An investigation of shear mechanisms at interfaces between particles and re
latively smooth materials using contact mechanics and basic friction theory
reveals that a combination of sliding and plowing governs dense Ottawa 20/
30 sand/smooth high density polyethylene geomembrane peak interface shear b
ehavior. Contact area and the corresponding shear resistance during sliding
increase at a slower rate than the applied normal stress, resulting in a d
ecreasing friction coefficient and flattening of the peak strength envelope
. Plowing of soil grains results in an increasing peak friction coefficient
with increasing normal stress and can produce an upward curvature of the s
trength envelope above a critical stress level. Plowing is primarily contro
lled by the relative hardness of the interface materials and by grain shape
with angular particles exhibiting plowing in all normal stress ranges, whe
reas nearly perfect spheres exhibit only sliding. High surface hardness is
shown to constrain shear behavior to a sliding mode with little contributio
n from plowing. These findings sire consistent with results reported in the
tribology Literature.