<p>High plasticity clays are prone to excessive deformation and low load-bearing capacity, which frequently leads to structural instability in geotechnical applications. To address these challenges, sustainable and cost-effective stabilization strategies such as the incorporation of nanomaterials and industrial by-products are receiving increasing attention. This study investigates the combined effects of ground granulated blast furnace slag (GGBFS) and nano-silica (NS) on the compressibility, consolidation, and swelling behavior of high plasticity clay using Atterberg limits, standard Proctor compaction, one-dimensional consolidation, and swell tests. Microstructural changes were also investigated using SEM, EDS, and XRD, providing insights into gel-like reaction products and the evolution of soil fabric. Experimental data indicate that the combined use of GGBFS and NS leads to enhanced consolidation-related stiffness (E_oed), faster consolidation, and reduced swelling in high plasticity clays. The observed improvements in compressibility, consolidation-related stiffness, and swelling behavior are attributed to microstructural refinement induced by stabilization. These effects are associated with pozzolanic reactions, micro-filling, and the formation of gel-like products, as supported by SEM, EDS, and XRD observations. This work demonstrates the integration of GGBFS and NS as a promising strategy for improving the compressibility and swell-related behavior of high plasticity clays.</p>