Sekiguchi-Ohto viscid_Input parameter

I have a question on how to determine the coefficient of secondary compression and the intital volumetric strain rate as part of the input parameters of the Sekiguchi-Ohta viscid model. The Material Models Manual of Plaxis 2D suggests using a secondary compression index as an alternative to the above mentioned input parameters without any further informations on how to specifiy it. Unfortunately I haven't found a lot in the literature about this subject. The second question is wether it is possible or not to derive the input parameters of the Sekugichi-Ohro viscid model out of the input data set of the soft soil creep model using the soil test tool by excuting back calculations?