Bentley Communities
Bentley Communities
  • Site
  • User
  • Site
  • Search
  • User
  • Welcome
  • Products
  • Support
  • About
  • More
  • Cancel
GeoStudio | PLAXIS
  • Product Communities
GeoStudio | PLAXIS
GeoStudio | PLAXIS Wiki Hydraulic conductivity input in PLAXIS using van Genuchten functional forms in a groundwater flow analysis
    • 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. 

    Hydraulic conductivity input in PLAXIS using van Genuchten functional forms in a groundwater flow analysis

    Application PLAXIS 2D
    PLAXIS 3D
    Version PLAXIS 2D CONNECT Edition
    PLAXIS 3D CONNECT Edition 
    Original Author Faseel Khan - Technical Support Group
    Date created 02 November 2022
    Date modified 02 November 2022

    The soil-water characteristic curve relates suction to saturation (S), volumetric water content (θ) and hydraulic conductivity (k) and the corresponding functional forms are θ(Ψ), k(Ψ) and S(Ψ) respectively. In PLAXIS, the van Genuchten functional forms S(Ψ) and k(Ψ) can be entered in every soil/rock material data set in two ways. One way to generate these functional forms is to directly input the van Genuchten parameters and the second way is to use a Spline function to fit smooth curves to tabulated data. The van Genuchten parameters or the Spline function for any soil is input in the Groundwater tab of the Material properties and selecting User-defined for the data set.

    To get parameters which are suitable for input in PLAXIS a step-wise procedure is provided to input the van Genuchten functional forms for direct input or as a spline function. The procedure converts the functional form θ(Ψ) and k(Ψ) to the functional form S(Ψ) and krel(Ψ) or vice versa.

    Often within the realm of geotechnical analysis, it is required to convert measured data concerning the degree of saturation to volumetric water content (or vice versa) for its use in either Finite Element or Limit Equilibrium Analysis in PLAXIS or SEEP/W or PLAXIS LE. To interconvert between the functional forms we need to understand porosity and its relationship with the degree of saturation. The relationship between the degree of saturation and volumetric water content is defined by the following equation:

    θ = S ƞ

    where S is the degree of saturation, ƞ is the soil porosity and θ is the volumetric water content.

    If we know S at any suction value and we know ƞ, we can then calculate θ. If ƞ remains constant throughout a transient analysis, we can convert saturation to volumetric water content at any suction value. This is because in a flow-only transient analysis the porosity does not change as described below.

    The following phase diagram shows the different phases in a soil. Fig 1a shows an unsaturated soil comprising three phases which are soil solids, water and air.
    The volume of soil solids, water and air are denoted by Vs, Vw and Va, respectively.
    The total volume Vt = Va + Vw + Vs.
    Volume of voids Vv = Va + Vw.

    On the other hand, Fig 1b shows the phase diagram for a fully saturated soil in which there are only two phases of water and soil solids because the volume of air gets filled by water.

    Porosity is defined as (Va+Vw )/Vtotal

    In a flow-only transient analysis, the volume of voids remains the same at any point in time and hence the porosity remains the same whether the soil is unsaturated or saturated as seen in both Fig 1a and Fig 1b.

    1. Van Genuchten parameters

    The closed-form relationship for the van Genuchten functional form θ(Ψ) is given by the following equation: 

    where θres is the residual volumetric water content, θsat is the saturated volumetric water content.
    α', n and m are curve-fitting parameters.
    α' is the reciprocal of the air-entry value with units of 1/kPa
    n controls the shape of the θ(Ψ) plot after the air-entry value.
    m = 1-1/n

    Similarly, the closed-form relationship for the functional form k(Ψ) is given by the following equation:

    where ksat is the saturated hydraulic conductivity.

    The input fitting parameters for the functional form S(Ψ) and krel(Ψ) are ga, gn, gc, gl and krel and ksat which are explained below.

    The closed-form relationships for the functional forms S(Ψ) and krel(Ψ) are given below:

    where Sres is the residual degree of saturation, Ssat is the saturated degree of saturation and krel is the relative hydraulic conductivity.
    ga is reciprocal of air-entry value similar to α' with units of 1/m so its value is determined by dividing α' by the unit weight of water.
    gn controls the shape of the S(Ψ) plot after the air-entry value so gn = n.
    gc = 1- 1/gn 
    gl is a fitting parameter controlling the shape of the krel(Ψ) plot and affects the effective degree of saturation Seff and can be taken as 0 for some soils.

    Based on the relationships provided above, the van Genuchten’s parameters can be interconverted from the functional form k(Ψ) and θ(Ψ) to the functional form S(Ψ) and krel(Ψ) and vice versa.

    2. Spline function

    The Spline function requires direct input of the capillary height Ψ, relative hydraulic conductivity krel, and the degree of saturation which are all positive values. Data for the Spline function can be entered in the PLAXIS Groundwater tab of the Material properties and selecting User-defined for the data set and then selecting Spline for the Model.  

    2.1 Converting the functional form k(Ψ) and θ(Ψ) to krel(Ψ) and S(Ψ) 

    1. Note the values for θres and θsat.
    2. Use θ = S η to determine, porosity then Sres and Ssat. Porosity remains constant in a flow-only analysis
    3. Get krel using krel= k/ksat for each data point from the k(Ψ) plot
    4. Get data points from k(Ψ) and θ(Ψ) plots
    5. Convert suction pressure to suction head by dividing with the unit weight of water
    6. Get the degree of saturation using θ = S η against the data points for θ

    This gives the data for spline fit in the functional forms S(Ψ) and krel(Ψ)

    Note: If the suction head data points for the k(Ψ) and θ(Ψ) plots do not coincide then manually read the S values at the suction values corresponding to the k(Ψ) data points.

    2.2 Converting the functional form S(Ψ) and krel(Ψ) to θ(Ψ) and k(Ψ)   

    1. Note the values for Sres and Ssat.
    2. Use θ = S η to determine, porosity then θres and θsat. Porosity remains constant in a flow-only analysis
    3. Get krel using krel= k/ksat for each data point from the krel(Ψ) plot
    4. Get data points from krel(Ψ) and S(Ψ) plots
    5. Convert suction head to suction pressure by multiplying with the unit weight of water
    6. Get volumetric water content using θ = S η against the data points for S

    This gives the data for spline fit in the functional forms θ(Ψ) and k(Ψ)

    Note: If the suction head data points for the krel(Ψ) and S(Ψ) plots do not coincide then manually read the θ values at the suction values corresponding to the krel(Ψ) data points.

    • PLAXIS 3D
    • material set
    • flow parameters
    • Groundwater
    • PLAXIS
    • material
    • PLAXIS 2D
    • Groundwater flow
    • Share
    • History
    • More
    • Cancel
    • Stefanos Papavasileiou Created by Bentley Colleague Stefanos Papavasileiou
    • When: Wed, Nov 2 2022 11:36 AM
    • Faseel Khan Last revision by Bentley Colleague Faseel Khan
    • When: Wed, Nov 2 2022 12:11 PM
    • Revisions: 3
    • 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