  It is recalled that stress-strain incremental modelling is a common feature
of most theoretical description of the mechanical behaviour of granular
material. An other commonly accepted characteristics of the mechanical
behaviour of granular material is the Rowe's relation which links the dilatancy
K to the ratio B of vertical to lateral stress during a test at constant
lateral stress, i.e. B=(1+M)(1+K). We combine these two features and extract an
incremental pseudo-Poisson coefficient which varies with the stress ratio . We
solve the oedometric-test case, starting from isotropic sample and stress, for
which the vertical stress is increased continuously. It is found that the
stress ratio B evolves towards an asymptotic value ko which depends on the
friction angle only. It is shown that this asymptotic value ko compares well
with the experimental fit known as the Jaky constant.
