Direct Shear Testing of Rockfill Material

Abstract

The shear strength of granular materials is mainly derived from the particle sliding friction and resistance resulting from reorientation and sample dilatancy. Parameters affecting the shear strength therefore depend on the relative density, gradation, particle strength, particle size and shape, and degree of saturation of the specimen. In this study a customized shear box is fabricated and used to perform direct shear tests of large diameter gravels. The effects of particle size, gradation, shearing rate and moisture on shear strength are investigated. Sample dilatancy is observed during shearing for all specimens. The internal friction angle increases with the increase of particle size and shearing rate; shear strength peaks with a sand and gravel mixture weight ratio of 0.6; the existence of moisture reduces the shear strength. The 6.3mm sample is sheared under a wide normal pressure range from 2kPa to 600kPa indicating a progressive flattening failure envelope.