Effects of palm fiber on soil detachment capacity of purple soil treated with enzyme-induced carbonate precipitation (EICP) in Three Gorges Reservoir Area

Purple soil represents a predominant soil type extensively found in the Three Gorges Reservoir Area (TGRA), where plagued by severe soil erosion, which is a critical environmental issue exacerbated by the soil's inherent properties and local topography. Soil erosion not only poses a formidable threat to the sustainable socio-economic development of the Yangtze River Economic Belt but also to the long-term ecological security and functional integrity of the reservoir itself. Previous studies have established that Enzyme-Induced Carbonate Precipitation (EICP), as a promising bio-cementation technique, significantly enhances soil strength and soil erosion resistance by catalytically generating cementitious calcium carbonate crystals which improve interparticle bonding, while the EICP-treated soil exhibits brittle failure characteristics. Although fiber incorporation significantly improves the brittleness of EICP-treated soil, the mechanism by which fibers influence the erosion resistance of EICP-reinforced soil remains unclear. To investigate the effect of palm fiber on the anti-detachment capacity of EICP-reinforced purple soil in the TGRA, this study used the purple soil from the TGRA as the test material. Experimental variables included fiber content (0 and 0.1%), cementation solution concentration (0.5, 1.0, 1.5, and 2.0 mol/L), and curing duration (1, 7, 15, 30, 60, and 120 d). Untreated purple soil served as the control group (CK). Simulated scouring tests were conducted to elucidate the mechanism of palm fiber’s influence on the soil detachment capacity of EICP-reinforced purple soil from the perspectives of apparent cohesion and calcium carbonate content, and the microscopic mechanism of the treatment was also analyzed. The results indicated that compared with the CK treatment, the soil detachment capacity of EICP-treated soil reduced by 25.97%-80.01%, which further decreased by 9.15%-48.98% after fiber incorporation. The apparent cohesion and calcium carbonate content of the EICP-treated group increased by 45.98%-123.41% and 10.29-28.60 times, respectively, when compared with the CK group, and they were further enhanced by 8.40%-29.31% and 7.04%-27.39%, respectively, after fiber incorporation, suggesting fiber incorporation promoted calcium carbonate crystal formation and enhanced apparent cohesion in EICP-treated soil. The improvement effect of the fibers on increasing the apparent cohesion and calcium carbonate content in EICP-treated soil were influenced by the curing duration and cementation solution concentration. Under the same cementation solution concentration, fiber incorporation increased apparent cohesion by 8.40%-12.66%, 20.94%-29.31%, 14.66%-19.54%, 14.30%-18.62%, 13.67%-17.73%, and 12.43%-16.50% for curing durations of 1, 7, 15, 30, 60, and 120 d, respectively, with the most significant improvement at 7 d, and increased apparent cohesion by 8.40%-20.94%, 9.66%-23.80%, 12.66%-29.31%, and 10.39%-25.13% for cementation solution concentrations of 0.5, 1.0, 1.5, and 2.0 mol/L, respectively, with the best effect observed at 1.5 mol/L under the same curing duration. Similarly, fiber incorporation increased calcium carbonate content by 7.04%-10.51%, 17.09%-27.39%, 13.07%-20.90%, 13.08%-21.31%, 13.01%-19.87%, and 12.75%-19.89% for curing durations of 1, 7, 15, 30, 60, and 120 d, respectively, with the most significant increase at 7 d, fiber incorporation increased calcium carbonate content by 7.04%-17.09%, 8.09%-20.23%, 10.51%-27.39%, and 8.40%-22.08% for cementation solution concentrations of 0.5, 1.0, 1.5, and 2.0 mol/L, respectively, with the best effect at 1.5 mol/L under the same curing duration. Apparent cohesion and calcium carbonate content both exhibited a highly significant exponential functional relationship with the soil detachment capacity of purple soil (P < 0.01). The results indicated that fibers incorporation further reduced the soil detachment capacity by increasing apparent cohesion and calcium carbonate content. Microscopic analysis indicates that fiber provide reaction site for the EICP, promoting the calcium carbonate crystals formation and enhancing the stability of the soil, thereby reducing the soil detachment capacity. This study confirmed that fiber incorporation further enhances the erosion resistance of EICP-treated purple soil in the TGRA, providing a theoretical basis for soil and water conservation in the region.