Assessing Induced Pore Pressure and Suction Stress under Undrained Compression of Filtered Tailings

The stability of filtered tailings stacks requires a dense particle structure to be created via compaction following placement or potentially from desiccation due to atmospheric drying and/or compression due to self-weight. The generation of positive excess pore-water pressure in saturated or unsaturated filtered tailings can prevent sufficiently dense placement and affect the achievement of desired geotechnical performance. Undrained compression tests were performed on filtered tailings from two precious metal mines using a modified large-strain rigid-wall permeameter with controlled vertical stress. Specimens with different initial dry densities and gravimetric water contents were prepared to assess the impact of the initial placement conditions on the generation of positive excess pore-water pressure. In addition, a method is proposed and was investigated to estimate the effective stress of filtered tailings under undrained loading. The results of the study illustrated that unsaturated filtered tailings, when loaded incrementally, generated appreciable excess pore pressure near a degree of saturation of 80% when the dry density was at least 1.57 g/cm3. The excess pore pressure is considered to be appreciable when the ratio of positive excess pore pressure to the applied vertical stress is greater than 0.1. The generated pore pressure did not fully dissipate after 24 h. Results from this study demonstrate the interplay between placement water content and density, and illustrate that an equivalently dense structure may be achieved by both initial compaction or self-weight compression.