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: i) drained and undrained triaxial compression tests; ii) 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); iii) drained and undrained triaxial extension tests; and iv) 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: i) the CSL in the compression plane does not depend on θ or on stress-path; ii) the stress-dilatancy is dependent on θ while the effect of θ on state-dilatancy is minor; iii) the undrained yield strength of LMT was found to not significantly depend on state parameter (ψ) but it was significantly affected by the stress-path followed during consolidation and subsequent shear, e.g. 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.