Large-displacement interface shear between steel and granular media

A systematic study is reported of the behaviour of graded silica sands and a silica rock flour silt, sheared against steel interfaces. Ring shear experiments investigated the influences of interface position, displacement scale, normal stress level and particle size distribution on ultimate interface friction angle, delta(cv)'. Grain crushing is shown to play an important role within a concentrated shear zone, and this process, along with changes in the roughness of the interface, could lead to delta' values markedly different from those developed in conventional small-displacement direct shear tests. It is also shown that delta' measurements at smaller displacements may depend on whether the interface is mounted above or below the sample, but that such differences diminish to zero when displacements are large. The finding that delta' is strongly displacement-dependent over the single-millimetre to multiple-metre scale has many practical geotechnical engineering implications.