# Recent Developments on Biomineralization for Erosion Control
## 3 Multi-Investigations of Biomineralization Erosion Control in Ocean Engineering
### Erosion Control of Coastline
transport solutions deeper into the soil, while trenches (60 cm long, 15 cm deep) with pea gravel backfill created localized high-strength zones. Dynamic cone penetration (DCP) tests post-treatment revealed a 73% reduction in surface (0-10 cm) for sprayed areas compared to the untreated soil, with a 2.5-14.5 cm crust containing 7% CaCO\({}_{3}\). PVDs enhanced deeper layers, achieving 48% surface and 72% subsurface (30 cm) improvements, while trenches exhibited concentrated strength gains near gravel interfaces, reaching 9.9% CaCO\({}_{3}\) content. Remarkably, the treated slope resisted erosion during Hurricane Dorian, maintaining integrity over 331 days due to the crust's durability and permeability retention, which supported natural vegetation recovery. As shown in Figure 2, the Sanya implementation expanded this research to tidal environments, comparing MICP and EICP performance under seawater and freshwater conditions. At Yazhou Bay, a coastal sandy slope was divided into atmospheric and tidal zones, treated using dual-nozzle sprayers for MICP (_Sporosarcina pasteurii_ cultures) or EICP (urease enzymes) developed by the authors with 1M-concentration urea-CaCl\({}_{2}\) solutions. Seawater-based solutions (34.9% salinity) were tested against freshwater variants to explore marine adaptability. Wind conditions near the site, measured approximately 2 m above the ground, exhibited considerable variability with speeds ranging from 0.53 to 17.55 m/s over one-minute intervals. Tidal elevations at the monitoring location fluctuated between 20 and 120 cm, and the local water depth varied from 3.8 to 5.8 m. Observed wave characteristics included significant heights of 0.2 to 0.3 m and wave periods ranging from 11 to 16 s. In the atmospheric zone, the MICP-treated zone by seawater achieved 1743 kPa penetration resistance (vs. 35-85 kPa in the untreated zone) with a 17 cm crust (9.9% CaCO\({}_{3}\)), reducing erosion by 0.197 m\({}^{3}\) compared to the untreated zone (0.393 m\({}^{3}\) loss). The EICP-treated zone by freshwater yielded lower but significant resistance, about 560 kPa (8.1% CaCO\({}_{3}\)). In tidal zones, wave and saltwater exposure degraded protection performance, and seawater-MICP peaked at 493 kPa but reverted to baseline within 24 days. However, tidal flow induced layered CaCO\({}_{3}\) deposition (\"M-shaped\" profile at 5-15 cm depth) and net sediment deposition (0.054-0.197 m\({}^{3}\) retention vs. untreated 0.29 m\({}^{3}\) erosion). Microstructural analysis via SEM highlighted spherical CaCO\({}_{3}\) crystals (5-20 \(\upmu\)m) in the MICP-treated zone, bridging sand grains, while EICP produced smaller, irregular aggregates [124]. These studies collectively demonstrate MICP's transformative potential in coastline erosion control through biomineralization, offering an eco-friendly alternative to conventional coastal protection methods when environmental requirements have to be considered. MICP \begin{table}
\begin{tabular}{p{42.7 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt}} \hline \hline
**Site** & **Treatment Method** & **Soil Type** & \
\begin{tabular}{c} **CaCO\({}_{3}\) Content and Distribution** \\ **Along Depth** \\ \end{tabular} &
\begin{tabular}{c} **UCS or** \\ **Penetration** \\ **Resistance** \\ \end{tabular} & **Reference** \\ \hline Ahoskie & Surface spraying & Poorly graded sand (SP) & \(\leq\)5.2\%, decreasing first and then decreasing & & Ghasemi and Montoya, 2022 \\ Ahoskie & Prefabricated vertical drains & Poorly graded sand (SP) & \(\leq\)4.9\%, increasing first and then decreasing & & Ghasemi and Montoya, 2022 \\ Ahoskie & Shallow trenches sand (SP) & Poorly graded sand (SP) & \(\leq\)4\%, decreasing & \(\leq\)150 kPa & Ghasemi and Montoya, 2022 \\ Sanya & Surface spraying & Sandy soil at atmospheric region & \(\leq\)10\%, decreasing first and then decreasing & & \\ Sanya & Surface spraying & Sandy soil at tidal region & \(\leq\)5\%, fluctuating & \(\leq\)500 kPa & [PERSON] et al., 2024 [125] \\ \hline \hline \end{tabular}
\end{table}