Effect of Grain Shape and Relative Humidity on the Nonlinear Elastic
Properties of Granular Media
Abstract
This study focuses on unraveling the microphysical origins of the
nonlinear elastic effects, which are pervasive in the Earth’s crust.
Here, we examine the influence of grain shape and relative humidity (RH)
on the elastic nonlinearity of granular assemblies made of spherical
glass beads and angular sand particles. We find that their elastic
nonlinearity is of the same order of magnitude. However, while the
elastic nonlinearity of glass beads increases with RH, that of sand
particles is rather RH independent. We attribute this difference to the
angularity of sand particles; absorbed water on the spherical grains
weakens the junctions making them more nonlinear, while no such effect
occurs in sand due to grain interlocking. Additionally, for one of the
nonlinear parameters that likely arises from shearing/partial slip of
the grain junctions, we observe a sharp amplitude threshold in sand
which is not observed in glass beads.