Mechanical Properties of Fine-Grained Soils Treated with Fungal Mycelium of <i>Trichoderma virens</i>

Recent investigations into bio-mediated soil improvement have identified fungal mycelium as a promising candidate for innovative applications in geotechnical engineering. Fungal mycelia can increase soil water repellency, reduce hydraulic conductivity and increase matric suction by reducing pore size, and cement and bind soil particles together through biomineralization and extracellular polymeric substance (EPS). Previous studies, however, focused primarily on the effects of fungal mycelia on sandy soils. This study investigated the effects of the filamentous fungus Trichoderma virens (ATCC 9645) on mechanical properties of fine-grained soils. Three types of fine-grained soils were used in this study, including Baton Rouge (BR) silt, silica silt, and kaolinite. Unconfined compression, drying cake (DC), and Brazilian tensile strength (BTS) tests were conducted under different moisture contents to measure unconfined compressive strength (UCS), Young’s modulus, soil shrinkage curve, suction stress characteristic curve (SSCC), and tensile strength of untreated, potato dextrose broth (PDB)–treated, and fungal-treated specimens (PDB suspended with fungal mycelia). The results showed T. virens fungal mycelia increased the mean UCS and BTS of BR and silica silts at oven-dry condition by about 100% and 64%, respectively. T. virens fungal mycelia resulted in negligible improvement in the UCS of kaolinite, likely due to the constrained pore size that restricted fungal growth. The increases of UCS and BTS in BR and silica silts were attributed to the increase of suction stress magnitude (i.e., increase of attractive interparticle stress), resulting from the increased capillary and physicochemical forces by fungal mycelia.