A BOUNDING SURFACE FOR GRANULAR MATERIALS

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A laboratory investigation has been carried out into initial anisotropy and into the effects of continuous principal stress rotation on the undrained behaviour of two granular materials : a natural angular to sub-angular sand and glass ballotini, which comprises spherical grains. Pluviated samples of loose Ham river sand and of ballotini, having the same grading, were isotropically consolidated, then subject to undrained shear in a hollow cylinder apparatus, using a constant b(=(σ_2-σ_3)/(σ_1-σ_3))=0.5. Despite the marked contrast in their grain shapes, both materials displayed stress-strain, strength and pore pressure responses which were strongly dependent on α, the direction of the major principal stress to the vertical during shear.For both materials a surface may be defined in q((σ_1-σ_3)/2)-P'((σ_1'+σ_2'+σ_3')/3)-α space which portrays their undrained initial anisotropy. The surface is shown to be a bounding surface in that it separates possible from impossible states.The bounding surface is capable of anticipating the response of the materials to stress paths involving principal stress rotation, both monotonically and cyclically applied. It distinguishes different patterns of behaviour on the basis of the direction in which principal stresses are rotated and whether effective stress paths travel on or below the surface.The bounding surface is restricted to the stage of undrained shear during which positive pore pressures are generated and levels of octahedral shear strain are, by observation, less than 0.5%.
社団法人地盤工学会の論文
1987-12-15

A BOUNDING SURFACE FOR GRANULAR MATERIALS

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