# Recent Developments on Biomineralization for Erosion Control
## 5 Conclusions  
This paper comprehensively reviews recent advancements in MICP for erosion control and liquefaction mitigation in ocean engineering, synthesizing multi-scale experiments, field applications, and coupled numerical modeling. The efficacy of biomineralization in diverse scenarios, including coastal slope stabilization, local scour mitigation, and seabed reinforcement under wave actions, are evaluated systematically, and suggestions for future studies are also proposed. The specific conclusions are as follows:  
1. The optimization of reinforcement methodology (mixing, grouting, immersion) and material formulation (polycarboxylic acid, PA) are conducive to a more uniform distribution of calcium carbonate. The addition of 3% polycarboxylic acid (PA) delays the onset of CaCO\({}_{3}\) precipitation by >2 h and acts as a non-bacterial nucleation template, facilitating spatially uniform distribution. Kinetic analysis of Ca\({}^{2+}\) conversion confirmed complete ion utilization within 24 h under optimized PA concentration (3%), yielding a compressive strength of 2.76 MPa after five treatment cycles;
2. The erosion resistance of coastline soil was investigated by erosion function apparatus (EFA) tests, tidal actions model tests, wave actions model tests, and field applications. Field validations in Ahoskie and Sanya demonstrate the efficacy of MICP in coastal erosion control through tailored delivery systems and environmental adaptations. In Ahoskie, three delivery methods (surface spraying, PVDs, and trenches) achieved distinct performance: surface spraying formed 7% CaCO\({}_{3}\) crusts (73% improvement at surface compared to the untreated soil), PVDs enhanced subsurface layers (72% improvement at 30 cm depth compared to the untreated soil), and trenches concentrated CaCO\({}_{3}\) (9.9%) near gravel interfaces, collectively enabling the slope to withstand Hurricane Dorian over 331 days. Meanwhile, [PERSON]'s studies highlighted seawater-compatible MICP solutions, achieving maximum 1743 kPa penetration resistance in the atmospheric zone and layered \"M-shaped\" CaCO\({}_{3}\) precipitation in tidal regions. Comparatively, EICP under freshwater yielded weaker aggregates, with MICP's spherical crystals outperforming EICP's irregular structures. While tidal exposure degraded MICP durability, synergies between biomineralization and natural sedimentation underscored its ecological potential;
3. MICP coupled with polyvinyl alcohol (PVA) effectively mitigated local scour around the monopile through biomineralization and polymer-enhanced crystal adhesion. Experimental studies reveal that MICP treatments (2-4 cycles) reduce maximum scour depth by 84-100% under unidirectional currents through the formation of a 4-9 cm MICP cemented cone stabilizing seabed sediment. It is necessary to consider the balance of MICP protective times and edge scour. MICP coupled with polyvinyl alcohol (PVA) outperforms conventional methods, achieving 500-fold increases in critical shear stress (94.4 Pa) via dense vaterite crystallization at particle contacts and sustaining <0.3 mm erosion under extreme flows. Synergistic effects of polymer-modulated infiltration and biomineralization enable precise 5 cm-thick cemented layers without deep grouting;
4. In addition to erosion protection, MICP technology can also be used to reinforce the seabed and improve stability. The numerical model of MICP reaction for seabed reinforcement considering the wave actions, incorporating bacterial kinetics (suspended/attached phases), urea hydrolysis (Michaelis-Menten equation), and Darcy-driven convection-diffusion-reaction processes, can be used to analyze the seabed stability after MICP treatment. This framework accounts for CaCO\({}_{3}\)-induced porosity reduction and shear modulus enhancement, resolving wave-seabed-MICP interactions. Simulations reveal MICP increases seabed stability by amplifying vertical effective stress and reducing pore pressure.