During liquefaction simulation with FLAC, it is necessary to specify porosity and permeability if the model considers pore pressure buildup and flowing of the fluid. The problem would be modeled with an impaired hydraulic response if realistic permeability values are not incorporated.

When working with PM4Sand, specifying porosity directly may not be important unless fluid interaction is simultaneously considered; however, permeability remains vital if generation and dissipation of pore pressure are to be modeled. On top of that, PM4Sand parameters must be duly initialized before any dynamic condition is set in.

In many FLAC examples, a first "solve" run is initiated after the assignment of model parameters, much like initializing the Finn model before commencing a liquefaction analysis. This allows the model to become equilibrated with respect to stress conditions prior to the application of dynamic loading. With that in mind, executing "solve" after the assignment of PM4Sand parameters will ensure a stable basis upon which liquefaction analyses can proceed with greater accuracy.

Thank you for your explanation Md Maruf Alam. May I ask another question?, it's still in same topic about dynamic simulation

It depends on your model type:

Hydro-mechanical model? → Yes, you must define them.

Dry mechanical model? → No, it’s not necessary.