Hydraulic conductivity of tyre-derived aggregate for leachate collection and removal

Abstract

This paper presents the determination of horizontal and vertical hydraulic conductivity in large-particle-sized tyre-derived aggregate (TDA) – that is, TDA with particle sizes over 50 mm – as a substitute for gravel in landfill leachate collection and removal layers. The determination of hydraulic conductivity was completed under applied surface stresses from 56 to 375 kPa, relating to 5–40 m of waste over a TDA drainage layer in waste disposal facilities. Hydraulic conductivity was determined indirectly from measurements of air permeability. At the final applied stress, hydraulic conductivity was measured directly to compare with the values determined from the air permeability measurements. The Forchheimer addition to the typical Darcy’s equation of flow was used to account for the effects of inertia from non-Darcian flows (as indicated from the Reynolds numbers). At all the applied stresses, after correcting for inertia, the equivalent horizontal and vertical hydraulic conductivity values for all TDA types tested were greater than 0.0001 m/s – a typical requirement for landfill drainage layers. The anisotropy in the hydraulic conductivity decreased with the applied stress from as high as 10 at 56 kPa to up to 2 at 375 kPa.