In PLAXIS 2D and PLAXIS 3D a pseudo-static acceleration can be defined per phase in the Model Conditions > PseudoStatic option in the Model explorer:

Figure 1. The PseudoStatic option in the Model explorer

By activating the PseudoStatic option in a phase, and specifying the acceleration value in at least one of the components, these pseudo-static accelerations will be activated in the calculation. The input values of the x- and y-acceleration (and z-acceleration) for 3D components are expressed in terms of the normal gravity acceleration g.

Model response

When e.g. a positive vertical pseudo-static acceleration is applied, the model responds analogue to objects in an elevator that accelerates in an upward motion. The objects inside the elevator tend to feel as if a vertical force in a downward direction is applied to them. This is the same behaviour that can be seen in a pseudo-static calculation: with a positive vertical pseudo-static acceleration, the free boundary of the model will show behaviour that this free boundary has displacements in a downward direction. This is the opposite direction of the specified pseudo-static acceleration.
For horizontally applied pseudo-static accelerations the model responds in a similar way.