UNDRAINED SHEAR STRENGTH BEHAVIOUR OF SAND-PALM KERNEL SHELL MIXTURES FOR BACKFILL APPLICATIONS

Sand is a key material in civil engineering, particularly as a backfill for road foundation construction. Using unsuitable materials or poor construction methods in this layer can cause premature pavement failures such as rutting, cracking and potholes, reducing road lifespan, increasing maintenance costs and compromising safety. With global sand depletion posing environmental and economic challenges, alternative materials are needed to sustain infrastructure projects. One potential substitute is palm kernel shell (PKS), an agricultural by-product generated in large quantities by the palm oil industry. This study examined PKS particles (<2 mm) mixed with sand of similar size to evaluate their effects on undrained shear strength. Samples were prepared with PKS substitution ratios of 0%, 25%, 50%, 75% and 100% (by dry mass of sand) and tested using the standard direct shear test (60 mm × 60 mm) in accordance with BS 1377:1990. The results showed that PKS significantly influenced the shear behaviour of the mixtures. The 75S:25PKS specimen achieved a shear stress of 18.40 kPa, which was comparable to 100S (17.48 kPa), although the 100PKS specimen achieving the highest peak shear stress of 30.31 kPa. It also showed approximately 51% greater vertical displacement, showing better deformability and less sand consumption. Overall, partial replacement of sand with PKS improves shear strength performance and presents a sustainable and cost-effective alternative material for road foundation backfills. The findings highlight the potential of PKS to enhance geotechnical performance while promoting waste valorisation and environmental sustainability.