soil property in ABAQUS?

Hi,
I am trying to simulate soil material (stiff clay & dense sand) in ABAQUS. I
searched online and got some parameters, such as density, young's modulus,
and poisson's ratio. I know attenuation is a major property for soil
material. However I was not sure whether I should use Rayleigh damping or
viscoelastic property. Anyone has experiences of simulating soil material in
ABAQUS? I would really appreciate if you could tell me where to obtain or
how to calculate those attenuation parameters. Thanks a lot!

Jerry


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