Behaviour of loose sand under simultaneous increase in stress ratio and principal stress rotation

The drained behaviour of loose sands under simultaneous increase in stress ratio and principal stress rotation is investigated. The hollow cylinder torsional device, which permits independent control of four stress parameters, namely effective mean normal stress [Formula: see text], stress ratio R, intermediate principal stress parameter b, and the inclination ασ of the major principal effective stress [Formula: see text] to the vertical, is adopted as the testing device. Drained tests carried out on saturated sand indicate that deformations under increasing R and ασ are path independent, if the final stress state is within the approximate bounds of R < 2 and ασ < 45°. With increasing stress ratio R and (or) principal stress rotation, deformations gradually become path dependent. Once loaded to a stress state within the domain R < 2 and ασ < 45°, the strain response under subsequent principal stress rotation is shown to be independent of the previous loading history. It is demonstrated that the strain response under any general increasing R − ασ path in the domain of R < 2 and ασ < 45° can be predicted using the results of a limited number of tests characterizing that domain. Strain increment direction αΔε is shown to be approximately coincident with and totally governed by the stress increment direction αΔσ, when the stress increment direction αΔσ is preferentially inclined towards the vertical deposition direction. Key words : sand behaviour, hollow cylinder torsional device, principal stress rotation, stress-path testing.