Granular Solid Hydrodynamics (GSH): a broad-ranged macroscopic theory of   granular media
  A unified continuum-mechanical theory has been until now lacking for granular media, some believe it could not exist. Derived employing the hydrodynamic approach, GSH is such a theory, though as yet a qualitative one. The behavior being accounted for includes static stress distribution, elastic wave, elasto-plastic motion, the critical state and rapid dense flow. The equations and application to a few typical experiments are presented here. 
Yimin Jiang and Mario Liu
cond-mat.soft