Soybean-urease-induced CaCO₃ precipitation as a new geotechnique for improving expansive soil

In this study, soybean-urease-induced CaCO₃ precipitation (SICP) was proposed as a new geotechnique for improving expansive soil without precedent. SICP-reinforced expansive soil (SRES) specimens, as well as unreinforced expansive soil specimens as control samples were prepared following standard proctor tests at various moisture contents (20, 23, 26, 29, and 32%). Differential free swell tests, expansive potential tests, swelling pressure tests, shrinkage tests, compression tests, direct shear tests, unconfined compression tests, particle size analysis tests, and scanning electron microscope tests were carried out on the specimens. The results reveals that SICP reinforcement prompts distinct increases in compacted dry density, UCS, cohesion, and internal friction angle of expansive soil, while induces a remarkable reduction in DFS, swell potential, swelling pressure, and shrinkage of expansive soil. For instance, the compacted maximum dry density increases from 11.5 kN/m³ for UES to 12.5 kN/m³ for SRES and the optimum moisture content decreases correspondingly from 26.4% for UES to 23.6% for SRES. Furthermore, the reinforcing mechanics of SICP for expansive soil are analyzed and graphically presented. In conclusion, this research identifies SICP reinforcement to be an effective solution to problematic expansive soil and provides fundamental data for engineering practices.