Effectiveness of microbial-induced carbonate precipitation for mitigating the hydraulic erosion of the riverbank

Soil erosion and riverbank degradation pose major threats to ecosystem health and sustainable development of human society. The seemingly effective hard revetment structures have often overlooked the self-purification capacity of rivers. This study experimentally explored the effectiveness of microbial-induced carbonate precipitation (MICP) for mitigating the hydraulic erosion of riverbanks and permeability characteristics of bio-revetment. Erosion tests of MICP-treated sandy soil using the premixing-infiltration technique were conducted with a modified Erosion Function Apparatus (EFA). The erosion resistance of microbially premixed sandy soil did not exhibit the anticipated enhancement due to the limited quantity and ineffective cementation of CaCO₃ from the single-time premixed treatment. The erosion rate of the MICP-treated natural sand increased exponentially with the escalation of the flow shear stress. The critical shear stress for the sand treated with premixing and four rounds of infiltration increased by 105.9 times, and the erodibility coefficient decreased by 99.9% compared to the untreated group. This notable enhancement was attributed to the accumulation of effectively cemented CaCO₃ from repeated infiltrative consolidation treatments. A generalized power functional model was established to describe the relationship between the critical shear stress and CaCO₃ content. The permeability of the revetment was characterized to delineate the connectivity between the aquatic and terrestrial environments. The scanning electron microscopy (SEM) analysis revealed that sand particles and effectively cemented CaCO₃ at their contact points formed a skeleton-like structure, creating a novel sand-based material with both water permeability and erosion resistant. This bio-cementation method offers an innovative perspective for mitigating riverbank degradation.