Permeability of mine tailings measured in triaxial cell

Abstract

The execution of permeability tests using a triaxial cell makes it possible to eliminate the uncertainties that characterize tests performed using conventional equipment. This paper contains the results of 48 tests carried out on three materials recovered from tailings of Riotinto mines (Spain). The equipment involved a modified triaxial system to facilitate the execution of permeability tests under constant head. The tests were performed on samples consolidated to 50, 100, 200, and 300 kPa for four different hydraulic gradients established by applying a backpressure difference (ΔBp). The magnitude of the backpressure difference was applied as a percentage of the initial effective consolidation pressure, expressed as ΔBp/σ′c; namely, values of 10%, 15%, 20%, and 25%, which resulted in hydraulic gradients between 5 and 80. The backpressure (Bp) was constant (400 kPa) in all cases, allowing a degree of saturation close to 100% to be achieved. This was verified by calculating Skempton’s B parameter, which was very close to unity in all cases. The results indicate that it is feasible to define an empirical function including the coefficient of permeability (k) and the effective consolidation pressure (σ′c), the mean effective confining pressure (σ′cav), and the backpressure differential (ΔBp).