Assessing the Impact of Rice Husk Ash on Soil Strength in Subgrade Layers: A Novel Approach to Sustainable Ground Engineering

The disposal of rice husk ash (RHA) in rice-producing regions poses critical environmental and public health challenges. However, RHA’s high amorphous silica content offers significant potential for soil stabilization, particularly in improving the mechanical properties of weak soils. This study investigates the shear strength of clay soil stabilized with rice husk ash (2%, 4%, 6%) and low cement dosages (2%, 4%, 6%) that incorporate layered subgrade systems (top, bottom, and dual-layer configurations). By optimizing rice husk ash incorporation with reduced cement content, this approach challenges conventional stabilization methods that rely heavily on cement. Sixteen soil-cement-RHA mixtures were evaluated through mechanical testing, supplemented by microstructural and elemental analyses using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Results demonstrated substantial improvements in shear strength across all subgrade layers. The dual-layer system with 2% RHA 6% cement (2%RHA6%C) achieved the highest cohesive strength (115 kN/m2) and maximum deviatoric stress (446 kN/m2). These findings highlight the viability of RHA as a sustainable, low-cement soil stabilizer, offering dual benefits: effective waste valorization and enhanced geotechnical performance. This study advances sustainable ground engineering practices by introducing a resource-efficient novel building material and provides a framework for layered stabilization systems in clay soils. Future investigations will focus on a broader range of soil types and extend the application of this approach to other sustainable ground engineering practices.