Getting more out of PLAXIS 2D and PLAXIS 3D: Workflow Tips

Micha van der Sloot, Bentley Systems, Inc.

XIII Russian PLAXIS User Meeting | October, 20201

Getting more out of PLAXIS 2D and PLAXIS 3D: Workflow Tips

Micha van der SlootBentley Systems, Inc.Senior Manager, User Success, Geotechnical



Getting more out of PLAXIS 2D and PLAXIS 3DTopics

• More efficient PLAXIS usage

• Getting forces from structural elements

• Importing geometry in PLAXIS



More efficient PLAXIS usage



PLAXIS: More efficient workflow: commandsCommands– All actions using the mouse or the explorers are translated into commands

– All model changes go through it, even when using the mouse

– Direct input of commands possible using command line:

• Session tab: commands executed in the current session

• Model history tab: all the commands executed in the project

– Help → Command reference for all available commands and syntax

– Simple low-overhead syntax

– Offers commands not exposed by the UI tools

– Store and run commands and macros



PLAXIS: More efficient workflow: command lineVisual features on the command line

• syntax highlighting

• error indicators

• comments

Quicker usage of the command line

• recent commands (using ↑/↓)

• Command auto-complete



PLAXIS: More efficient workflow: command runner• When executing more than one command

• Available in Expert menu

• Possible to load command log files

• Copy + paste commands from spreadsheet programs like Excel



PLAXIS: More efficient workflow: macroMacros:

• Possibility to re-use series of commands

• We can store these as series of commands as Macros

• Available in Expert menu

• Macros can have keyboard shortcut:Shift+Ctrl+Alt+[1-9]



PLAXIS: More efficient workflow: macro (2)Extra features: Array indexing syntax

Plaxis stores similar objects in containers / lists:

• Points, Lines, Plates, Phases, and Groups

Listable can be followed by square brackets with integer or a string

• e.g. Points[1], Plates[0], Phases[6], Lines[−1], Interfaces[−2]

• Note: indexing is zero-based!

• Negative numbers count the end of the list

Q: What is a listable?

A: Any object that can be treated as a list:

• Usage: Indexing and commands as e.g. count, filter, tabulate



PLAXIS: More efficient workflow: demo



PLAXIS: More efficient workflow: next?Commands runner and macros

Limitations

• Not much interaction with data

• Results only available in the command line’s Session

• No use of results, values, or arithmetic expressions

• No conditional expressions (if/case) or loops

• No use of external libraries

• No export to files or spread sheets

Great for

• Repetitive commands

• Easy setup of list of commands in text file and spread sheet

Beyond the command line

• Remote scripting interface

• With nice Python wrapper



PLAXIS: More efficient workflow: next: Python



PLAXIS: What level of automation?

Pros Cons

No scripting

Can do (almost) anything PLAXIS can do Repetitive tasks can be boring

Easy to learn Repetitive tasks: time consuming

Built-in command line

Can do anything PLAXIS software can do Cannot script outside a project context

Low learning curve Cannot take runtime decisions (all pre-defined)

Spreadsheets / commands runner / macros for some automation

Remote scripting (Python)

Go beyond native PLAXIS functionality Small upfront investment in learning

Automated actions and decisions at run time Not worth for simple and straightforward projects



Getting forces from structural elements



Getting forces from structural elementsThin wall

Wall thickness << wall length

No end-bearing, only friction

→ Plate element suffices

→ Structural forces direct result (N, M, Q)

Thick wallWall thickness significant

End-bearing capacity needed

→ Use “soil” elements with material set representing wall material

→ In order to obtain structural forces

A) a plate with fictitious properties may be inserted

B) or use structural forces from volumes



Structural forces wall: A) fictious/dummy plate (1)Soil elements with material set representing wall material

Difficult to obtain structural forces from soil elements, therefore introduce plate:

• No influence on deformation: low stiffness, no weight

• Located in on the neutral line (usually the middle)

• Tight bonding to the concrete elements: no interfaces

Assumptions:

• tight bonding of dummy plate with volume-”plate” (εsoil_element = εdummy_plate ; κsoil_element = κdummy_plate)

• presence of the dummy plate should not change result: dummy plate stiffness E should be sufficiently small

d



Structural forces wall: A) fictious/dummy plate (2)How does dummy plate work?

Example: Bending

Soil elements: Esoil_elem = Ereal, Ireal = 1/12*d3 , d = wall thickness

Curvature: M = EI κ → κ = M / EI

κ = κreal = κdummy = Mreal / Ereal*Ireal = Mdummy / EIdummy

→ Let’s take EIdummy sufficiently small, let’s say EIdummy = EIreal / X (with X = 106)

Then Mdummy = Mreal* (EIreal / EIdummy) = Mreal/ X

→ real plate result Mreal = Mdummy * X = Mdummy * 106

Similar for Axial forces

ε = Nreal / Ereal*Areal = Ndummy / EAdummy

→ real plate result Nreal = Ndummy * X = Ndummy * 106

→ Hence, it relies on strain (ε) and curvature (κ)

NOTE: Nwall = Nplate + σy,0 * A, σy,0 = “initial” vertical stress in soil elements

d



Structural forces wall: B) stress integration

→ Hence, it relies on the integrated stresses in the elements

N M N and M

σNσN σN

Str

es

se

sIn

teg

rati

on

: F

orc

es



Structural forces wall: B) stress integrationAlso available in PLAXIS 2D Output

• Select a region or material

• PLAXIS will determine centerline (- - - - -)

• Then cross sections determined

• For each cross section:

• Normal stress σN gives N and M

• Shear stress τ gives Q

→ Hence, it relies on the integrated stresses in the elements

d

σN

N



Structural forces wall: demo case



Structural forces wall: notesDummy plate

• Results not directly available in graph/table (needs factor manually applied)

• Dummy plate needs to be added before analysis

• Large local shear force may not be accurate

Stress integration

• Post processing on any geometry

• Internal cross section determined based on element distribution

• So results can be come inaccurate with too coarse mesh

• Results based on internal stresses

• Be aware of construction sequence

• (WIP/ wished in place)



Importing geometry in PLAXIS



Importing into PLAXIS Importing 2D geometry

dxf, txt

Importing 3D geometry

step, dxf, brep

Importing tunnel geometry

.tnl, dxf

Importing soil investigation: CPT



Import geometry: PLAXIS 2DSupported formats

• DXF: Interchange files

• TXT/CSV: text files (tab-separated values or comma-separated values)

• BRep: Open CASCADE BRep file format

• STEP/STP: Standard for the Exchange of Product model data files

• GEO/STI: Delft GeoSystems M-Series geometry files

Notes

• The DWG file format is no longer supported since PLAXIS 2D 2018

• Lines as part of polylines(AcdbPolyLine) are not imported.

• In the cases where the imported geometry contains curved elements as well (like arcs), the geometry will be partly imported (only points and straight lines).

• Since PLAXIS 2D AE, PLAXIS will not automatically create clusters when lines enclose an area. For this, a polygon needs to be created.



Import geometry



Import geometry: PLAXIS 3DPLAXIS 3D can import different formats

• STEP/STP: "Standard for the Exchange of Product model data" files

• BRep: Open CASCADE BRep file format

• DXF: supports only parametric geometry

• IFC: Industry Foundation Classes files

• Pointcloud from text files



Import geometry: PLAXIS 3D



Import geometry: PLAXIS 3D top surface



After import: Finetune geometry qualityWhy finetune geometry quality?

Goal: good quality mesh to capture geomechanical mechanism

How to finetune?

Detection

Adjustments and repairing



After import: Finetune geometry quality - detect

tabulate volumes and areas[command]

checkgeometry[command][button] NEW

Inspecting geometry — Structures mode

Not only imported geometry, but also

geometry in the model:

• Soil layers from boreholes

• Structural elements



After import: Finetune geometry quality - detectInspecting geometry — Mesh mode

tabulate volumes and areas

checkgeometry [NEW]

Enhanced feedback from mesh generation when using EMR [NEW]

NEW



After import: Finetune geometry quality — detectCommon issues: causes and cases

• Tolerance difference settings between CAD and PLAXIS program

• PLAXIS uses 10−6 [length unit] as tolerance

• CAD image not optimized for FEM but for CAE

• Visually looks OK. For FEM it needs to be “perfect” for mesh creation

• Multiple import geometry: contacting geometry leaves gaps or small overlaps

• Two connecting volumes

• Tunnels with double linings

• Drawing geometry in PLAXIS does not match imported geometry

• Ground anchor connecting to retaining wall

• Plate or beams to connect to a volume



PLAXIS Import: tunnels



PLAXIS Import: tunnel definition



Generate the tunnel



Add tunnel geometry staged construction



Import field data: CPT

3. RobertsonCUR 3

1. Add field data file with CPT data

2. Select which file to use



Import field data: CPT (2D and 3D)



Summary• More efficient PLAXIS usage

• Command line and macros

• Getting forces from structural elements

• Plates: thin and thick

• Structural forces from volumes

• Importing geometry in PLAXIS

• Issues in PLAXIS 2D

• Strategies in PLAXIS 3D

• Tunnel import

• Field data import: CPT

Getting more out of PLAXIS 2D and PLAXIS 3D: Workflow Tips

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