Drained and undrained behaviour of a sandy silt gold tailings under general multiaxial conditions

A laboratory study was carried out on a sandy silt gold tailings to investigate the effect of the Lode angle (θ) on the critical state line (CSL) in the compression (e–p′) and effective stress (q–p′) planes, and to study the strength anisotropy of the tailings. Four sets of strain-controlled tests were carried out: (a) drained and undrained triaxial compression tests; (b) torsional shear hollow cylinder tests under drained and undrained conditions at constant θ and constant direction of the major principal stress relative to the vertical axis (α); (c) drained and undrained triaxial extension tests; and (d) undrained hollow cylinder simple shear tests. The tests were carried out on loose moist tamped (LMT) and dense slurry air-dried (AD) prepared specimens. The results indicated that: (a) the CSL in the compression plane does not depend on θ or on the stress path; (b) the stress-dilatancy is dependent on θ while the effect of θ on state-dilatancy is minor; (c) the undrained yield strength of LMT was found not to depend significantly on the state parameter (ψ), but it was significantly affected by the stress path followed during consolidation and subsequent shear, for example, by the pre-shearing stress ratio, stress-reversal loading, θ and α. The results demonstrate the contribution of the initial shear stress and evolving anisotropy on the undrained strength of the gold tailings in a loose state.