Multiscale evaluation of bio-treated residual granitic soil strength for sustainable applications

By the end of the 21st century, eliminating plastic waste and promoting sustainable reuse will remain critical challenges for sustainable infrastructure development and environmental management. This research delves into the mechanical, microstructural, and modelling characteristics of residual granitic soil (RGS), enhanced by the incorporation of polybutylene succinate (PBS) and xanthan gum (XG), subjecting the treated samples to steam curing at 16°C for 7, 14, and 28 days. In addition, the effect of Zn (at 175mg/kg) and Cu (at 144mg/kg) and the effects of CO₂ curing after the 28-day curing period have been examined. Also, the structural, morphological, surface, thermal, spectroscopic, and magnetic resonance analyses, i.e., XRD, SEM, MIP, BET analysis, TGA, FTIR, and NMR, respectively, are harnessed to assess the PBS-XG-treated RGS mixtures. The isolated effect of PBS and binary effect (PBS-XG) on the physicochemical properties (LL, l_s, G_s, and pH, respectively) are evaluated in detail. The research findings revealed that the composite soil mixed with 0.2% PBS and 1.5% XG (in ternary mixes) exhibited superior performance. The effects of Zn and Cu contamination and CO₂ sequestration and microstructure indicate that an optimal dosage level of PBS-XG promotes a stable and compact particle configuration in RGS. Finally, detailed gene expression programming (GEP) modelling was performed to derive simple-to-use mathematical expressions. The GEP model was formulated to determine that UCS_28-day possessed superior performance (R²_TrD =0.773, R²_TsD =0.750). Hence, the sustainable treatment of residual granitic soils not only enhances soil strength but also contributes to environmentally responsible ground improvement practices, offering valuable implications for research and applications in engineering geology.