A new hollow cylinder torsional shear apparatus is described. The apparatus is suitable for investigating soil behaviour under generalized stress paths, including principal stress rotations, characteristic of earthquake and offshore-wave loadings. A new, more rational assessment of stress nonuniformity across the wall of the hollow cylinder specimen is made, and the "no go" regions of the stress space are delineated that limit stress nonuniformity to acceptable levels. Operation of the apparatus and experimental procedures for tests on reconstituted specimens of sand are described. Typical results of drained tests on loose and dense sand are presented to illustrate the capabilities of the apparatus as a general stress-path loading device and to highlight the stress-path dependence of soil behaviour, in particular, the deformation response to principal stress rotations. Key words: hollow cylinder apparatus, generalized stress paths, principal stress rotation, sand, deformations.

Review and assessment of sand sample preparation techniques from both theoretical and experimental viewpoints are presented. Sample densities obtained by air pluviation are shown to be sensitive to rate of pouring and drop height. Terminal velocity is reached at a very small drop height, and homogeneous samples of the same initial density tend to be formed by pluviation of uniform sand in water. Uniformly dense samples obtained by vibration of loose pluviated samples show no detectable difference in behavior when compared to samples densified by control of drop height only. Effective confinement during densification by vibration appears to prevent formation of a loose top layer. A loose top layer in an otherwise dense sample leads to a marked decrease in liquefaction resistance. Preparation of triaxial sand samples by pluviation in water is recommended because it results in initially saturated specimens, and homogeneous samples of desired densities can be replicated without difficulty.

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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.

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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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