Fundamentals of constitutive equations for geomaterials

Constitutive equations for geomaterials constitute a very intricate field. In the first part of this chapter, a synthetic view of constitutive formalism is presented. An intrinsic classification of all existing constitutive relation is deduced. Then examples of incrementally non-linear relations are given and some applications follow. A numerical study of the so-called “yield surfaces” is presented, and is followed by a discussion on the validity of the principle of superposition for incremental loading. Finally the question of the existence of a flow rule is discussed for both axisymmetric and 3D conditions. In agreement with discrete element computations, it is shown that a flow rule can exist in 2D and not in 3D.