In-situ bio-nano-silica formation in FICP-treated sand: from concept to application

Fungal-induced calcium carbonate precipitation (FICP) is a bio-mediated process that promotes calcium carbonate formation to strengthen sandy soils. However, its practical application in geotechnical engineering is limited by insufficient strength gains, revealing a critical research gap in achieving robust soil stabilisation. This preliminary study addresses this gap by introducing a novel hybrid treatment technique that combines FICP with bio-synthesis of nano-silica (Bio-NS) for in situ sand treatment. Scanning electron microscopy, energy-dispersive spectroscopy, and Fourier-transform infrared spectroscopy were used to characterise the microstructure of the treated sand. Unconfined compressive strength (UCS) tests showed significant improvements in strength. Samples treated with both Bio-NS and FICP for 28 days achieved a maximum UCS of 4.28 MPa with 14.6% calcium carbonate content, representing an 11.17% increase in strength compared to control samples treated only with FICP. While the strength gain is incremental, the key advancement lies in demonstrating a single-organism, in situ process that eliminates mechanical mixing and external nanoparticle procurement required by existing methods. These findings demonstrate the potential of the hybrid bio-treatment to significantly enhance soil strength in situ, offering a promising, sustainable solution for geotechnical engineering applications.