News

May 20, 2009

Plaxis 3D Foundation version 2.2 – known issues

In the latest Plaxis 3D Foundation released version, some issues have been found.

Borehole water settings in calculation phases

In Plaxis 3D Foundation it is possible to define a water level in the boreholes to define a general phreatic level. During phases, users are allowed to change the water level in the boreholes, or to control the water pressures by changing the water pressure distribution per cluster.
When the water level is changed in a borehole, it will affect the general phreatic surface of the complete model for that phase. For Plaxis 3D Foundation Version 2.2 it has been found that when opening an existing project, borehole water levels that are changed in calculation phases are lost and reset to those used in the geometry/drawing mode.
This only effects the borehole water settings per phase after opening an existing project, not the settings per cluster.
For now, users are advised to check the pore pressure distribution, and their borehole water settings especially, prior to a calculation. The easiest way is to open the preview for a phase and check if the displayed pore pressures are correct.

Custom borehole water settings

Plaxis 3D Foundation allows for a user defined pore pressure distribution per layer in the borehole by specifying a WPress+ and WPress- per layer boundary for a non-hydrostatic case. The actual pore pressure calculation gives wrong results when a work plane is located between two soil layer boundaries: this results in large tensile pore pressure values in the groundwater pressure calculation. In order to check if the pore pressures are generated correctly, please open the preview of the desired phase and check the pore pressure distribution by viewing the shadings, or define a cross section and see the stress distribution plane.
When these pore pressures are not generated correctly, users are advised to use the cluster defined pore pressures to generate the correct pore pressures. These are also stored correctly (see the issue above).

For both these issues with the water settings in the boreholes, Plaxis is investigating the issues how to solve these.

Soft Soil Creep's K₀^NC

In Plaxis 3D Foundation, it looks like users are allowed to change the value of K₀^NC for a Soft Soil Creep soil material. However, this is not possible: it will always be changed back to the default value based on the dilatancy angle.

Use of embedded piles with Soft Soil Creep / User Defined Soil Model
The 3D Foundation Version 2.2 calculation kernel cannot handle the combination of an embedded pile with certain soil models:

• embedded pile + Soft Soil Creep: in order to determine the behaviour within the embedded pile's elastic zone, the stiffness is determined from the global stiffness. This leads to a wrong determination of the pre-consolidation stress (p_p), that can result in e.g. a NaN error that stops the calculation.
• embedded pile + User Defined Soil Model: for a user defined soil model it is not always evident in what state variable the current stiffness parameters are stored. This current stiffness is needed to calculate the behaviour in the elastic zone around an embedded pile.

Both resulted in phases that could not be calculated.

Plaxis is currently resolving these issues with the combination of embedded piles and the Soft Soil Creep model or the User Defined Soil Model. This fixed calculation kernel will be available upon request. If you encounter this problem, please contact the support department to receive download and installation instructions.

Loads on vertical planes under walls
When a distributed load on a vertical plane is placed directly below a wall element, the mesh generation is not able to generate the load vectors for this vertical plane just below the wall elements. This can be seen in the generated mesh: there are no loads shown on the vertical surface just below the wall elements.
Users are advised to define wall elements where there are missing distributed loads. In the staged construction mode, please do not activate these artificial walls. For the introduced interfaces, please use a soil material just as the surrounding soil, but with the interface strength reduction factor Rinter set to rigid.

Add anchor rows by the grid/group designer
For some modelling issues, people will define anchor rows on different vertical work planes. When these anchor rows are placed via a grid of points on the same (X,Z) coordinates in the horizontal work plane, it sometimes looks like the program does not respond and it will not add new anchors to the geometry.
In order to add these anchors, please use the select tool (the icon with the arrow in it), click on the surrounding cluster where to add the anchor, and then start adding new anchors again.