Have you ever gone through the ensuing procedure in your project?

[FLAC3D-5.0]:

Prior to running a dynamic model with actual material strength and damping properties, an elastic simulation should be made without damping, to estimate the maximum levels of cyclic strain and frequency response ranges of the model system. If the cyclic strains are large enough to cause excessive reductions in shear modulus, then the use of additional damping is questionable. In such a case, the damping will be performing outside of its intended range of application. The model properties and input amplitude should be checked if excessive strains are calculated throughout the model.