During an undrained excavation/unloading (positive) tensile excess pore pressures (pexcess) may develop. Depending on the steady state pore pressures (psteady) the resulting total pore pressures pactive (which is the summation of the psteady and the pexcess) may also become positive in a certain area. Using a cavitation cut off value it is possible to limit these positive total pore pressures (pactive) to a certain value.
However, when the cavitation cut off is activated in the Calculations window the resulting excess pore pressures (pexcess) are actually cut off at the specified cavitation cut off value by the calculation kernel. This behaviour is wrong since the excess pore pressures should be cut off such that the total active pore pressure is limited to the cavitation cut off. As a result the calculated pore water pressures, effective and total stresses may not be correct.
This issue is partly fixed in the 2D2012.00 version. However note the related Known issue