Enzyme-induced carbonate precipitation technique for reinforcing underwater sand bed: A feasibility study based on model tests

Enzyme-Induced Carbonate Precipitation (EICP) is an innovative technique to improve soil strength and reduce permeability. However, the use of EICP for reinforcing underwater sand beds remains largely unexplored. To advance EICP implementation in various geotechnical applications, this paper develops a model box system to investigate the effectiveness of the EICP technique in reinforcing underwater sand beds. An "injection-extraction" system is designed to facilitate the flow of the EICP solution through underwater sand layers. Key parameters, including conductivity, pH, and Ca 2+ concentration of the solution, are measured and analyzed. Electrical resistivity tomography (ERT) is utilized to evaluate the reinforcement effect in the underwater sand bed. The permeability of the model is tested to verify the feasibility of EICP technology for strengthening underwater sands. Furthermore, scanning electron microscope (SEM) is performed to investigate the growth mechanisms of calcium carbonate (CaCO 3 ) crystals. The results show that the permeability of the model decreases from 1.28 × 10 −2 m/s to 9.66 × 10 −5 m/s, representing a reduction of approximately three orders of magnitude. This verifies that the EICP technology can greatly reduce the permeability of underwater sand beds. With increasing grouting cycles, the resistivity of the underwater sand initially decreases and then increases. This variation in sand resistivity is significantly influenced by the ion concentration in the solution, resulting in marked differences in resistivity at various depths and positions within the sand. The findings from this study offer a theoretical basis for the application of EICP technology in reinforcing seabed foundations and supporting marine infrastructure such as offshore pipelines, wind turbines, and oil platforms.