Problem description

In the indicated Plaxis versions some issues exists with the calculation of the maximum value used for the bulk modulus of water. This issue is only relevant for Undrained (A or B), Consolidation and/or Transient flow calculations

The following is happening: with an Undrained (A or B), consolidation or transient flow analysis the program calculates a bulk modulus for the water (K_w) based on the Input value of the effective soil stiffness (K’). The program by default uses a large ratio between K_w and K’ such that the Plaxis calculation obtains realistic behaviour, but not such that the Plaxis calculation has numerical problems.

Due to an incorrect rounding of conversion values from non SI-units to SI-units, the K_w value in the calculation did not have the correct value prior to PLAXIS 3D 2013.01. When this conversion value is rounded to zero, then the program will assume K_w to be equal to K_w,max, which will give a too high value for K_w.

This issue with unit conversion can have these effects:

• In case the value for K_w is too low, this issue will cause too low excess pore pressure to be generated, a too slow consolidation process or result in incorrect discharges in a transient flow calculation.
• When the value for  K_w is too high, the issue will cause too high excess pore pressures to be generated, a too fast consolidation process or results in incorrect discharges in a transient flow calculation.

Solution

This issue has been resolved in PLAXIS 3D 2013.01