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

Purple soil can represent a predominant soil type extensively found in the Three Gorges Reservoir Area (TGRA). Severe soil erosion has also caused environmental problems in the soil properties and local topography. Particularly, the sustainable socio-economic development of the Yangtze River Economic Belt is closely related to the long-term ecological security and functional integrity of the reservoir. Fortunately, the Enzyme-Induced Carbonate Precipitation (EICP) can be expected to serve as a promising bio-cementation technique. The soil strength and erosion resistance can be significantly enhanced to catalytically generate the cementitious calcium carbonate crystals for the high interparticle bonding. While the EICP-treated soil has exhibited brittle failures. Although the fiber incorporation significantly improves the brittleness of the EICP-treated soil, it is often required for the fiber influence on the erosion resistance of the EICP-reinforced soil. This study aims to investigate the effect of the palm fiber on the anti-detachment capacity of the EICP-reinforced purple soil in the TGRA. The test material was taken from the purple soil from the TGRA. Experimental variables included the 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 clarify the influence mechanism of the palm fiber on the soil detachment capacity of the EICP-reinforced purple soil, particularly from the perspectives of the apparent cohesion and calcium carbonate content. The microscopic mechanism of the treatment was also analyzed after measurement. The results indicated that the soil detachment capacity of the EICP-treated soil was reduced by 58.63%, compared with the CK treatment, which further decreased by 25.81% after fiber incorporation. The apparent cohesion and calcium carbonate content of the EICP-treated group increased by 79.73% and 20.58 times, respectively, compared with the CK group, which were further enhanced by 16.50% and 16.01%, respectively, after fiber incorporation. The fiber incorporation promoted the calcium carbonate crystal formation and apparent cohesion in the EICP-treated soil. The curing duration and cementation solution concentration were attributed to the increasing apparent cohesion and calcium carbonate content in the EICP-treated soil. Under the same cementation solution concentration, the fiber incorporation increased the apparent cohesion for different incubation time. The apparent cohesion also increased for the cementation solution concentrations of 0.5, 1.0, 1.5, and 2.0 mol/L, where the best performance was observed at 1.5 mol/L under the curing duration of 7 d. Similarly, the fiber incorporation increased the calcium carbonate content for the curing durations of 1, 7, 15, 30, 60, and 120 d, respectively. The fiber incorporation increased the calcium carbonate content for the cementation solution concentrations of 0.5, 1.0, 1.5, and 2.0 mol/L, with the best effect at 1.5 mol/L under the curing duration of 7 d. Both apparent cohesion and calcium carbonate content exhibited a highly significant exponential function with the soil detachment capacity of the purple soil (P < 0.01). The fiber incorporation further reduced the soil detachment capacity to increase the apparent cohesion and calcium carbonate content. Microscopic analysis indicated that the fiber provided the reaction site for the EICP, in order to promote the calcium carbonate crystals formation and the stability of the soil, thereby reducing the soil detachment capacity. This fiber incorporation further enhanced the erosion resistance of the EICP-treated purple soil in the region. The finding can also provide a theoretical basis for soil and water conservation in the TGRA.