This is a special record to model the volumetric stress part of a nonlinear material, given the experimental results of a volumetric compression test (compression in one direction, fixed size in other two directions).
The table specifies the strain-stress results for the volumetric compression test. Together with the poisson ratio as specified in group_materi_elasti_volumetric_poisson, an isotropic law in a nonlinear Young's modulus and a constant poisson ratio is fitted to this experiment. The Young modulues in fact is taken as the polynomial expansion where denotes the order of the polynomial expansion (as given in group_materi_elasti_volumetric_young_order).
The poisson ratio should be taken very high, say 0.4999999 or so, to ensure that the resulting law only models volumetric stresses. Then afterwards a normal young-poisson isotropic law (group_materi_elasti_young and group_materi_elasti_poisson) can be added to get an extra deviatoric part.