Stability Evaluation of Landfill Liners Using Compacted Waste Foundry Sand and Bentonite

The construction of secure landfill liners consumes vast quantities of high-quality natural clay, leading to resource depletion and environmental concerns. Concurrently, the foundry industry generates significant amounts of Waste Foundry Sand (WFS), a by-product that poses disposal challenges. This study investigates the feasibility of utilizing WFS stabilized with bentonite as a sustainable material for landfill liner applications. WFS was mixed with bentonite (0% to 10% by weight) and compacted using British Standard Heavy (BSH) energy. Index properties, compaction characteristics, and Unconfined Compressive Strength (UCS) at 7, 14, and 28-day curing periods were evaluated. Results indicate that the addition of bentonite transformed the non-plastic WFS into a plastic material at 8% bentonite content and above. The Maximum Dry Density (MDD) decreased from 1.96 Mg/m3 to 1.6 Mg/m3, while the Optimum Moisture Content (OMC) increased from 17% to 21% as bentonite content increased from 0% to 10%. The UCS increased with both bentonite content and curing period, peaking at 383.61 kN/m2 for the 8% bentonite mixture after 28 days of curing. This value significantly surpasses the common regulatory benchmark of 200 kN/m2 for liner stability. The study concludes that an optimum mix of 92% WFS and 8% bentonite, compacted at BSH energy, provides a technically viable, sustainable, and economically beneficial alternative to conventional clay liners, effectively valorizing industrial waste while meeting critical geotechnical requirements for waste containment.