Is it possible to deactivate the effect of water so that FLAC adds the amount of steady state PWP to the effective stresses in all zones such that all the stresses in the soil constitutive model are considered as the total stresses hereinafter?
Yes, it is possible to perform analysis in dry state conditions and saturated conditions in your numerical simulation. If you want to simulate the water table effect simultaneously then it can be done in stages wise analysis..in one stage water effect is considered and in other stage not considered. I suggest you to refer FLAC manual or research publication related to your topics based on FLAC for ready reference to your problem. all the best..
Do a mech ON but flow OFF analysis by setting the bulk modulus of water to zero which represents dry soil condition. Now if you step the model to equilibrium, the effect of previously existed PWP will get vanished and the total stress will be same as effective stress.