Problem description

Just like the calculation type Consolidation with minimum excess pore pressures, the Consolidation analyses with the Degree of consolidation criterion should not allow any additional loading, i.e. “staged construction” changes: no change of loads, materials, water pressures, etc.

However, for the Degree of Consolidation option, it is possible to manually change the pore pressure calculation type in PLAXIS 3D 2013. When the definition of the pore pressures is manually adjusted AND this leads to a different steady state pore pressure distribution compared to its parent phase, it will cause an undesired (and maybe unexpected) change in the steady state pore pressure distribution in the consolidation phase.

This is only an issue when manually changing the pore pressure calculation type of either the Degree of consolidation phase, or its parent phase after the creation of both phases. Otherwise, any change in the parent phase’s phreatic levels, volume specific water conditions and/or boundary conditions will be correctly updated in the Degree of consolidation phase. To check this, see these items in the Model explorer and Selection explorer.

Please also see the related issue about the use pore pressures from previous phase.

Solution

This issue is now fixed in PLAXIS 3D AE.00: it is no longer possible to set the pore pressure calculation type for a Degree of consolidation calculation to something else then Use pressures from previous phase.

In 3D2012 and 3D2013.0 versions the pore pressure calculation type for the Degree of consolidation calculation type should be manually set to Use pressures from previous phase.

Advanced workaround for 3D2013

With the set of commands below, it is possible to do this in one go via the Expert > Commands Runner option for any configuration of phases:
groupfiltered Phases "ShouldCalculate=True"
groupfiltered groups[-1] "DeformCalcType=Consolidation"
groupfiltered groups[-1] "Deform.LoadingType=Degree of consolidation"
apply groups[-1] "setproperties" "PorePresCalctype" "Use pressures from previous phase"
__writephasestomesh groups[-1] True
ungroup groups[-1]
ungroup groups[-1]
ungroup groups[-1]

This list of commands will only change the phases that still have to be calculated, and includes a workaround for the related issue Use pressures from previous phase.