Bio-VegeGrout for soil strength enhancement: effects of fermentation period on mechanical performance and microstructural characteristics

This study investigates the potential of fermented Bio-VegeGrout (BVG) as a sustainable grouting agent made from vegetable waste for improving the strength of clayey silt soil, highlighting its value in waste management. The waste vegetables were fermented for different periods (7 to 35 days) to evaluate the influence of fermentation duration on soil strength and microbial succession. Unconfined compressive strength (UCS) testing, scanning electron microscopy (SEM), pH and conductivity measurements, and bacterial community analysis based on 16S rRNA gene sequencing were conducted. Soil treated with 30-day fermented BVG liquid achieved the highest UCS of 0.55 ± 0.05 MPa, compared to 0.24 ± 0.09 MPa at 7 days. The untreated soil could not withstand the test and failed immediately, highlighting the strengthening effect of BVG treatment of any fermentation duration. SEM observations revealed denser particle aggregation and reduced spaces between soil particles in samples treated with longer fermentation periods. High-throughput sequencing demonstrated clear shifts in bacterial community composition across fermentation periods and after soil treatment. The strength enhancement is likely associated with organic-assisted stabilization through fermentation-induced physicochemical interactions, and improved interparticle bonding within the soil matrix. These findings demonstrate that vegetable waste-derived BVG can provide a sustainable approach for soil strengthening and circular waste utilization.