Viscoelastic material: Prony series in Abaqus

[yparkhi]

Hello Everybody,
I’m using Prony series to model viscoelasticity of an asphalt material in a pavement. I have defined the material properties through time-domain Prony series in Abaqus. The parameters are:
g_i (shear relaxation modulus ratio): 0.8
k_i (bulk relaxation modulus ratio): 0
tau_i (relaxation time): 1

I’m trying to understand what that series does. I have fiddled with these parameters and nothing seems to make any difference in the results. Can anybody please tell me what the significance of each term is? And how the system response affects by variation of these parameters?
Somebody please give me a push in the right direction here.

Thanks in advance.

Sincerely,
Yogesh