In Plaxis the gravity value is only relevant for full dynamic calculations. Input for non-dynamic calculations is the volumetric weight of soil and water in which the gravity is implicitly included.
However due to an issue the kernel always uses the default value of 9.8 (m/s2) during full dynamic calculations. Other gravity values resulting from changes to this default gravity value or when switching to non-metric units are not taken into account correctly. This will result in an incorrect calculated mass and thus in wrong results for full dynamic calculations in PLAXIS 3D 2012 and PLAXIS 3D 2013.00.
This issue has been solved in the PLAXIS 3D2013.01 version.