Bentley Communities
Bentley Communities
  • Site
  • User
  • Site
  • Search
  • User
  • Welcome
  • Products
  • Support
  • About
  • More
  • Cancel
GeoStudio | PLAXIS
  • Product Communities
GeoStudio | PLAXIS
GeoStudio | PLAXIS Wiki Safety analysis and undrained behaviour
    • Sign In
    • -Geotechnical Analysis Wiki
      • +GeoStudio
      • -PLAXIS
        • +Software and License - PLAXIS
        • +Documentation - PLAXIS
        • +API / Python scripting - PLAXIS
        • +Known issues - PLAXIS
        • +Models - PLAXIS
        • -Tips and Tricks
          • 3D Extrusion along a curved path
          • 3D Output: show results for shadings or contour lines
          • 64 bit User Defined Soil model
          • After a consolidation analysis I have excess pore pressures in "drained" material sets. Why?
          • An error occurred in the application – What to do
          • Application of commands: echo
          • Application of commands: Groupfiltered and Apply
          • Application of commands: Referring to objects through their index
          • Calculation Kernel Convergence log
          • Can I import a geometry in PLAXIS 2D?
          • Can I reuse existing PLAXIS 3D geometrical objects in a new project?
          • Change temporary folder for intermediate calculation data files
          • Closing PLAXIS after your calculation is finished
          • CodeMeter network error during calculation (IPv4/v6 conflict)
          • Codemeter Network Installation
          • Codemeter USB Stick behaviour
          • Command line reference
          • Compliant base and free field boundaries: check on input signal
          • Composite liner approach in PLAXIS 2D
          • Connect a node-to-node anchor with an embedded beam row halfway
          • Considerations for modelling a thick slab as a plate
          • Consolidation: Minimum Pore Pressures and Degree of Consolidation analysis may give spurious displacements of boundary nodes
          • Conversion from 2D Version 8/9
          • Conversion of PLAXIS 2D files
          • Copy/Array command in Plaxis 2D
          • Create centerline for Structural Forces in Volumes
          • Create rock bolts accurately in PLAXIS 3D
          • Creating axial force curve for Fixed End anchors
          • Deactivated loads are still visible in PLAXIS Output
          • Definition of a bending moment as load
          • Definition of Hoek-Brown model parameters in Plaxis
          • Drained Settlement Vs. Consolidation: Differences at Failure in Output
          • Drift correction for dynamic input signal from file
          • During a calculation some plastic points disappear. How is that possible?
          • Dynamic Load with Perpendicular Distribution
          • Encrypted scripting server vulnerable to replay attacks
          • End bearing of plates
          • Energy saving while running multiple calculations
          • Error when generating 3D mesh
          • Export and format plots from PLAXIS Output
          • Export or reuse geometry for New Analysis
          • Extended command syntax for mesh generation
          • Fixed and Compliant base: what input motion is required?
          • Fixities and deformation boundary conditions
          • Force envelope results explained
          • Fundamentals of pseudo-static analysis in PLAXIS
          • General modeling guidelines - recommendations
          • Graphics card issues
          • Groundwater flow analysis in PLAXIS – Brief overview
          • How do I import a geometry in PLAXIS 3D?
          • How does Plaxis deal with water pressures during dynamic calculations?
          • How does Reset displacements to zero work?
          • How does the option volumetric strain work?
          • How to activate a dynamic load
          • How to change the PLAXIS model width
          • How to check undrained shear strength using Undrained A?
          • How to convert PLAXIS V21 material database to the V22 format
          • How to define and edit a material via the command line
          • How to get a load - displacement curve using SumMstage
          • How to prescribe a dynamic displacement
          • How to run a Limit Equilibrium Method analysis from PLAXIS 2D
          • How to select more than 10 nodes to be used for a curve
          • How to setup the number of steps stored in PLAXIS Input
          • How to setup tied degrees of freedom
          • How to use command log files
          • How to validate a material via the GUI and command line
          • Hydraulic conductivity input in PLAXIS using van Genuchten functional forms in a groundwater flow analysis
          • I use PLAXIS and it says I do not have the proper entitlements
          • Improving speed of mesh generation in combination with stage generation
          • In Plaxis Curves it is possible to plot Force Fx, Fy and Fz. What are these parameters?
          • Initial degree of saturation for soil activated during staged construction
          • InputSettings object in Output
          • Inspect intermediate step results in PLAXIS Output
          • Install latest 2D version and 2D AE for converting older files
          • Is it possible to apply a distributed load on tunnel lining in PLAXIS 2D?
          • Is PLAXIS 3D 64-bit?
          • Is PLAXIS 3D enabled for multicore?
          • Iterative settings: desired minimum and maximum
          • Iterative settings: Influence of Arc length control
          • Iterative settings: Max unloading steps (arc length control)
          • Key not bound to machine
          • Language reset in PLAXIS 2D and 3D
          • Launch PLAXIS 2D calculations via DOS commands
          • Load activation in time
          • Local axis and its colour indication
          • Macros using the commands runner
          • Material datasets for plates: sheet pile wall in bending
          • Materials overview in the Model explorer
          • Memory usage in dynamic calculations
          • Mesh alignment in flow problems
          • Mesh generation might not work under Windows 7 due to security settings
          • Modelling a tapered pile
          • Modelling Rock mass using discrete discontinuities vs Jointed Rock
          • Modelling soil-structure interaction: interfaces
          • Modelling technique: Vacuum consolidation
          • Modifying boundary conditions
          • Multicore CPU and 32/64-bit
          • NATM Tunneling - Beta Method: Incomplete Staged construction method vs. Deconfinement method
          • Node-to-Node anchors as an alternative for Fixed-End anchors
          • Non-consecutive order of step numbers in Plaxis
          • Obtain Object names easily to use in commands
          • Obtaining tabulated data for materials in PLAXIS Input
          • Obtaining tabulated data from PLAXIS Input
          • Obtaining time-dependent flow results at specific timestamps in a given time interval in Flow only calculations
          • On different failure criteria for soils
          • On the initialisation of the temperatures of solid elements
          • On the use of dynamic boundary conditions
          • Opening old PLAXIS project gives a popup window. What should I do?
          • Output of flow results through interfaces
          • Output project compatibility
          • Permeability in interfaces
          • Permeability in interfaces: Practical situations
          • Pile modelling in a 2D plane strain model
          • PLAXIS 2D Command compatibility notes
          • PLAXIS 3D 2013 and older PLAXIS files
          • PLAXIS 3D 2016: Fully parametric geometry
          • PLAXIS 3D Command compatibility notes
          • PLAXIS Legacy version and supported CodeMeter drivers
          • PLAXIS Output Phase/Step object compatibility
          • PLAXIS Silent Installation
          • PLAXIS Soil model numbers in command line
          • Plaxis uses SMC files for earthquakes, but what kind of format is this?
          • Points of interest for pile modelling in a 2D plane strain model
          • Problems related to non-associated plasticity
          • Program responds that drivers are out of date, but I have a newer version installed
          • Pseudo static acceleration
          • Re-use materials from other projects
          • Reduction of stiffness does not lead to a change in displacements
          • Regenerate staged construction
          • Run multiple calculations easily
          • Safety analysis and displacements
          • Safety analysis and undrained behaviour
          • Safety analysis and Updated Mesh
          • Safety calculation with a Target Value
          • Saving PLAXIS files for an older version
          • Select points for curves prior to calculation directly in Input
          • Selecting points for curves
          • Set multiple phases to be calculated
          • Showing a list of embedded beams by length
          • Small overlaps curves message in SoilTest optimisation
          • Smart selection of line elements in PLAXIS 2D Input
          • Stiffness units for structural elements in an axisymmetric model
          • Stress relaxation due to creep in concrete structures
          • Stresses in non-porous materials
          • Structural results in tables and curve plots
          • Swept meshing in PLAXIS 3D
          • Tensile behaviour in the Hoek-Brown model
          • Tension cut-off in interfaces for User Defined Soil Models
          • Time step used in dynamic calculation
          • Trim and extend a line in PLAXIS 2D
          • Tunnels in PLAXIS 3D: Extrusions and cutting planes
          • Unable to select points for curves
          • Unable to select structures or nodes
          • Use of wells in PLAXIS 3D
          • Using an accelerogram for Dynamics
          • Using partial geometry for interesting result images in PLAXIS 3D
          • Using PLAXIS Remote scripting with the Python wrapper
          • Waterlevel inspection and editing in PLAXIS 2D
          • Westergaard's added mass for hydrodynamic pressures: a simple case
          • +Working from home with PLAXIS
        • +Publications
        • +Videos - PLAXIS
      • +PLAXIS Monopile Designer
      • +PLAXIS LE
      • +SOILVISION
      • +Geotechnical SELECT Entitlements [GSE]
      • +Subscription Entitlement Service

     
     Questions about this article, topic, or product? Click here. 

    Safety analysis and undrained behaviour

    Application PLAXIS 2D
    PLAXIS 3D
    Version PLAXIS 2D
    PLAXIS 3D
    Date created 07 March 2013
    Date modified 07 March 2013

    Safety analysis in Plaxis uses a so-called phi/c reduction method in which the strength of the soil materials will be reduced with a factor ΣMsf until either failure is reached for a stable value of ΣMsf,  or the maximum number of calculation steps is reached. In case a project has one or more material sets specified as either Undrained A or Undrained B such reduction of strength may lead to a change of excess pore pressures in the model. This change of excess pore pressures can be prevented by selecting the option “Ignore undrained behaviour” for the Safety analysis phase. In this case the excess pore pressures already present at the beginning of the Safety analysis phase will remain, but no change of excess pore pressures will occur during the Safety analysis.

    A point of discussion can be whether excess pore pressures should be generated during a Safety analysis or not. Unfortunately, no straightforward answer can be given to this problem as one cannot compare with what would happen in reality as safety analysis through strength reduction is a non-physical process. In order to choose whether excess pore pressures should be allowed to change during Safety analysis the following aspects can be taken into account:

    • For loading problems (for instance embankments) allowing excess pore pressures to change often leads to an increase of excess pore pressures. This would therefore lead to a lower factor of safety compared to the case where no change of excess pore pressures would be allowed.
    • For unloading problems (for instance excavations) allowing excess pore pressures to change often leads to a decrease of excess pore pressures and sometimes even to pore tensions (suction). This would therefore lead to a higher factor of safety compared to the case where no change of excess pore pressures would be allowed.

    Based on the aspects above one could choose to use or not use the option “Ignore undrained behaviour” such that the lowest factor of safety is obtained, hence the most conservative solution.
    Another argument heard is to never allow change of excess pore pressures because the factor of safety should be determined from a specific situation with specific (fixed) excess pore pressures. In other words, the factor of safety should be determined from a “snapshot” situation in the design and analysis process and therefore the excess pore pressures should remain constant during Safety analysis being the excess pore pressures resulting from the project analysis.

    In the end the choice for using the option “Ignore undrained behaviour” in a Safety analysis is something for the user to decide. However, it may also be there is a recommendation with respect to the use of the option “Ignore undrained behaviour” in for instance the local building code.

    See also

    Safety analysis and displacements

    [Tips and Tricks]


    Safety calculation with a Target Value

    [Tips and Tricks]


    Safety analysis and Updated Mesh

    [Tips and Tricks]


    After a consolidation analysis I have excess pore pressures in "drained" material sets. Why?

    [Tips and Tricks]

    • safety analysis
    • undrained
    • PLAXIS 3D
    • factor of safety
    • PLAXIS
    • undrained behaviour
    • PLAXIS 2D
    • Share
    • History
    • More
    • Cancel
    • Micha van der Sloot Created by Bentley Colleague Micha van der Sloot
    • When: Mon, Dec 23 2019 7:10 AM
    • Micha van der Sloot Last revision by Bentley Colleague Micha van der Sloot
    • When: Tue, Dec 24 2019 6:14 AM
    • Revisions: 2
    • Comments: 0
    Recommended
    Related
    Communities
    • Home
    • Getting Started
    • Community Central
    • Products
    • Support
    • Secure File Upload
    • Feedback
    Support and Services
    • Home
    • Product Support
    • Downloads
    • Subscription Services Portal
    Training and Learning
    • Home
    • About Bentley Institute
    • My Learning History
    • Reference Books
    Social Media
    •    LinkedIn
    •    Facebook
    •    Twitter
    •    YouTube
    •    RSS Feed
    •    Email

    © 2023 Bentley Systems, Incorporated  |  Contact Us  |  Privacy |  Terms of Use  |  Cookies