Initial void ratio
Because the void ratio is one of the output parameters, it is necessary to specify its initial value 
. In general, the void ratio is associated with a certain state of stress and strain. Providing the initial void ratio 
is specified, it is assumed that its value corresponds to the state at the end of the first calculation stage (geostatic stress), see the theoretical manual.
In general, the evolution of void ratio 
has no impact on the evolution of strains and stresses. In such a case, the initial value 
influences only the plotted value of the resulting void ration. If this value plays no role in the analysis or is of no interest from the user point of view, its real value is irrelevant and one may adopt, as a point of departure, the one provided by the default setting, i.e., ein = 1.
The inputted value of the initial void ratio influences the stress-strain analysis in the following cases only:
- Material models which address dilation with the help of dilatancy angle ψ while considering dilatancy cut off once the current void ratio exceeds its maximum value
. Further details can be found for example in the description of the Drucker-Prager model. - When adopting the Hypoplastic clay model the current void ratio is a state parameter representing the degree of soil compaction, in which case it influences the stress-strain relationship. Therefore, providing a realistic value of the initial void ratio is in this case essential.
The initial void ratio appears also in the formulation of constitutive relations or when considering the dilatancy cut off in the Soft soil model or when adopting the critical state models, i.e., the Modified Cam-clay and the Generalized Cam-clay models. Therein, however, the initial void ratio is not an input parameter. Instead, it is determined automatically on the basis of the stress state at the end of the first calculation stage and parameters OCR or POP specifying the degree of preconsolidation.