Sand as a compressible fluid

The macroscopic volume changes of granular bodies during compression and shearing are investigated in terms of compressible fluid. The proposed analogy between sand body and van der Waals fluid, and appropriate form of van der Waals state equation, is demonstrated interpreting common soil mechanics tests in which the deviator stress is proportional to the mean pressure. The equation fits well the large range of applied pressures, and the proposed regular behavior is observed despite the severe grain crushing during loading. The common position of sands in reduced coordinates is found. The simple expression for pressure in sand in isothermal conditions is also proposed.