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

Description

A small Python script was written to obtain deformation results using the Remote scripting features in the PLAXIS 3D AE Output program. The results are retrieved using Output’s getsingleresult command for a set of coordinates written in a text file. The retrieved results are stored in a separate text file.

This Python script was written for PLAXIS 3D AE in combination with Python 3.4.x

Instructions

1. Make sure PLAXIS 3D Output is running with a VIP licence;
2. Write a text file with points' coordinates to retrieve the data for;
3. Launch the Remote server on PLAXIS 3D Output on port 10001 (look for outputport variable);
4. Run the Python script to retrieve the deformations;
5. Point to the correct text file for the points' coordinates;
6. The results are then stored in a text file with this content per line:
     phasename  pointname  ux  uy  uz  
7. This text file is ready to copy & paste to Microsoft Excel or any other spreadsheet program

Developer

Filippo Forlani

Contact

Filippo Forlani
SGAI srl, ITALY
www.sgai.net
email: filfor @ gmail.com
Twitter @FilippoForlani

Licence

This Python script is licenced under GNU GPL 3.0

Disclaimer: This Python script is made available as a service to Plaxis users to be used in combination with a VIP licence. However, Plaxis does not accept any responsibility when using this Python script in combination with Plaxis. Hence, the user needs to validate results obtained from this script by him/herself. Plaxis does not provide support on the use of this Python script.

Fixed-End (FE) anchors are single point spring elements that can be used to model anchors, struts and other types of ‘flexible’ supports. PLAXIS 2D and 3D allow for only one FE anchor per geometry point. However, in some situations, it may be required to fix a structure in different directions using spring supports, such as indicated in the figure below.

This would require two or more FE anchors to be applied at the same geometry point, which is currently not possible.

The way to overcome this limitation is to use None-to-Node (N2N) anchors instead of FE anchors. N2N anchors form a spring connection between two geometry points. However, the second point may also be a fixed point at the model (bottom) boundary, which makes that the N2N anchor basically works as an FE anchor.

In the above example case, the vertical FE anchor could be replaced by a vertical N2N anchor with its lowest point connected to the bottom boundary.

Now, there are three issues to consider:

1. The direction of an FE anchor can be defined as an anchor property, whereas the direction of a N2N anchor is just its orientation in the geometry model. The spring support is in this direction. Considering that the bottom boundary is used for the fixed point, the replacement of an FE anchor by an N2N anchor works best for a (primarily) vertical support.
2. The equivalent length of an FE anchor can be defined as an anchor property, whereas the equivalent length of an N2N anchor is the distance between the two geometry points to which the anchor is connected. Since the distance between the point to be supported and the model boundary may be different than the desired equivalent length, a ‘scaling factor’ needs to be applied on the anchor stiffness in the corresponding material data set. For example, if the equivalent length is supposed to be 5 m and the length of the N2N anchor to the bottom of the model is 10 m, then the axial stiffness EA in the material data set must be set twice as high as the actual stiffness. Alternatively, the anchor spacing may be decreased by a factor 2, which has the same scaling effect.
3. Make sure that the boundary to which the N2N anchor is connected is active in all calculation phases in which the anchor is supposed to be active. For the bottom boundary this is generally the case, but note that if for some reason, the part of the boundary where the fixed point is attached is de-activated, the N2N anchor will automatically be de-activated as well.

Vacuum consolidation is a technique to apply preloading on a construction site by creating an 'under-pressure' in the ground and thus using the external atmospheric pressure as preloading. In this way, the stability of the sub-soil is increased and settlements during and after the construction are reduced. This technique is usually applied on near-saturated soils with a high water table. This article explains the details of modelling vacuum consolidation in PLAXIS.

There are various methods of vacuum consolidation in the real world, but they are all modelled in a similar way in PLAXIS. Most methods in reality are using vertical drains, which are somehow connected at the top to an air pump that reduces the air pressure in the drains until a near-vacuum exists. In practice, a complete vacuum (100 kN/m2 pressure) is not achievable, but an effective under-pressure of 60 - 90 kN/m².

Since PLAXIS does not take air pressure into account (atmospheric pressure is assumed to be the zero reference pressure level), a reduction of the groundwater head is used instead to simulate vacuum consolidation. This means that the way vacuum consolidation is modelled leads to negative pore stresses (suction), which are not there in reality.

1 Vacuum consolidation in a one-dimensional soil column

In the simplified case of a one-dimensional soil column, vacuum consolidation can be modelled by performing a groundwater flow calculation or a fully coupled flow-deformation analysis with hydraulic conditions at the model boundaries such that in the vacuum area the groundwater head is prescribed at a level that is 10 m (or less) lower than the vertical coordinate of the global phreatic level. A reduction of the groundwater head of 10 m is equivalent to an under-pressure of 100 kN/m² (i.e. complete vacuum).

2 Vacuum consolidation in a 2D or 3D model

In a 2D or 3D numerical model of a realistic project, vacuum consolidation can be modelled by performing a groundwater flow calculation or a fully coupled flow-deformation analysis with vacuum drains in which the head specified in those drains is 10 m (or less) lower than the vertical coordinate of the global phreatic level. A reduction of the groundwater head of 10 m is equivalent to an under-pressure of 100 kN/m². The distance between the vacuum drains in the model is arbitrary, but should be selected such that the difference in groundwater head in the vacuum area is limited. In general, a distance between the drains less than a quarter of the drain length seems appropriate (i.e. complete vacuum).

3 Other requirements

A reduction of the groundwater head implies that the soil in the vacuum area becomes unsaturated, whilst this soil volume is supposed to be fully saturated. The user must arrange additionally that saturated conditions apply to this volume. This requires the following settings to be made in the corresponding material data sets:

• The unsaturated unit weight, γ_unsat (General tabsheet of the Material data set), must be set equal to the saturated unit weight, γ_sat.
• The hydraulic model must be set to Saturated after selecting User-defined as hydraulic data set (Model group in Groundwater tabsheet).

If these settings are not made, the unit weight of the soil will change from saturated to unsaturated as soon as the phreatic level drops as a result of the reduction of the groundwater head in the vacuum drains. Moreover, the soil permeability will reduce according to the reduced relative permeability in the unsaturated zone, depending on the selected hydraulic data set (by default Fine material). Both effects are not realistic and can be overcome by making the aforementioned changes in the corresponding material data sets.

4 Calculation options

Vacuum consolidation (using reduced groundwater head boundary conditions or reduced heads in vacuum drains) can be applied in the following calculation types:

• Plastic (select Steady-state groundwater flow as Pore pressure calculation type);
• Consolidation (select Steady-state groundwater flow as Pore pressure calculation type);
• Fully-coupled flow-deformation analysis.

This means that all input requirements for a groundwater flow calculation have to be met, i.e:

• All material data sets must have non-zero permeabilities;
• Hydraulic boundary conditions (groundwater head and closed flow boundaries, if applicable) must have been specified.

Moreover, it is required to de-select the Ignore suction option in the Deformation control parameters section of the Phases window.

Note that only vacuum drains allow a groundwater head to be specified below the actual drain level, which leads to tensile pore stresses (suction). Normal drains do not allow for suction. Also note that, if vacuum drains are used in a Consolidation calculation whilst the pore pressure calculation type is set to Phreatic, the drains will work as normal drains rather than vacuum drains. This means that they only affect the consolidation of excess pore pressures, whilst the steady-state pore pressure is fully determined by the global water level and local cluster settings.

5 Switching-off vacuum

If the vacuum is to be 'switched-off' in subsequent calculations while the drains are still supposed to be active for consolidation purposes, the corresponding head in the drains needs to be changed from the reduced head level to the original global water level. This leads to the situation that the new pressure head in the drain is higher than the groundwater head in the area around the drain. As a result, one might expect that water
will be flowing from the drain into the ground, which is an artefact of the numerical modelling of vacuum consolidation.

In order to avoid such unrealistic behaviour, PLAXIS prevents at all times water to flow from a drain into the surrounding soil, since drains are meant to drain water out of the ground rather than bring water into the ground. Hence, the aforementioned artefact will not occur in PLAXIS.

This text is taken from the PLAXIS 2D 2016 Reference Manual

Introduction

Developments for PLAXIS 3D AE and PLAXIS 3D 2016 changed the internal structure of the geometry definition. In versions prior to PLAXIS 3D AE (3D 2013, 3D 2012, and older), the internal geometry data structure was entirely based on triangles. In more complex projects, especially those with curved shapes, this created issues and limitations.
PLAXIS 3D AE is a transitional version; it is a hybrid version: parametric geometry for natively created surfaces and volumes, while triangulated geometry from boreholes and imported CAD geometry. In PLAXIS 3D 2016, however, the entire geometry is solely based on parametric geometry.

Issues with tessellated geometry

In PLAXIS 3D 2013 and older, the internal structure of the entire geometry is tessellated: all geometric surfaces and the volume sides (so called BReps or Boundary Representations) are internally made up of triangles.

Figure 1. Rectangle and soil block and their BRep triangles (right)

This works great when using basic, straight sided shapes. But in the case of curved shapes, like arcs, circles and cylinders, this tessellation leads to an approximation of these curved shapes: the straight sides of the triangles have to form the boundary of these shapes.

Of course, when defining a circular shape ideally you want to retain this shape, and not have a shape that approximates this arc. When trying to connect other geometry to these shapes, due to this approximation, this may be very challenging. You can think about connecting tunnels, side tunnels and galleries, but also combi-walls when connecting the tubular piles (cylinders) with sheet pile walls (surfaces).

Not having a fully curved shape can also have consequences on the model results, for instance, due to interface locking when such an approximated circular shape contains significant corners in the interface definition loaded under large shearing conditions.

Linked problem: Possible over-estimation of lateral circular pile bearing capacity [link]

A second issue is caused by the internal triangulation of multiple shapes that have to be intersected. This intersection takes place when we change from the geometry creation mode (Soil / Structures mode) to one of the green modes where we will work with the final geometry for meshing and calculations (Mesh / Flow conditions / Staged construction). This intersection is necessary to be able to uniquely identify parts of the entire model’s geometry, e.g., soil inside or outside an excavation, or surface loads left and right from a wall.
To ensure that the program does not incorrectly change the geometry, the original tessellation is retained. This implies that the original triangles in the tessellation will be kept, and may be subdivided into several parts for discretizing the intersected "cut objects".

See the example below of a tunnel shape (Figure 2) with a cutting planes to simulate tunnel construction stages. When zooming in the behaviour of one cutting plane with the tunnel (Figure 3), we can still recognize the original two triangles (B) in the intersection result (C).

Figure 2. Tunnel with cutting plane to simulate staged construction segments

Figure 3. Tunnel side view and cutting plane (magenta) with (internal) tessellation rendering (B,C)

When the intersection of two geometric objects is close to e.g., edges, then this can become complicated. If from the previous example the surface is very long and the cutting plane is close to the left edge of the surface, we will get a small triangle in the intersection results, see Figure 4 below:

Figure 4. Long tunnel side face and cutting plane with (internal) tessellation rendering

When the dimensions of such small triangles are below the geometrical tolerances used in the PLAXIS 3D program, these small triangles will be considered to be obsolete, and will be filtered out of the geometry, which will lead to failing intersection actions.

Linked problem: Tunnels in PLAXIS 3D: Extrusions and cutting planes [link]

Solution: Parametric geometry

Approximating real 3D curves shaped using tessellated geometry gives problems in some cases, as explained above. In order to solve these issues related to approximation and discretization, we worked hard on implementing a geometric data structure based on mathematical modelling of shapes and objects, i.e. an arc is an arc, not an approximation. Since the geometry is now based on mathematical equations using parameters to describe geometry, e.g., radius and centre point for an arc, we refer to this as parametric geometry.

With this parametric geometry, we now also have true intersections of the true shapes: we do not have to approximate the geometry using internal subsections. This avoids one of the above mentioned problems with the internal triangles.
Also importantly, the Finite Element mesh will define the geometry very accurately: the true shapes can now be given to the meshing algorithms, resulting in an accurately geometric description of the Finite element locations, including arcs.

Noticeable changes

The new PLAXIS 3D geometry data model will show us smoother meshes with higher quality elements for curved shapes like piles, shafts and tunnels:

Figure 5. Cylinder shape and  fine mesh. Left in PLAXIS 3D 2013, right PLAXIS 3D 2016

As can be seen in the image above, the cylindrical shape will give us a smoother shape, more evenly distributed elements and a better geometrical description with less elements. Overall this will give us higher quality meshes with less elements. Since the calculation time is highly influenced by the number of elements, we will gain calculation speed improvements by having a better description of the Finite Element mesh geometry.

Shape designer

Arcs: no segments

Since PLAXIS 3D AE, the shape designer does not use segments anymore to define a curved shape: we now support parametric geometry for these arc-shapes, and so we do not need to approximate the curved shape anymore using small straight sections. So if you want to describe a circle, it can just be done without using segments, and the internal geometry description will make it a true circle (or cylinder).

Standard shapes

Some standard shapes can be generated using a command. This includes a cylinder, cone and cuboid. In older versions (3D 2013, and before) the commands for a cylinder and a cone still supported segments along the curved shape, but since 3D AE these shapes internally use a mathematical description.

Figure 6. From left to right: a cylinder, cone and cube

Command examples

cylinder
Signature: cylinder radius height (x_O y_O z_O) (x_V y_V z_V)
To create circular volume pile with its top center point at (5 5 0), a length of 8 m vertically downward (vector direction will be (0 0 -1)) and a diameter of 0.80 m (radius = 0.4 m) we can use this command:

cylinder0.48(220)(00-1)

cone
Signature: cone base_radius height (x_O y_O z_O)
To create a cone with a base radius of 1.2 m, a height of 4 m with its base centre point at (6 2 -5) we can use this command, pointing up (0 0 1):

cone1.24(62-5)(001)

cuboid
Signature: cuboid sidelength (x_O y_O z_O)
To create a cube with sides of 2.5 m, with the bottom side's centre located at the (10 0 -6), use this command:

cuboid2.5(100-6)

Pile geometry
The cone command can now also be used to create a tapered pile directly:

Figure 7. Tapered pile

See also the Command and objects reference and the compatibility notes for commands for more details.

Reading older PLAXIS 3D files

When reading older PLAXIS 3D files that contain (triangle based) tessellated geometry,  PLAXIS 3D 2016 will attempt to convert this tessellated geometry to the parametric geometric data structure.

• Boreholes: Soil layers defined via boreholes used to be stored as tessellated geometry in PLAXIS 3D AE, 3D 2013 and older. When loading a model in PLAXIS 3D 2016 (and newer), these boreholes and their resulting soil layer definition will be regenerated using parametric geometry.
• Surface and volumes: Surfaces and volumes created in PLAXIS 3D AE are already defined as parametric geometry, and so these can directly be loaded in PLAXIS 3D 2016. However, geometry created in older versions (3D 2013 and older) as well as geometry imported from CAD files are based on triangulated, tessellated definition, and cannot be directly loaded into PLAXIS 3D 2016. PLAXIS will attempt to load these triangulated shapes by converting all internal triangles into parametric definitions. When the geometry has a limited amount of triangles, this can be achieved. However, if the geometry consists of many triangles, this will not be possible, and these surfaces and volumes will not be loaded in PLAXIS 3D. Hence, these geometric objects are removed from the Plaxis model.

Whenever PLAXIS 3D detects it needs to change the geometry to make the transition from triangulated/tessellated geometry to fully parametric geometry, the new geometry will require a new intersection. Following from this, a new mesh will need to be generated and the project will need to be completely recalculated.
Hint: if you have selected points for curves, then make sure to reselect them again before the calculation via the Select points for curves option in Output or directly via the command line in Input.
The program will directly store the file under a new name to prevent accidentally overwriting the original file. The new PLAXIS 3D file will be stored in the same folder and "_converted" will be added to the filename.

In some cases, the required changes are too great, or critical triangulated shapes are removed from the model. In that case, it is recommended to use a hybrid version of PLAXIS 3D that supports both triangulated and parametric geometry. This hybrid version will be available as PLAXIS 3D Classic (similar to 3D AE but with some updates). PLAXIS 3D Classic will be located in a subfolder of the PLAXIS 3D installation folder called "classic". To start Input for PLAXIS 3D Classic, start Plaxis3DInput.exe from this subfolder "classic".

Import of CAD geometry files

Since PLAXIS 3D 2016 only allows parametric geometry, and does not accept triangulated geometry, the program can no longer import CAD files based on triangulated geometry. This means PLAXIS 3D will no longer support the import of *.3DS, *.DWG, and triangulated *.DXF.

For more details on the support import types, please see the page on How do I import a geometry in PLAXIS 3D?

If you still need to import these CAD files using triangulated geometries, PLAXIS 3D Classic is still available for this.

Conclusion

With the fully parametric geometry data in PLAXIS 3D 2016, we solved problems with intersection, mesh quality for curved shapes and interface locking. PLAXIS 3D 2016 will provide you with:

• Fewer problems during intersection;
• Fewer performance issues;
• Fewer issues in mesh generation;
• Improved mesh quality with fewer elements required;
• Faster calculations due to fewer elements when having curved shapes;
• More accurate results when using curved shapes, especially when loaded in shear.

This major change to PLAXIS 3D will make the program faster, more reliable, more accurate, and better equipped for geotechnical challenges, especially when dealing with large and complex geometries.