  In general, the evolution of soil submitted to simple stress-strain paths is
characterized using the 3d phase space (v,p',q) i.e. (specific volume, mean
intergranular pressure, deviatoric stress); one finds that all trajectories end
up at a line of attracting point called the critical-state line. The surface of
Roscoe (Hvorslev) is defined as the surface made of the last part of the set of
trajectories ending to a given critical point and coming from all states of
normally consolidated soils (from all states of over consolidated soils). It is
demonstrated that these two sets are part of the same surface, which is
confirmed by experimental data.
