large scale modeling and simulations with zsoil

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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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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http://www.zsoil.com/zsoil_course_notes/large-scale-modeling/anim_excavation_stages/anim_excavation_stages_player.html

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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http://www.zsoil.com/zsoil_course_notes/large-scale-modeling/anim_excavation_stages/LEB_VIDEO_2.html

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


3 Start generating subdomains around the most complicatedpoint of the model

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Pre-processing


4 Gradually expand subdomains creating virtual meshing; thisallows you to control mesh consistency

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Pre-processing


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


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


Veri�cation of simulation stages

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Controlling nonlinear computations

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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

http://www.zsoil.com/zsoil_course_notes/large-scale-modeling/large-scale-modeling-2017.pdf

http://www.zsoil.com/zsoil_course_notes/large-scale-modeling/large-scale-modeling-2017.pdf


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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Setting an automatic selection of nonlinear solvers andautomatic step reduction

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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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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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www.paraview.org

Post-processing


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


possibility of applying di�erent graphical �lters

horizontal displacement

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Post-processing


e�ective inspection with the aid of sections

settlement

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Post-processing


customizing output variables using the Calculator �lter

map of reaction coe�cient computed for interface results (σn/uy )

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Post-processing


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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http://www.zsoil.com/zsoil_course_notes/large-scale-modeling/paraview-customized-output-ks/paraview-customized-output-ks_player.html

Post-processing


useful for troubleshooting (discontinuities can be detected)

real-time animationsSimulation of a tunnel excavation see VIDEO

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http://www.zsoil.com/zsoil_course_notes/large-scale-modeling/anim_tunnel_LEB_dispY/anim_tunnel_LEB_dispY_player.html

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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Thick shells - examples

Retrieving bending moments in foundation raft

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Thick shells - examples

System of thick shells to represent diaphragm walls

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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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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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Spring 2017

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Problem statement

Tunnel cross-section Imposed veri�cation scheme

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Modeling of the tunnel structure

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Construction stages: preliminary earthworks

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Construction stages:Diaphragm wall installation followed by shallow excavation

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Construction stages:Construction of �oors above the metro platform

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Construction stages:Excavation below the constructed �oors

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Construction stages:Installation of 2 rows of anchors in the unsupported centralpart

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Construction stages:Bottom of the tunnel excavation achieved

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Construction stages:Excavation for Lot A

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Construction stages:Preparatory earthworks and installation of diaphragm wall

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Construction stages:Preparatory earthworks and installation of diaphragm wall

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Construction stages:Construction beginning of Lot A

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Construction stages:Excavation beginning Lot D3, construction of the structureLot A

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Construction stages:Continuation of excavation for Lot D3, gradual constructionof the structure Lot A

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Construction stages:End of excavation for Lot D3, gradual construction of thestructure Lot A

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Construction stages:Excavation beginning for Lot D1-D2, gradual construction ofthe structure Lot A

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Construction stages:Excavation for Lot D1-D2, construction of the �rst �oors inD3

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Construction stages:Excavation end in Lot D1-D2, construction of the next �oorsin D3

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Construction stages:Beginning of the construction in Lot D1-D2

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Construction stages:Beginning of the construction in Lot D1-D2

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Construction stages:Gradual construction in Lot D1-D2

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Construction stages:End of underground parking construction in Lot D

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Construction stages:Interaction conditions between the metro station walls andLot D2

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Construction stages:Interaction conditions between the metro station walls andLot D3

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Construction stages:Realization of the �oors in the central part

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Construction stages:Removal of the temporary anchors and application of totalloads

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Kinematics of diaphragm wall during construction works

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Deformation of diaphragm wall during construction works

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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 [email protected]

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[email protected]

large scale modeling and simulations with zsoil

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