# Recent Developments on Biomineralization for Erosion Control
## 3 Multi-Investigations of Biomineralization Erosion Control in Ocean Engineering
### Stability Evaluation of MICP-Reinforced Seabed
The pore pressure \(p\) affects the Darcy velocity, thus affecting the convection-diffusion-reaction process and the precipitation of calcium carbonate. Conversely, the CaCO\({}_{3}\) precipitation clogs the pores, reduces permeability, and increases the shear modulus, which in turn affects Biot's dynamic response. Therefore, this MICP numerical model considering wave actions is a bidirectional coupled nonlinear system. It should be emphasized that the seabed is assumed to be uniform, isotropic, and infinitely deep. The bacteria themselves do not affect the porosity and permeability characteristics of the seabed, which are mainly controlled by the calcium carbonate generated by the MICP reaction. [PERSON] et al. (2023) first verified the correctness of this numerical model through unit tests and then carried out a large number of calculations [133]. As shown in Figure 5a,b, the MICP seabed reinforcement process includes four stages: (1) installation of grouting pipes and injection of bacterial solution (0-\(t_{1}\)); (2) injection of cementing solution (\(t_{1}\)-\(t_{2}\)); (3) MICP reaction phase (\(t_{2}\)-\(t_{4}\)), where urea and calcium are consumed and calcium carbonate precipitates, leading to increased strength and reduced porosity; and (4) wave impact phases--during (\(t_{3}\)-\(t_{4}\)) and after (\(t_{4}\)-\(t_{5}\)) the reaction. The coupled model, built in COMSOL Multiphysics v.5.0, solves PDEs via the finite element method with a backward difference scheme, incorporating interactions among flow, chemistry, and bacterial activity. Figure 6 outlines the simulation process, including geometry setup, parameter input, meshing, and transient analysis. Boundary conditions vary by stage: chemical inputs at the top boundary during injection phases,zero-flux or wave pressure conditions during reaction and wave-loading stages, and rigid, impermeable conditions at the seabed base throughout. Several limitations in the current model are acknowledged, such as the exclusion of biofilm degradation and the simplified treatment of soil variability. The FEM approach also struggles to capture the actual particle morphology and gradation, affecting simulation accuracy for bacterial and solute transport. These simplifications were made to balance model complexity with computational feasibility. Nonetheless, this review highlights recent progress in enhancing MICP efficiency, erosion resistance, and large-scale applications under marine conditions. Future studies will aim to integrate more realistic bio-chemo-mechanical processes. \[\frac{\partial C_{bacl}}{\partial t}=-k_{\text{att}}C_{bacl}-k_{\text{d}}C_{ bacl} \tag{5}\]1 Liquefaction mitigation of seabed: (**a**) schematic diagram, (**b**) complete stage of MICP-treated seabed, and (**c**) the flowchart for judging the instability of MICP-treated seabed [133; 134]. The results showed that the MICP process increased the excess pore pressure gradient and vertical effective stress amplitude of the seabed (Figure 6a). This is mainly due to the blockage of the seabed surface soil by the precipitation of calcium carbonate, which makes it bear greater seepage force. As shown in Figure 6b, the maximum instability depth of the untreated seabed increases with the increase in the wave height. If cohesive force \(F_{\mathrm{c}}\) is ignored, the MICP-treated seabed started to be unstable when the wave height reached 2 m. When the inner cohesive force \(F_{\mathrm{c}}\) is considered, the seabed remained stable under a 4 m wave height. These results indicate that MICP plays a vital role in keeping the seabed stable under the wave actions.