D2
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Metro station O'Vives in Geneva
Construction stages:End of underground parking construction in Lot D
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Metro station O'Vives in Geneva
Construction stages:Interaction conditions between the metro station walls andLot D2
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Metro station O'Vives in Geneva
Construction stages:Interaction conditions between the metro station walls andLot D3
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Metro station O'Vives in Geneva
Construction stages:Realization of the �oors in the central part
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Metro station O'Vives in Geneva
Construction stages:Removal of the temporary anchors and application of totalloads
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Metro station O'Vives in Geneva
Kinematics of diaphragm wall during construction works
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Metro station O'Vives in Geneva
Deformation of diaphragm wall during construction works
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Metro station O'Vives in Geneva
Deformation of diaphragm wall during construction works
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Metro station O'Vives in Geneva
Deformation of diaphragm wall during construction works
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Metro station O'Vives in Geneva
Deformation of diaphragm wall during construction works
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Metro station O'Vives in Geneva
Deformation of diaphragm wall during construction works
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Metro station O'Vives in Geneva
Deformation of diaphragm wall during construction works
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Metro station O'Vives in Geneva
Deformation of diaphragm wall during construction works
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Metro station O'Vives in Geneva
Deformation of diaphragm wall during construction works
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Metro station O'Vives in Geneva
Deformation of diaphragm wall during construction works
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Metro station O'Vives in Geneva
Deformation of diaphragm wall during construction works
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Metro station O'Vives in Geneva
Deformation of diaphragm wall during construction works
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Metro station O'Vives in Geneva
Deformation of diaphragm wall during construction works
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Metro station O'Vives in Geneva
Deformation of diaphragm wall during construction works
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Metro station O'Vives in Geneva
Deformation of diaphragm wall during construction works
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Metro station O'Vives in Geneva
Deformation of diaphragm wall during construction works
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Metro station O'Vives in Geneva
Deformation of diaphragm wall during construction works
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Metro station O'Vives in Geneva
Deformation of diaphragm wall during construction works
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Metro station O'Vives in Geneva
Deformation of diaphragm wall during construction works
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Metro station O'Vives in Geneva
Deformation of diaphragm wall during construction works
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Metro station O'Vives in Geneva
Control of cracking appearance in mezzanine �oor
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Summary
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10 commandments for the FE modeler
1 Gradually adapt the level of model complexity to your experience; itis not recommended create large scale models before preforming lessdemanding 3D simulations
2 "Create models as simple as possible but not simpler"; carefullystudy geotechnical reports and demanded tasks to adapt anadequate analysis type, materials, geometries and types of FEobjects
3 Make sure that your theoretical background allows you toconsciously use the theories which are included in your model; ifnot, read manual, reports, literature, discuss with other users andperform basic, elementary simulations to verify applicability ofprogrammed elements and constitutive laws; driving a Ferrari withVespa driving license is not recommended
4 Prepare high quality meshes; more you spend on generating themesh, faster you perform the computing and model debugging
5 Large scale models should be tested �rst using elastic materials butconsidering true contact interfaces
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10 commandments for the FE modeler
6 In general, it is impossible to solve unsolvable problems; beforerunning calculations verify construction/excavation stages andboundary conditions in pre-processor
7 Carefully include all meaningful excavation/construction stageswhich are planned to be executed, and anticipate di�erentgeometrical or analysis cases during mesh generation
8 At the early stage of the project, make assumptions on the safe side;it is easier to overlook some nuances if everything goes fantasticstarting from the �rst computing
9 Do not panic if a divergent or non-convergent step occurs; try toanalyze the source starting from checking boundary conditions(usually for water pressures), model geometry (mesh splitinconsistencies), excavation/construction stages (typically wrongorder), and �nally, the material data
10 If you exhausted all your ideas trying to understand what's wrong,or you believe that it can be a bug in the code, send a zipped inp�le with a short description of the issue to hotline@zsoil.com
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