EVALUATION OF THE HYDRAULIC CONDUCTIVITY OF RICE HUSK ASH-TREATED LATERITIC SOIL–BENTONITE MIXTURES FOR WASTE CONTAINMENT

The safe containment of municipal solid waste depends on barrier materials that restrict the movement of leachate into soil and groundwater. This study evaluates the hydraulic conductivity and associated engineering behaviour of lateritic soil–bentonite mixtures modified with rice husk ash (RHA). Lateritic soil obtained from Shika–Zaria, Nigeria, was blended with 0, 5, 10, 20 and 30% bentonite and 0, 5, 10, 15 and 20% RHA. The mixtures were compacted using British Standard Light (BSL), British Standard Heavy (BSH) and West African Standard (WAS) efforts. Hydraulic conductivity was measured with a rigid-wall falling-head permeameter after saturation, while compaction, Atterberg limits and unconfined compressive strength were also evaluated. The natural laterite contained 67.58% material passing the BS No. 200 sieve, had a liquid limit of 33.60%, plastic limit of 15.39%, plasticity index of 18.21%, linear shrinkage of 12.86%, and was classified A-6 under AASHTO and CL under ASTM. Under BSH compaction, maximum dry density decreased generally as RHA content increased, whereas optimum moisture content increased. The highest recorded MDD for the investigated series was 19.42 kN/m³ for 5% bentonite–95% laterite without RHA, while the lowest reported value was approximately 13.73 kN/m³ at high bentonite/RHA treatment under the lower-energy conditions. The reported hydraulic-conductivity envelopes ranged from 5.648×10⁻⁸ to 32.01×10⁻⁸ m/s across the investigated mixtures and compaction conditions. The lowest measured value was 5.648×10⁻⁸ m/s, while the highest was 32.01×10⁻⁸ m/s. Compaction effort and moulding water content had pronounced effects on hydraulic conductivity. Overall, the results demonstrate that locally available lateritic soil and RHA can be incorporated into soil–bentonite barrier materials.