With the finite differences program by FLAC it is possible to dimension excavations in the alpine salt-rock in respect of the creep behavior. For this purpose creep parameters have to be obtained by long time laboratory tests on salt-rock samples with the help of FLAC. The parameter are evaluated by the labratory tests itself and by simulations of convergences of existing excavations in different levels. The advantages and disadvantages of the different creep laws in particular the in the finite differences program FLAC implemented creep laws classical viscolelastic (maxwell), two-components power law, the creep formulation by wipp and a viscoplastic model are discussed and the possible use in the dimension of mining excavations in rock-salt investigated.