A preliminary numerical investigation of the micromechanics of snow compaction

Abstract

A dynamic finite-element computer program was used to examine the evolution of microstructure and its effect on continuum-scale deformation for the constant-speed uniaxial-strain compaction of an aggregate of roughly spherical elastic-plastic particles. Simulation results are used to explain some micromechanical aspects of snow compaction. Different compaction rates were used to examine the limits of quasi-static response and the effects of inertial stresses. Four stages of microstructurally controlled compaction were observed for quasi-static loading: particle re-arrangement, elastic deformation and two stages of plastic deformation. Elastic deformation follows the first critical density caused by the stable random loose-particle packing of rough spheres. Stage III compaction occurs by plastic deformation once stresses acting on particles exceed yield. Stage IV compaction follows a second critical density caused by the stable packing of deformed particles and is also through plastic deformation of particles. During high-speed compaction, inertial stresses propagate particle deformation from the loading platen into the aggregate. As a consequence, particle re-arrangement is limited so that the pressure-density ratio is larger for high-speed compaction than for quasi-static compaction at the same density. Hence, critical densities and the compaction-rate dependence of the pressure-density ratio during compaction of an aggregate of particles composed of rate-independent material are determined by the evolution of microstructure at different compaction rates. Observed pressure-density profiles for polar snow exhibit the same features of critical density and changes in the pressure-density ratio as found in the simulation and consist of four compaction stages: particle re-arrangement and three stages of creep particle deformation each following a critical density. Shear stresses appear to enhance the compaction during the stage III creep deformation of snow.