The circular economy encourages the production and consumption of sustainable embankment geomaterials and their blends utilizing recycled waste materials in roads, railway tracks, airfields, and underground structures. Geomaterials comprising high-plastic soft expansive clay pose excessive settlement during cyclic traffic/railway/airfield loading resulting in uneven geometry of overlying layers. This paper demonstrates multiobjective optimized improvement of expansive clay (C) geotechnical characteristics by cost-effective agro-wastes additives at microlevel (by 3% to 12% rice husk ash, i.e., RHA), nanolevel (by 0.6% to 1.5% rice husk derived green nano-SiO2, i.e., NS), and synergistic micro to nanolevel (NS-RHA). The swell potential, resilient modulus (MR), initial elastic modulus (Es), unconfined compressive strength (UCT), and California bearing ratio (CBR) of C and its blends were determined. The chemical characterization of C and its blends were conducted through Fourier transform infrared spectroscopy (FTIR) and optical microscopic tests. The outcome of this study depicted that the cost ratio for the optimized composite, i.e., (1.2% NS-9% RHA)/(9% RHA) is 1.22 whereas stiffness ratio MR (NS-RHA)/MR(RHA) and Es (NS-RHA)/Es(RHA) and strength ratio UCT(NS-RHA)/UCT(RHA) and CBR(NS-RHA)/CBR(RHA) were found to be 2.0, 1.64, 2.17, and 2.82, respectively. FTIR revealed the chemical compatibility between C, RHA, & NS from durability perspective. Cost-stiffness results of this study can be applied by geotechnical experts to economize the green stabilization of C by use of agro-waste for sustainable development.