Improving settlement and reinforcement uniformity of marine clay in electro-osmotic consolidation using microbially induced carbonate precipitation

This study explored the effect of microbially induced carbonate precipitation (MICP), a natural bio-geotechnical process, on mitigating the uneven settlement in electro-osmotic consolidation of soft soil. The real-time drainage and settlement were measured, and the control behavior of drainage to settlement was discussed. MICP solution components were also selected as the different additives to determine the control mechanism of MICP in improving settlement and reinforcement uniformity of clay. After the tests, the chemical properties and microstructure were analyzed according to pH, conductivity, and SEM. The addition of MICP solution in clay significantly even reduced the coefficient of settlement variation by 53.2%, and the upper surface profile tended to be uniform. Contrary to control, the coefficient of settlement variation of MICP-treated soil decreased gradually with drainage volume, mainly due to the filling of solid substances such as calcium carbonate, biofilm, and/or calcium hydroxide produced within soil pores. MICP significantly improved the uneven soil reinforcement generated during the electro-osmotic consolidation but resulted in the lower strength near the anode due to the less drainage. The contribution of MICP solution components to the improvement of settlement and strength uniformity obviously varies. Bacterial cells improved the settlement uniformity but had no effect on the strength improvement of soil. The co-existence of Ca²⁺ and bacterial cells maximized the modification effect, which determined the production of mineral precipitation. Microstructure observation proved the formation of calcium carbonate. The results demonstrated that MICP is an effective technique to improve the settlement and reinforcement uniformity of marine clay in electro-osmotic consolidation.