Hydraulic Conductivity of Compacted Lateritic Soil Partially Replaced with Metakaolin

Abstract

The study investigates the potentials of using metakaolin (MK) to improve the properties of compacted lateritic soil for hydraulic barrier system for containment of municipal solid waste (MSW). Oxide compositions determined by the X-ray fluorescence (XRF) show that MK contains Silicon oxide, SiO₂ (53.4 %), Aluminium oxide Al₂O₃ (34.2 %), Titanium oxide, TiO₂ (5.97 %) and Iron oxide, Fe₂O₃ (3.84 %) in high proportion. The soil was replaced with 0 %, 5 %, 10 %, 15 % and 20 % MK and compacted using four compaction energy levels namely: the Reduced British Standard Light (RBSL), British Standard Light (BSL), West African Standard (WAS) or “Intermediate” and British Standard Heavy (BSH) over a range of molding water contents (10 - 25 %). Unconfined compressive strength (UCS) and hydraulic conductivity tests were conducted and the results obtained were used to evaluate whether the lateritic soil partially replaced with MK conforms with the specifications for barrier systems for MSW containment. The results of this study show a general improvement in UCS of the soil specimens with increase in the percentage replacement of MK. Results of the study also show that hydraulic conductivity values of the specimens permeated with leachate are better than the results of hydraulic conductivities obtained when de-ionized water (DIW) was used as the permeant fluid. The specimens replaced with 5-20 % MK and compacted using the BSH compaction energy yielded hydraulic conductivities on the orders of 6.3 x 10^-10 m/s to 2.2 x 10^-10 m/s when DIW was used as the permeant fluid. On the other hand, the specimens compacted using the WAS and BSH compaction energies and permeated with leachate yielded hydraulic conductivity values in ranging from 6.8 x 10^-10 m/s to 3.6 x 10^-11 m/s. These hydraulic conductivity values met the regulatory maximum hydraulic conductivity (i.e. ? 1 x 10^-9 m/s) for construction of liner and cover systems for MSW containment.

Keywords: Compaction energy, Metakaolin, Hydraulic conductivity, Unconfined compressive strength, Municipal solid waste leachate, De-ionized water