The postulate that the constant-volume friction angle [Formula: see text] of a granular material is unique and a function of mineral composition is verified experimentally. Granular materials comprised of particles ranging from minerals to metals are tested in a ring shear apparatus. Test samples are subjected to large shear displacements until a constant lower bound friction angle [Formula: see text] is mobilized. Possible effects of confining pressure, initial packing density, gradation, and particle shape on the value of [Formula: see text] are investigated. Friction angles mobilized in drained shear at the instant of maximum contraction and in undrained shear at phase transformation and steady state are compared with [Formula: see text] values. The experimental results confirm a broader fundamental significance of [Formula: see text] as a material parameter in that it is a consistent minimum drained friction angle equal to friction angles mobilized at phase transformation and steady state in undrained shear. Key words: granular materials, sand, friction angles, constant volume, steady state, phase transformation state, ring shear test.
Interface friction between an HDPE geomembrane and an angular as well as a rounded sand, a gravel, and a geotextile was investigated in a ring shear apparatus. The results indicate development of peak resistance at small strain and constant residual interface friction angles at large strain. The magnitude and difference between peak and residual friction angles increase with angularity. Interface friction angles between a geotextile and geomembrane were very low with no distinction between peak and residual. At composite interfaces, sliding occurred much more readily at a finer grained than a coarsegrained geomembrane interface. Key words: geomembranes, geotextiles, interface friction, granular materials.
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