My force envelope distribution value is larger  than any of the phases' results: How can this be?

In PLAXIS 2D, sometimes, the maximum or minimum values displayed on the force distribution envelope can be larger  than any of the phases’ results.  This can be explained by the fact that these maximum and/or minimum values for the axial force N, the shear force Q or the bending moment M were recorded at an (unknown) intermediate calculation step.

Due to the non-linear behaviour of the soil, each calculation phase is generally divided into a number of calculation steps. In order words, the external loading (Out-of-Balance) is applied and solved in (small) increments.

Each calculation steps is, during the calculation, temporarily saved in the Windows TEMP folder, in a file named data.### (### corresponds to the calculation step number). During a calculation step, the actual forces are compared with the ones from subsequent calculation steps and the maximum and minimum variables are updated if the actual force is bigger or lower than the maximum or minimum values recorded in previous calculation steps, respectively.

The force envelope distribution is the visual representation of the maximum and minimum force values recorded during calculation and it doesn’t necessarily mean that these occurred in the last calculation step of any phase. In other words, whenever a force envelope distribution value is larger than in any of the phases' final results, this is an indication that the maximum and minimum force values occurred in an intermediate calculation step.

However, by default, a calculation phase has the Max number of steps stored (in the numerical control parameters settings in the Phases window) set to 1, so only the phase’s last calculation step file will be stored and saved in the project folder. As a consequence, if the maximum and minimum force’s values occurred in an (unknown) intermediate calculation step, the user won’t be able to visualise the calculation results for that specific intermediate calculation step.

Find the calculation step when a force envelope value has been reached and visualize its results

In order to find out in which (intermediate) calculation step the maximum/minimum value occurred, you need to:

1. Store all intermediate calculation steps, during the calculation ( Max number of steps stored = Max steps value on each Phase's numerical control parameters tab)
2. Run your model and save it at the end of the calculation
3. Select to view the results for the plate in Output and then click the Select points for curves button to choose the plate’s post-calc node you wish to retrieve the results for.
4. Create a Step vs post-calc node force's curve, in the Curve manager window. In the generated curve, you can now see the force evolution during calculation and identify in which calculation step the maximum/minimum value occurred.
5. Knowing the calculation step number, you can change the plot of the force distribution to the step in which the maximum or the minimum value was recorded. For that, just make sure that the button in front of the drop-down menu is set to show all saved calculations steps results, as shown in the image below.  From there, you can visualize any calculation steps results.

This movie demonstrates how to set-up a model to predict the development of seepage around a pressure tunnel, where the groundwater table is situated far below the pressure tunnel. Full validation of the model against the analytic solution can be found in the document linked below.

In the material data base of Plates in PLAXIS 2D and 3D there is the option to select ‘End bearing’. Selecting this option may be appropriate to provide some sort of vertical end bearing (tip resistance) in the case the plate is used as a wall.

In reality, vertical loads on walls, for example as a result of vertical components of anchor forces or point loads on the wall, are sustained by the shaft friction and the tip resistance. A certain amount of resistance is offered by the soil under the tip, depending on the thickness or the cross section area of the tip. Slender walls are often modelled as plates. Due to the zero thickness of the plate elements, vertical plates (walls) have no end bearing. The effects of end bearing can still be considered in the calculation when the corresponding option is selected in the material data set. In order to consider end bearing at the bottom (tip) of plates, a zone in the soil volume elements surrounding the tip of the plate is identified where any kind of soil plasticity is excluded (elastic zone). The size of this elastic zone is determined as D_eq = √(12 EI / EA).

Notes

• In contrast to embedded beam elements, it is NOT the idea that this end bearing represents the true end bearing capacity of the wall. It just prevents unrealistic vertical movement or penetration of the wall into deeper layers. The value of end bearing cannot be prescribed by the user, and it is neither theoretically determined by PLAXIS.
• Note that sheet pile walls have very little end bearing, considering that the thickness of the steel is much less than D_eq, when modelling them as plates. Hence, the end bearing option shall NOT be used for sheet pile walls.

For more background on the End bearing option, please refer to the PLAXIS 2D and 3D Reference Manual and Material Models manuals.

It is observed in simulations of excavation projects using the Hardening Soil model (or HS small model) that the soil below the bottom of the excavation behaves less stiff than in reality. The reason is that the stiffness of soil is stress dependent and excavation releases the stress on top, however, in reality the stiffness will not reduce so much due to the pre-consolidation stress. Therefore, in the GHS model (generalized hardening soil model) the stress dependency formulation of the Hardening Soil small model has been altered in order to account for the pre-consolidation stress. The Generalized Hardening Soil model (GHS) is a more modular version of the original Hardening Soil small model. It has several switches which allow the users to change the configurations of strain and stress dependency.

In order to obtain the model, send your request to sales@plaxis.com. Support on the use of the generalized hardening soil model is only provided for this DLL under the conditions of the PLAXIS VIP support service and Article 10 of the End-User Licence Agreement.

Status May 2016

Known issue ID: 5362

In the implementation for the Generalized Hardening Soil (GHS) model version 2014.223.0.0 (March 2014) the internal parameter determination is only stored for one material dataset at the beginning of a calculation phase. This means that when having more than one material dataset using the Generalized Hardening Soil model, these internal parameters for the stiffness behaviour will only use the parameters from one material dataset, and this gives incorrect behaviour for all the other material datasets using the GHS model.

We are working on a solution for this. For the time being, users are strongly advised not to define more than one GHS material dataset in the model until we release the fixed user defined soil model files.

This document verifies that groundwater flow principles are correctly implemented in PLAXIS. The purpose of this example is to determine the length of the seepage face l in an inclined river bank with slope a . The problem geometry is presented below. Assuming a point P on the phreatic surface, with known location determined by length L and height H, the seepage face l and the phreatic surface are found through a set of nonlinear equations.

Used version:

• PLAXIS 2D - Version 2015.02 - PlaxFlow module
• PLAXIS 3D - Anniversary Edition (AE.01) - PlaxFlow module

This requires a PlaxFlow module for groundwater flow

This document describes an example that is used to verify the elastic deformation capabilities of PLAXIS. The settlement and stress distribution within a semi-infinite, homogeneous and isotropic soil mass with linear stress-strain relationship, under circular uniform pressure, is studied. PLAXIS results are compared with the analytical solution presented by Boussinesq (1885).

3D geometry for the Boussinesq problem

Used version:

• PLAXIS 2D - Version 2015.02
• PLAXIS 3D - Anniversary Edition (AE.01)

This document verifies that the non-linear deformation of plates is treated correctly in PLAXIS. An elastoplastic 'M - k' material type is used and the deformation of a cantilever under various loading conditions is studied.

Used version:

• PLAXIS 2D - Version 2015.02

This document verifies that the undrained analysis of partially saturated soil is correctly implemented in PLAXIS. Bishop's effective stress (Bishop & Blight, 1963) is used in PLAXIS to handle unsaturated soil conditions. In undrained analysis, excess water pore pressures are generated based on the water bulk modulus, the value of which depends on the Soil Water Characteristic Curve (SWCC), i.e. the relationship between the degree of saturation and the applied suction. It is attempted to show how the SWCC affects the undrained behaviour of soil.

Used version:

• PLAXIS 2D - Version 2015.02
• PLAXIS 3D - Anniversary Edition (AE.01)

This document verifies that groundwater flow principles are correctly implemented in PLAXIS. Bishop's effective stress (Bishop & Blight, 1963) is used in PLAXIS to handle unsaturated soil conditions. An example is used to verify the capability of PLAXIS to calculate Bishop's effective stress.

3D Geometry for the verification of Bishop's effective stress

Used version:

• PLAXIS 2D - Version 2015.02
• PLAXIS 3D - Anniversary Edition (AE.01)

This document verifies that groundwater flow principles are correctly implemented in PLAXIS. A soil column with a drain inside is simulated. The total amount of water leaving through the drain is calculated in PLAXIS and the numerical results are compared to the closed form solution proposed by Dupuit (1863).

Used version:

• PLAXIS 2D - Version 2015.02 - PlaxFlow module
• PLAXIS 3D - Anniversary Edition (AE.01) - PlaxFlow module

This requires a PlaxFlow module for groundwater flow

This document verifies that groundwater flow principles are correctly implemented in PLAXIS. A soil column with a well inside is simulated. Under constant infiltration conditions, the total discharge from the top soil boundary is calculated in PLAXIS.

Used version:

• PLAXIS 2D - Version 2015.02 - PlaxFlow module
• PLAXIS 3D - Anniversary Edition (AE.01) - PlaxFlow module

This requires a PlaxFlow module for groundwater flow

With the combination of the startup command line parameters to launch PLAXIS and the commands runner in PLAXIS 2D and PLAXIS 3D, it is relatively easy to make a setup in order to run multiple calculations unattended.

PLAXIS 2D

Since PLAXIS 2D AE, the program also the command line and the commands runner.
To run a serie of commands (stored in a command log file) after loading a PLAXIS 2D project (extension *.p2dx), the format of the command line for the Windows Console is:

"[PLAXIS 2D installation folder]\Plaxis2DXInput.exe""[full path to Plaxis file]""--run=[path to command file]"

Example:

"C:\Program Files (x86)\Plaxis\Plaxis 2D\Plaxis2DxInput.exe""D:\Projects\Project1A.p2dx""--run=D:\Projects\calculateprojects.log"

PLAXIS 3D

In order to launch a command file after loading a PLAXIS 3D project, the format of the command line is similar:

"[PLAXIS 3D installation folder]\Plaxis3DInput.exe""[full path to Plaxis file]""--run=[path to command file]"

Example:

"C:\Program Files (x86)\Plaxis\Plaxis 3D\Plaxis3DInput.exe""D:\Projects\Project1A.p3d""--run=D:\Projects\calculateprojects.p3dlog"

Setting up multiple calculations

If you want to calculate multiple projects directly after each other, the simplest way to do this, is to use such a commands log file and use a Batch-file (.bat) to run several calculations.

Commands log file

The commands log file will contain all the commands that will be run after loading the model. In this case, we will create this file ‘calculateprojects.log’, an ASCII file you can make with e.g. Notepad. It will contain the following instructions:

1. go to the staged construction mode
2. calculate all phases, not taking into account its state
3. save the file once the calculation is done
4. and close Plaxis, so we can run the next calculation

The commands that we need to store in this command log file ‘calculateprojects.log’ are:

gotostagescalculateTruesave__kill

Note: if one of the commands in this do not work (e.g. when there is no mesh defined, the calculation cannot start and the program shows an error message), then the entire process is halted.

Executing multiple calculations

In order to launch an application, we can take advantage of the Windows shell. For this we will use a BAT-file (you can edit this with any text editor, like Notepad). Make sure to give the file the extension .BAT

The content of this file to run four PLAXIS 2D calculations on these files stored in the folder D:\Projects is:

set Plaxis="C:\Program Files (x86)\Plaxis\Plaxis 2D\Plaxis2DxInput.exe"

%Plaxis% "D:\Projects\Project1A.p2dx""--run=D:\Projects\calculateprojects.log"
%Plaxis% "D:\Projects\Project1B.p2dx""--run=D:\Projects\calculateprojects.log"
%Plaxis% "D:\Projects\Project1C.p2dx""--run=D:\Projects\calculateprojects.log"
%Plaxis% "D:\Projects\Project1D.p2dx""--run=D:\Projects\calculateprojects.log"PAUSE

Now we can just double click on the BAT-file to run all these calculations.

For a demonstration, please see our animation: Using a batch file to run commands

Note, this is a VIP feature: a licence with the VIP add-on is required to run the commands runner

This document verifies that groundwater flow principles are correctly implemented in PLAXIS. Assuming an horizontal confined aquifer, the radial flow towards a well is studied under transient and steady-state flow conditions. PLAXIS results are compared with the analytical solutions presented by Theis (1935) and Thiem (1906).

Used version:

• PLAXIS 2D - Version 2015.02 - PlaxFlow module
• PLAXIS 3D - Anniversary Edition (AE.01) - PlaxFlow module

This requires a PlaxFlow module for groundwater flow

This document verifies that groundwater flow principles are correctly implemented in PLAXIS. Poroelasticity theory, first introduced by Biot (1941), counts for coupled hydro-mechanical processes. The presented verification example studies the case of a drilled vertical borehole in saturated soil formation (porous rock), subjected to non-hydrostatic in situ stress. PLAXIS results are compared to the analytical solution provided by Detournay & Cheng (1988).

Used version:

• PLAXIS 2D - Version 2015.02
• PLAXIS 3D - Anniversary Edition (AE.01)

This requires a PlaxFlow module for groundwater flow

Due to adding more features and improving the program’s data structure for stability and performance, the data structure of the PLAXIS data files has evolved over time.

PLAXIS 2D 2016

PLAXIS 2D 2016 can only read PLAXIS *.p2dx files created with PLAXIS 2D 2016, PLAXIS 2D 2015 or PLAXIS 2D AE.

Tip: The procedure of keeping both versions of 2D AE and 2D 2015 installed in the same computer for the conversion of older files is described in the related article on how to Install latest 2D version and 2D AE for converting old files.

PLAXIS 2D 2015

PLAXIS 2D 2015 can only read PLAXIS *.p2dx files created with PLAXIS 2D 2015 or PLAXIS 2D AE.

PLAXIS 2D 2015 cannot use the 2D Classic to 2D AE converter to convert older Plaxis *.P2D files into the data format needed for PLAXIS 2D 2015. In order to use *.P2D files (2D Classic and earlier) in PLAXIS 2D 2015, these files first need to be converted to the PLAXIS 2D AE format using a PLAXIS 2D AE installation in combination with the 2D Classic to 2D AE converter installation, see below.
After this, you can open these 2D AE files in PLAXIS 2D 2015.

Tip: The procedure of keeping both versions of 2D AE and 2D 2015 installed in the same computer is described in the related article of how to Install latest 2D version and 2D AE for converting old files.

PLAXIS 2D AE

With PLAXIS 2D AE, the file extension was changed from *.P2D to *.p2dx. PLAXIS 2D AE can only read files made with PLAXIS 2D AE (*.p2dx). Plaxis project files created with the PLAXIS 2D 2012 version or earlier (with extension .P2D) cannot be opened directly in PLAXIS 2D AE: they first need to be converted using the 2D Classic to 2D AE converter.

The 2D Classic to 2D AE converter is an add-on program for PLAXIS 2D AE. In PLAXIS 2D AE when opening a 2D classic file (*.P2D) this converter program will be called, and it will transform the old PLAXIS 2D project via 2D AE's command line into the new format. Note that this Converter is intended to only work directly from PLAXIS 2D AE, and it is not intended to start the Converter manually. Please follow these steps to convert the older PLAXIS data to the new version:

• Start PLAXIS 2D AE Input
• Select Open an existing file
• Go to the location of the old file
• Select the file type PLAXIS 2D files (*.p2d) from the drop down item in the lower right corner:
• And then select your PLAXIS 2D Classic file and click Open
• Make sure to read the conversion notes about changed options in the program
• Then click OK, and the PLAXIS 2D AE model will be built up using the Commands Runner (Note that this requires a PLAXIS VIP licence/subscription)

Please note that in order to perform all the above mentioned procedures, you need to have the PLAXIS 2D Classic to 2D AE converter installed. This tool comes with the full setup of PLAXIS 2D AE as an option during the installation procedure of the PLAXIS software. Next to this, it is also available as a separate program via PLAXIS Connect.

For older PLAXIS files (PLAXIS 2D V8 and V9): these files first need to be converted to PLAXIS 2D Classic before it can be converted into the 2D AE data format, see below or the related page:
Conversion from 2D Version 8/9

PLAXIS 2D 2010 - 2011 - 2012 - Classic

With PLAXIS 2D 2010, the file extension was changed from *.PLX to *.P2D. PLAXIS 2D 2010 to PLAXIS 2D Classic was capable of reading in files created with earlier versions starting from Version 8.2 (with extension *.plx).
To convert PLAXIS 2D V8/V9 files, it is recommended to use PLAXIS 2D Classic.

PLAXIS 2D Version 9

PLAXIS 2D Version 9 can read *.PLX files made with PLAXIS 2D Version 8 and PLAXIS 2D Version 9.

PLAXIS 2D Version 8

PLAXIS 2D Version 8 was the only program available that could convert PLAXIS 2D Version 7 files into the newer file structure for the *.PLX file.

PLAXIS 3D allows to import volumes and surfaces. On top of that, you can also import the top and bottom soil surfaces in the Modify Soil Layers configuration window in the Surfaces tab.
When importing a geometry file, a list of possible file extensions are shown. Most common import file types are:

• STEP/STP: "Standard for the Exchange of Product model data" files
• brep: Open CASCADE BRep file format
• DWG/DXF *): For DWG and DXF files we only support 3DFACE entities (i.e. triangulated surfaces/volume boundaries, not quads. Update: since PLAXIS 3D2011, 3DFACE quads are also supported), other entity types are ignored. Hint: you can also try to export to 3ds and import that into PLAXIS 3D which succeeds more often.
• 3DS *): valid surfaces or volumes need to be defined

*): with the internal changes for the geometric datamodel for the next version (3D 2016), Plaxis will no longer support the import of triangulated geometry. This includes *.3ds, *.dwg and triangulated*.dxf files.

Importing DXF created with AutoCad Civil 3D
Please see a demonstration movies in the related items:

• Importing a surface from AutoCAD 3D Civil
• Importing volumes

Importing 3DS files from Google's Sketchup Pro
Not supported starting PLAXIS 3D 2016

Google's SketchUp is a tool for creating, editing and sharing 3D models. SketchUp Pro exports your data as 1:1. When importing objects in PLAXIS 3D, these are taken as the project units. When importing a Sketchup model with the project units set to inch, into a PLAXIS 3D model with meters as project length units, you will need to scale the model in order to get the same model size.

Google SketchUp Pro can export models as 3DS-files, that can be imported into PLAXIS 3D. In order to get the best options for 3ds-files from Sketchup, use these settings (based on Google Sketchup Pro 6):

1. select the desired geometry
2. intersect the desired geometry with itself (via Edit menu)
3. then export the selection as a 3DS-file
4. and make sure you apply these settings (under Options):export as single object, export entire model, or only the selection, do NOT export two-sides faces, do NOT export stand alone edges, since PLAXIS 3D does not support materials and cameras, do NOT export these, and choose your scale
5. save the file
6. now import the file into PLAXIS 3D as a surface or as a solid

Note: with the release of PLAXIS 3D 2016 and PLAXIS 2D 2017, Plaxis will only support 64 bit user defined DLL files. 32 bit DLL files will not be loaded by the Plaxis programs with these versions.

PLAXIS has a facility for user-defined (UD) soil models. This facility allows users to implement a wide range of constitutive soil models (stress-strain-time relationship) in PLAXIS. Such models must be programmed in FORTRAN (or another programming language), then compiled as a Dynamic Link Library (DLL) and then added to the PLAXIS program directory.

In principle the user provides information about the current stresses and state variables and PLAXIS provides information about the previous ones and also the strain and time increments. In the material data base of the PLAXIS input program, the required model parameters can be entered in the material data sets.

For more details, please read the attached document and example code.

Location

In PLAXIS 2D 2012, PLAXIS 2D Classic and earlier and in PLAXIS 3D 2012 and earlier, the user-defined soil model's DLL files should be placed in the program's installation folder, e.g.

• PLAXIS 2D: C:\Program Files\Plaxis\Plaxis 2D\
• PLAXIS 3D: C:\Program Files\Plaxis\Plaxis 3D\

Since PLAXIS 3D 2013 and PLAXIS 2D AE, these user-defined soil model's DLL files should be placed in a subfolder called udsm:

• PLAXIS 2D: C:\Program Files\Plaxis\Plaxis 2D\udsm\
• PLAXIS 3D: C:\Program Files\Plaxis\Plaxis 3D\udsm\

Diclaimer: the PLAXIS organization cannot be held responsible for any malfunctioning or wrong results due to the implementation and/or use of user-defined soil models.

Note: with the release of PLAXIS 3D 2016 and PLAXIS 2D 2017, Plaxis will only support 64 bit user defined DLL files. 32 bit DLL files will not be loaded by the Plaxis programs with these versions.

In order to use a User Defined Soil Model (UDSM) with the 64-bit calculation kernel you must have a 32-bit version and a 64-bit version of your user defined soil model

• Applications that are compiled as 32-bit applications cannot communicate with 64-bit DLL files. Currently, the Plaxis GUI is still only available as a 32-bit application.
• 64-bit applications (like the calculation kernel) cannot cannot communicate with 32-bit DLL files. These 32 bit DLL files are needed for the input of the UDSM’s material parameters in the Input program.

When using the Plaxis 2D/3D 64-bit calculation kernel in combination with a User Defined Soil Model (UDSM) DLL-file, you should compile your UDSM as a 64-bit DLL-file. When doing this, this newly compiled 64-bit DLL cannot communicate with the 32 bit GUI of the Plaxis Input program to setup your material parameters, so you will need both.
For this reason, please do the following:

• compile the UDSM as a 32-bit DLL-file, e.g. YourModel.dll
• compile the UDSM also as a 64-bit DLL-file, but give it the same name as your 32-bit DLL file with 64 added to the name, e.g. YourModel64.dll.

Note that you should really compile it as 32-bit and 64-bit, and not just rename it.
If all is compiled correctly, and the names are set correct, then you can use the UDSM in the 32-bit GUI and in the 64-bit calculation kernel.

32 bit UDSM DLL

This will no longer be supported starting PLAXIS 3D 2016 and PLAXIS 2D 2017

If you only have a 32 bit User Defined Soil model DLL file, you can also just use the 32-bit calculation kernel by disabling the 64-bit calculation kernel. The easiest way to do so, is to rename the 64-bit calculation kernel to something else and then the calculation will automatically fall back to the 32 bit-calculation kernel.

PLAXIS 2D 2011, 2012 and 2D Classic

Since PLAXIS 2D 2011.01, a 64 bit calculation is available. In order to disable the use of the 64 bit calculation kernel to allow for usage of 32 bit User Defined Soil Models, go to the PLAXIS installation folder and search for the file "plasw64.exe". Then rename this file to e.g. "_plasw64-backup.exe"
Now you should be able to use the Plaxis 32 bit calculation kernel together with the 32 bit User Defined Soil Model dll.
In experience you do not loose much calculation speed, and only when you go over 10,000 15-noded elements the memory usage could be an issue. For most practical cases in PLAXIS 2D this is not a limitation.

PLAXIS 2D AE, 2D 2015 and later

Since PLAXIS 2D AE, the 64 bit kernel is not located in the PLAXIS installation folder, but in a subfolder called 64. Here the same trick can be applied by renaming the calculation kernel from "plasw64.exe" to e.g. "_plasw64-backup.exe"

PLAXIS 3D

For Plaxis 3D, the 64-bit calculation kernel is called plasw364.exe. To fall back to the 32-bit calculation kernel (and to use that with the 32 bit User Defined Soil Model), you can e.g. rename the file to plasw364_disabled.exe. To restore the 64-bit behaviour, you can just rename the file back to plasw364.exe or use Plaxis Connect to restore the original files.

Since PLAXIS 3D 2013, the 64 bit files are located in the 64 bit subfolder of the PLAXIS installation folder.