Suction effects on the shear strength behaviour of compacted dewatered tailings

The paper presents the results from suction-controlled triaxial tests on compacted Dewatered Tailings (DT) carried out to evaluate their shear strength behaviour under rapid loading. Specimens were prepared via static compaction to a target dry density of 1.55 g/cm3 and water content of 18.5%. This produced an initial soil suction around 50 kPa. Compacted specimens were then subjected to a wide range of suction and loading paths prior to shearing. Specimens were finally sheared under ‘undrained’ conditions with suction monitored, not controlled, during the rapid loading. The triaxial results show that, in addition to the influence of confining stress, suction plays a key role on the shearing behaviour of compacted DT specimens. The higher the suction before shearing, the higher the material stiffness and peak deviatoric stress. Triaxial results are analysed using the Bishop’s effective stress concept, assuming that the coupling parameter χ is equal to the degree of saturation (χ=Sr). A unique Critical State Line (CSL) is obtained when adopting this simple approach, which permits the direct comparison of unsaturated and saturated tests results. Finally, the paper discusses the practical implications of the experimental results on the stability of DT deposits.