Valorization of Industrial Wastes as Alternative Liner Materials: Compressibility and Shear Strength

The increasing demand for sustainable waste containment systems has intensified interest in replacing conventional clay liners with alternative geomaterials derived from industrial by-products. This study addresses this gap by investigating the hydro-mechanical behavior of soil mixtures incorporating water treatment sludge (WTS), vegetal biomass ash (VBA), granitic mining waste (GMW), and blast furnace slag (BFS), with emphasis on their potential applicability as liner materials. A comprehensive experimental program was conducted, including one-dimensional oedometric consolidation, expansibility and swelling assessment, and consolidated undrained (CU) triaxial testing for mixtures containing up to 20% WTS and VBA, and up to 50% GMW and BFS, by dry mass. Optimized mixtures which achieved hydraulic conductivity lower than 10 -9 m/s were WTS15% with compression index of 0.129, cohesion of 25 kPa and internal friction angle of 31º, VBA10% with 0.090, 10kPa and 29º, GMW50% with 0.118, 0kPa and 35º, and BFS25% with 0.066, 0kPa and 35º, respectively. Additionally, those mixtures comprised swelling pressure lower than 25kPa and free swell lower than 15%. The results reveal two contrasting behavioral trends. Mixtures containing ash, mining waste, and slag exhibit reduced compressibility, lower swelling potential, increased shear strength, associated with improved particle packing and, in the case of slag, latent hydraulic reactivity. In contrast, sludge-amended soils display similar swelling and consolidation properties with reduced shear strength, due to their fine-grained, hydrated, and contractive structure, which promotes excess pore pressure generation under undrained loading, although decreasing swelling and consolidation parameters. Overall, the findings demonstrate that waste-based residues act as effective mechanical stabilizers, confirming that properly designed soil–waste mixtures can achieve a balance between environmental compatibility and mechanical stability, supporting their use in sustainable liner systems. These results contribute to the development of performance-based design criteria for waste-derived geomaterials in long-term containment applications.