Problem description

In the material set window we can specify in the tabsheet “Initial” an overconsolidation through either an Over Consolidation Ratio (OCR) or Pre Overburden Pressure (POP) value. These values will influence the generation of initial (horizontal) stresses by means of the K0-procedure.

However unexpected behaviour is that in the mentioned Plaxis versions the specified POP value will also influence the generation of initial (horizontal) stresses in a non-K0 phase (i.e. gravity loading, plastic and consolidation phase). The kernel will take the overconsolidation into account to determine the initial position of the hardening cap resulting in higher horizontal stresses than is expected based on the K0nc.

Notes:

• this behaviour is only relevant for material models that allow input of a POP value (i.e. advanced models such as HS and SS);
• this behaviour does not occur when using OCR values, since these values relate to the stress at the start of the phase (which is zero for newly activated clusters and as such does not result in a moved position of the hardening cap);

Solution

Work around for this situation is to create a copy of the original material set with the non-zero POP value and to set this value to zero. This material set should then be used/applied after the K0 phase.

This issue has been solved in PLAXIS 2D AE.