Recent Developments on Biomineralization for Erosion Control

Abstract

Erosion poses significant threats to infrastructures and ecosystems, exacerbated by climate change-driven sea-level rise and intensified wave actions. Microbially induced calcium carbonate precipitation (MICP) has emerged as a promising, sustainable, and eco-friendly solution for erosion mitigation. This review synthesizes recent advancements in optimizing biomineralization efficiency, multi-scale erosion control, and field-scale MICP implementations in marine dynamic conditions. Key findings include the following: (1) Kinetic analysis of Ca²⁺ conversion confirmed complete ion utilization within 24 h under optimized PA concentration (3%), resulting in a compressive strength of 2.76 MPa after five treatment cycles in ISO-standard sand. (2) Field validations in Ahoskie and Sanya demonstrated the efficacy of MICP in coastal erosion control through tailored delivery systems and environmental adaptations. Sanya’s studies highlighted seawater-compatible MICP solutions, achieving maximum 1743 kPa penetration resistance in the atmospheric zone and layered “M-shaped” CaCO₃ precipitation in tidal regions. (3) Experimental studies revealed that MICP treatments (2–4 cycles) reduced maximum scour depth by 84–100% under unidirectional currents (0.3 m/s) with the maximum surface CaCO₃ content reaching 3.8%. (4) Numerical simulations revealed MICP enhanced seabed stability by increasing vertical effective stress and reducing pore pressure. Comparative analysis demonstrates that while the destabilization depth of untreated seabed exhibits a linear correlation with wave height increments, MICP-treated seabed formations maintain exceptional stability through cohesion-enhancing properties, even when subjected to progressively intensified wave forces. This review supports the use of biomineralization as a sustainable alternative for shoreline protection, seabed stabilization, and offshore foundation integrity.

1. Introduction

In ocean geotechnical engineering, erosion is an inevitable problem, the most typical of which includes coastal erosion, local scour around piles, and increased erosion caused by seabed liquefaction. Coastal erosion, driven by sediment transport imbalances under wave and flow dynamics, poses a global threat to land resources and infrastructures. It has been reported that the total coastal area (including houses and buildings) lost in Europe due to marine erosion is estimated to be about 15 km² per year [1]. Approximately 86% of East Coast beaches in the United States have undergone erosion during the last 100 years [2]. Between 1984 and 2015, erosion claimed 28,000 km² of land worldwide, with the eastern shoreline of England expected to retreat by 20 m in the coming years. At present, Europe experiences a coastal loss of about 15 km² each year from erosion. The annual cost of mitigation measures is estimated to be about 3 billion euros per year in Europe [1]. Mid-century forecasts based on RCP 4.5 and RCP 8.5 scenarios estimate global mean long-term shoreline shifts (dxshore, LT) with 90% confidence intervals between −78.1 and −1.1 m for RCP 4.5, and −98.1 to 0.3 m for RCP 8.5, both reflecting predominantly erosional patterns [3]. Coastal erosion affects a significant share of global shorelines [4,5], becoming a more pressing concern due to the dense human populations and diverse productive uses concentrated along these coastal zones [6]. In addition, under the action of current, the horseshoe vortex and wake vortex will appear around the pile foundation because of the hindering effect. The horseshoe vortex interacts strongly with the seabed soil, increasing the local shear stress, causing the soil particles to start and migrate, while the wake vortex forms a negative pressure zone, making it easier for the soil particles below to start and migrate [7,8,9,10,11,12]. The results of Raudkivi and Ettema (1983) show that the scour depth under the static bed condition is related to the median particle size, particle size distribution, the ratio of water depth to pile diameter, and the ratio of water depth to soil particle size, where the ultimate equilibrium scour depth given is about 2.3 times the pile diameter [13]. For the living bed condition, many researchers believe that the ultimate equilibrium scour depth can be taken as 1.3 times the pile diameter [14]. Scour will reduce the buried depth of the pile foundation, increase the eccentricity of the horizontal load, and affect the stress history of the remaining soil, greatly weakening the horizontal bearing capacity of the pile foundation [15,16]. The wave-induced excess pore pressure response of the seabed will also cause the seabed soil to completely or partially liquefy, resulting in the weakening or even loss of bearing capacity. Wave-induced seabed liquefaction includes transient liquefaction and residual liquefaction. The transient pore pressure response is the periodic pulsation of pore water pressure in the seabed caused by cyclic wave actions. In the trough, the transient pore pressure has an upward pressure gradient, which generates seepage in the soil. When the seepage force is greater than the weight of the soil particles, transient liquefaction will occur in the soil [17,18,19,20,21,22]. The cumulative pore pressure response, also known as the residual pore pressure response, is the effect of the growth of pore water pressure over time due to soil skeleton compression and poor drainage under cyclic wave pressure. Under the continuous actions of the wave, the residual pore pressure of the soil may continue to rise. When the excess pore pressure exceeds the effective stress of the overlying soil, the cumulative liquefaction occurs [23,24,25,26].

Billions of dollars have been invested in erosion or liquefaction defenses in ocean engineering, including riprap, seawalls, breakwaters, fluidized solid soil, beach nourishment, and mangrove afforestation [27,28,29,30,31,32,33,34,35]. While seawalls and breakwaters effectively reduce the loss of coastal soil and offer long service life, they can cause secondary erosion. The construction of these structures requires significant amounts of concrete, which not only causes a large amount of carbon emissions, but also forms a permanent cementation on the beach, threatening the normal growth and activities of organisms. Riprap and beach nourishment, while avoiding environmental pollution, require ongoing maintenance. The long plant growth cycle of mangrove afforestation also needs to be considered, although this technology comes from nature. In general, these conventional approaches, while protective, can be costly and environmentally damaging when considering material, energy, time, cost, and environmental impact. Therefore, it is very meaningful to seek sustainable and environmentally friendly methods to prevent coastal erosion of sandy slopes and liquefaction of the seabed.

Drawing inspiration from the natural soil diagenesis process mediated by bacteria, microbially induced calcium carbonate precipitation (MICP) presents a novel method to enhance the engineering properties of sand while offering notable environmental advantages over conventional reinforcement techniques. This process utilizes urease-producing bacteria, such as Sporosarcina pasteurii, which hydrolyze urea and precipitate calcium carbonate in the presence of calcium ions. The resulting CaCO₃ strengthens the sand by bonding particles, clogging pores, and coating grains, thereby improving its strength, stiffness, and resistance to erosion [36]. MICP offers benefits such as controllable reactions, eco-friendliness, and low carbon emissions. The bacterial solution (BS) and cementing solution (CS) used in MICP have very low viscosities, allowing them to penetrate farther and deeper compared to Portland cement and other chemical agents. Moreover, the calcium carbonate generated by MICP does not fully occlude the pores, which supports biological processes and promotes plant growth [37,38,39,40,41,42,43,44,45,46,47]. Additionally, MICP is highly suitable for marine environments due to the alkaline pH conditions and the alkaliphilic nature of Sporosarcina pasteurii. Furthermore, the presence of calcium and magnesium ions in seawater enhances the rate of carbonate precipitation [48,49]. Since the discovery by Boquet et al. (1973) that certain microorganisms can induce calcium carbonate precipitation via their metabolic processes, research on the reaction mechanisms and engineering applications of MICP has been continuously advancing worldwide [50]. The National Research Council of the United States has recognized MICP technology as a key research focus for the 21st century. Whiffin (2004) was the first to utilize MICP for reinforcing loose sand, enhancing its strength and stiffness [51]. Later, Michell and Santamarina (2005) highlighted the wide-ranging applications and significant potential of MICP in engineering [52].

To date, MICP technology has been widely used in the fields of ground improvement [53,54,55,56,57,58,59,60,61,62,63,64,65], erosion control [45,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81], crack repair [82,83,84,85,86,87], liquefaction mitigation [88,89,90,91,92,93,94,95,96,97], corrosion protection [98,99], etc. There are a large number of review articles that have comprehensively summarized MICP from the aspects of technical principles, influencing factors, application scenarios, and reinforcement efficiency [100,101,102,103,104,105,106,107,108,109,110], but there has been no comprehensive review of MICP technology in ocean engineering. Unlike previous reviews focusing on land-based applications, this work evaluates MICP performance in oceanic environments subject to wave and tidal loads. Therefore, this review focuses on erosion and liquefaction control in the field of ocean engineering and conducts a comprehensive analysis from the traditional biomineralization process, optimization, erosion control of coastline, local scour protection around monopile, and stability evaluation of the MICP-treated seabed. Through an in-depth discussion of key points, comments and suggestions on current research gaps and potential future steps are provided. It would be helpful to more clearly articulate the challenges of applying MICP in coastal and offshore settings (for example, biofilm stability in saltwater, treatment uniformity in submerged conditions).

2. Biomineralization Process and Efficiency Optimization

2.1. Traditional Biomineralization Process

The traditional biomineralization process, particularly MICP, leverages the metabolic activity of ureolytic bacteria, most notably Sporosarcina pasteurii, to precipitate calcium carbonate (CaCO₃) in porous media [111]. This process involves two critical biochemical reactions:

(1) Ureolysis: Sporosarcina pasteurii hydrolyzes urea into ammonium (NH₄⁺) and carbonate ions (CO₃²⁻) via the enzyme urease:

$$\mathrm{C}\mathrm{O}{\left(\mathrm{N}{\mathrm{H}}_2\right)}_2+2{\mathrm{H}}_2\mathrm{O}\stackrel{bacteria}{\to }2{\mathrm{N}\mathrm{H}}_4^{+}+{\mathrm{C}\mathrm{O}}_3^{2-}$$

(1)

(2) Calcium carbonate precipitation: The generated CO₃²⁻ reacts with free calcium ions (Ca²⁺) to form calcium carbonate:

$${\mathrm{C}\mathrm{O}}_3^{2-}+{\mathrm{C}\mathrm{a}}^{2+}\to {\mathrm{C}\mathrm{a}\mathrm{C}\mathrm{O}}_3\downarrow$$

(2)

These reactions occur optimally at pH 7–9, driven by bacterial mineralization capacity and site-specific geochemical conditions. The CaCO₃ crystals nucleate heterogeneously on microbial cell walls or sediment particles, progressively cementing soil grains and filling pore spaces [112]. Whiffin (2004) found that the optimal pH value for urease activity in bacterial solution containing bacterial cells is 9. pH controls the deposition rate, yield, and morphology of calcium carbonate by affecting the concentration of ammonium, carbonate, and bicarbonate ions in the porous medium solution. When the supersaturated concentration of the reaction ions (calcium ions and carbonate ions) is higher, the formation rate of calcium carbonate is faster and the crystals are smaller [51]. Studies have shown that there is an optimal pH range [113,114]. With the increase in pH, urease activity first increases and then decreases. Generally, calcium carbonate content and uniaxial compressive strength also show a trend of first increasing and then decreasing. However, compressive strength is related to factors such as ambient temperature, sand type, and pore distribution. The exact change in strength cannot be strictly determined based on the change of a single pH value.

The efficiency of biomineralization hinges on microbial metabolic activity, substrate availability, and environmental adaptability. Urease activity directly correlates with reaction kinetics. For instance, Sporosarcina pasteurii (S. p.) exhibits urease activity with a V_max of 3.55 mM urea hydrolyzed min⁻¹·mg⁻¹ at pH 7.0 and 25 °C under optimal aerobic conditions, demonstrating significantly faster microbiological CaCO₃ precipitation compared to chemical processes. While S. p. is capable of ureolysis under both aerobic and anaerobic conditions, the presence of oxygen enhances bacterial growth and enzyme expression, thereby improving biomineralization efficiency [115]. At present, a large number of calcium carbonate sediments have been found in the ocean environment, from coastlines to seabed sediments; they generally come from organic life forms such as corals and show obvious biological characteristics [49,116]. They interact with the complex ocean environment through the mineralization of urease-producing microorganisms in the coastlines and seabed and eventually precipitation. This type of sediment preserves good strength characteristics and porosity, providing an excellent shelter for the survival of organisms on coastlines and the seabed. However, it should be noted that under natural conditions, the formation of carbonate precipitation generally takes a long time, which mainly depends on the urease activity of bacteria, reactant concentration, temperature, humidity, oxygen, and other conditions. Especially in the ocean environment, how to intensify the process of biomineralization through artificial intervention and form technology that is beneficial to us is a question worth considering. In addition, the bacterial survival in seawater is also a limitation that hinders application.

2.2. Biomineralization Efficiency Optimization

One of the major issues that needs to be solved in the application of MICP technology is the uniformity of cementation. Uneven cementation will lead to stress concentration and brittle failure of the reinforced ground when subjected to load. Many scholars have conducted research and analysis on this issue. As shown in

Table 1. The soil reinforcement effects under different MICP treatment methods.

Treatment Method	Soil Type	CaCO3 Content and Distribution	UCS	Pros and Cons	Reference
Mixing	Silt	8~10%, relatively uniform	801.25 kPa	Good uniformity, suitable for shallow reinforcement, difficult to use on large areas	Kang et al., 2025 [117]
Grouting	Silt	5~13%, longitudinal inhomogeneity	684.78 kPa	Suitable for deep reinforcement with limited reinforcement range	Kang et al., 2025 [117]
Immersion	Silt	6~13%, radial inhomogeneity	206.11 kPa	Good uniformity, not suitable for field applications	Kang et al., 2025 [117]
One-phase injection method with 3% PA added	ISO-standard sand (GB/T 17671-1999) [119]	7~7.5%, relatively uniform	2.76 MPa	Good uniformity, suitable for large-scale field applications	Zhu et al., 2025 [118]

, three methodologies were evaluated by Kang et al. (2025) for MICP in silt cementation [117]. The mixing method, involving direct blending of bacterial and cementation solutions with silt prior to compaction, achieved optimal uniformity and strength (801.25 kPa UCS). This approach ensured even radial and longitudinal CaCO₃ distribution, effectively minimizing pore volume disparities. In contrast, the grouting method utilized pressure-driven injection, resulting in longitudinal inhomogeneity with declining CaCO₃ content (bottom-to-top gradients) and reduced strength (684.78 kPa UCS), attributed to pore channel clogging hindering upward slurry migration. The immersion method, which soaked silt in solutions, exhibited radial inhomogeneity as CaCO₃ precipitation decreased from outer to inner layers due to limited permeability, yielding the lowest strength (206.11 kPa UCS). While adjusting grouting pressure, solution concentration, or utilizing intermittent injection cycles could enhance solute distribution, the study identified mixing as the most effective strategy for uniform cementation. Structural analyses confirmed that mixing generated homogeneous pore networks with spatially consistent CaCO₃, whereas grouting and immersion produced strength variations dictated by solute transport limitations and gradient-dependent precipitation patterns. In addition to methodology optimization, material formulation can also be optimized. Zhu et al. (2025) developed a novel one-phase injection method integrated with polycarboxylic acid (PA) to optimize the uniformity and strength of MICP-treated sand [118]. By leveraging PA’s dual functionality, delaying CaCO₃ nucleation through Ca²⁺ chelation and acting as a non-bacterial nucleation template, this approach allows deeper penetration of solutions into pores before precipitation begins. Experiments demonstrated that 3% PA delayed initial CaCO₃ precipitation by over 2 h, enabling uniform reactant distribution, while calcium ion conversion rate curves confirmed complete Ca²⁺ utilization within 24 h under optimal conditions (3% PA added), achieving a strength of 2.76 MPa after five treatment cycles. Comparative analyses revealed PA-MICP’s superiority over traditional methods like grouting and immersion, which suffered from pore clogging and radial heterogeneity. The efficacy of PA shows progressively enhanced homogeneity and cementation coverage with increasing PA concentrations (0%, 1%, 3%, 5%) and extended treatment times, ultimately validating PA’s role in bridging soil particle gaps for structural reinforcement. Yet, the impacts of ambient environmental conditions (such as temperature, salinity, oxygen availability, etc.) on optimization strategies should be further investigated.

3. Multi-Investigations of Biomineralization Erosion Control in Ocean Engineering

3.1. Erosion Control of Coastline

MICP technology has gradually been applied in the field of erosion control of coastline. Many scholars have systematically evaluated the erosion resistance of MICP-treated sand through unit tests, model tests, and field verifications. According to Clarà Saracho et al. (2020) [120], the erosion resistance of two-layer sand (a filter-soil layer consisting of 25 mm of silica sand (d₅₀ = 1.61 mm) overlying a base soil layer consisting of 25 mm of silica sand (d₅₀ = 0.21 mm)) treated with MICP was systematically evaluated using an erosion function apparatus in Cambridge. Untreated sand exhibited rapid surface erosion under tangential flow, with cumulative height loss escalating linearly under incremental shear stress. In contrast, MICP-treated sand (0.02 M urea–calcium solution) demonstrated reduced cumulative erosion by up to 90% due to calcium carbonate crystal cementation. X-ray computed tomography revealed that calcium carbonate filled pore space and formed inter-particle bridges, diminishing erodibility by altering the failure mechanism from particulate detachment to block erosion. Higher cementation concentrations (0.04~0.1 M urea–calcium solution) promoted larger, lognormally distributed crystals (up to 210 µm diameter), which enhanced aggregate stability. This microstructural evolution—linked to microbial metabolism and size-dependent crystal growth—significantly improved macro-scale resistance. The non-monotonic trend declines in erodibility (κ_d) with increased calcium carbonate content, underscoring MICP’s potential in stabilizing vulnerable interfaces in dams or offshore reservoirs. Future optimizations could target crystal uniformity and injection protocols to maximize erosion control while balancing permeability retention.

At the model scales, slope erosion tests during tidal actions were conducted by Salifu et al. (2016) [121]. Sandy soil was sourced from Troon Beach in Ayrshire, UK and air dried in the laboratory. Untreated natural sandy slopes subjected to tidal cycles rapidly collapse to their angle of repose (35°), losing ~0.2° per tidal event. However, MICP-treated slopes (using Sporosarcina pasteurii and 0.7 M CaCl₂–urea) resisted collapse by forming a bio-cemented crust (118~155 kg CaCO₃/m³). At 35° inclinations, treatment reduced erosion significantly, while steeper 53° slopes showed negligible erosion despite high shear stresses. The mechanism stems from urea hydrolysis-driven calcite precipitation, forming a bio-cemented crust that withstood tidal shear stresses. SEM and penetration tests confirmed that calcite bridges increased interparticle friction and cohesion. Afterwards, slope erosion tests during wave actions were also conducted by Kou et al. (2020) [122]. The sand used in the experiments featured a median particle size (D₅₀) of 0.71 mm and a specific gravity of 2.65. The physical model of the coastal sandy slope measured 60 cm in width and 20 cm in length, with three different heights tested—3.5 cm, 7.4 cm, and 14 cm—to simulate various slope conditions. Corresponding slope angles examined in the tests were 10°, 20°, and 35°. The sand slopes were characterized by an initial void ratio of 0.82, a relative density of approximately 51.4%, and an effective internal friction angle of 34°. Wave actions on untreated sandy slopes induced rapid particle detachment, forming bilinear erosion profiles. MICP treatment (four cycles of 0.5 mL/cm² bacterial and cementation solutions) reduced erosion rates by up to 97%, with calcium carbonate content correlating inversely with mass loss. Penetration resistance (up to 60 kN/m²) and SEM analyses revealed calcium carbonate’s dual role: nano-crystals filled pores, while macroscale aggregates (100–240 µm) formed load-bearing networks. Notably, higher treatment cycles (e.g., four cycles) yielded 30.1% CaCO₃ content, reducing erosion rates to <1 mm/h under wave velocities of 0.4 m/s. The nonlinear relationship between treatment cycles and erosion resistance highlights a threshold (beyond ~0.08 M Ca²⁺) where excessive crystal size may paradoxically weaken cohesion. The erosion rate of bio-cemented sandy slope R_e, which represents the erosion resistance, also shows a linearly increasing trend with the increase in the treatment cycle N because of the CaCO₃ formed. In order to more accurately simulate wave breaking on the coastline and analyze the erosion resistance of MICP-reinforced slopes, a series of large-section flume tests were carried out by Li et al. (2020a) [123]. The tested Fujian sand is characterized by a mean particle diameter (d₅₀) of 0.17 mm and a specific gravity of 2.633. Its gradation parameters include a uniformity coefficient of 1.57 and a curvature coefficient of 0.96, indicating relatively poor sorting. The material exhibits a range of void ratios, with minimum and maximum values recorded at 0.607 and 0.952, respectively. The experiments evaluated erosion patterns, penetration resistance, CaCO₃ distribution, and pore water pressure under varying MICP treatment cycles (zero, two, four) and wave heights (8, 10, 12 cm). The results show that four MICP treatments formed a robust cementation layer on the sandy slope, eliminating visible erosion after 60 min of wave action (Figure 1). The maximum erosion depths on the slope under the untreated slope, the two-times MICP-treated slope, and the four-times MICP-treated slope are 6 cm, 5 cm, and 0 cm, respectively. Penetration resistance increased dramatically from 0.14 MPa (untreated) to 2.04 MPa (four-times treated), linked to surface CaCO₃ content reaching 7% via acid washing tests. The calcium carbonate content of the MICP-treated area decreases from the toe to the top of the slope because the bacterial and cementation solutions flow from the top to the toe due to gravity. With the increase in MICP treatment times, the permeability of the slope is gradually decreased, resulting in difficult infiltration of the bacterial solution, cementation solution, and oxygen. Therefore, the difference in the bacterial solution, cementation solution, and oxygen content between the deep and the shallow layer of the slope is increased, leading to the increased difference in calcium carbonate content. MICP treatments form CaCO₃ crystals between sand particles, reducing permeability and restricting water pressure transfer. Consequently, Figure 1c shows thickened excess pore water pressure gradients in the surface layers of treated slopes compared to untreated ones, highlighting limited fluid mobility.

Some field implementations were also conducted to evaluate the erosion resistance of coastline slopes treated by MICP (

Table 2. The typical field implementations of coastal reinforcement.

Site	Treatment Method	Soil Type	CaCO3 Content and Distribution Along Depth	UCS or Penetration Resistance	Reference
Ahoskie	Surface spraying	Poorly graded sand (SP)	≤5.2%, decreasing, increasing first and then decreasing	≤420 KPa	Ghasemi and Montoya, 2022 [124]
Ahoskie	Prefabricated vertical drains (PVDs)	Poorly graded sand (SP)	≤4.9%, increasing, increasing first and then decreasing	≤150 kPa	Ghasemi and Montoya, 2022 [124]
Ahoskie	Shallow trenches	Poorly graded sand (SP)	≤4%, decreasing	≤150 kPa	Ghasemi and Montoya, 2022 [125]
Sanya	Surface spraying	Sandy soil at atmospheric region	≤10%, decreasing, increasing first and then decreasing	≤1800 kPa	Li et al., 2024 [125]
Sanya	Surface spraying	Sandy soil at tidal region	≤5%, fluctuating	≤500 kPa	Li et al., 2024 [125]

). The Ahoskie study focused on a sandy slope with poor grading, employing three MICP delivery methods: surface spraying, prefabricated vertical drains (PVDs), and shallow gravel-packed trenches [124]. Surface spraying applied urea–CaCl₂ solutions twice daily via an irrigation system with 25 nozzles, forming a uniform surface crust through sequential bacterial solution and cementation solution cycles over 14 days. PVDs (30 cm depth) facilitated vertical seepage, leveraging gravity to 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% CaCO₃. 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% CaCO₃ 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–CaCl₂ 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% CaCO₃), reducing erosion by 0.197 m³ compared to the untreated zone (0.393 m³ loss). The EICP-treated zone by freshwater yielded lower but significant resistance, about 560 kPa (8.1% CaCO₃). 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 CaCO₃ deposition (“M-shaped” profile at 5–15 cm depth) and net sediment deposition (0.054–0.197 m³ retention vs. untreated 0.29 m³ erosion). Microstructural analysis via SEM highlighted spherical CaCO₃ crystals (5–20 μm) 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 has the potential to be environmentally friendly, as it utilizes naturally occurring bacteria and produces calcium carbonate without harmful byproducts. However, in ecologically sensitive areas such as intertidal zones, careful evaluation is needed to avoid disrupting local habitats or altering water chemistry. Factors such as microbial strain selection, nutrient dosing, and byproduct control should be tailored to minimize ecological impact. Future studies will address these considerations through site-specific risk assessments.

3.2. Local Scour Protection Around Monopile

This section summarizes the local scour protection around a monopile treated by MICP. Li et al. (2022b) investigated the efficacy of MICP for mitigating local scour around monopile foundations under unidirectional currents with an average velocity of 0.1 m/s, 0.2 m/s, and 0.3 m/s [126]. The experiments were conducted in a large-scale flume using silica sand (d₅₀ = 0.16 mm) treated with MICP technology. The height and diameter of the model pile in the test are 0.84 m and 0.11 m. MICP treatments involved sequential spraying of bacterial solution (OD600 = 2.0, urease activity = 20 U/mL) and cementation media (1M urea/1M CaCl₂) 1–4 times over 4 days. For comparison, traditional riprap protection (5–10 mm gravel) was also tested. A non-contact camera system and handheld 3D scanners monitored scour evolution and post-test topography. Sediment transport rates were calculated using acid-washed CaCO₃ content and SEM analysis. As shown in Figure 3 and Figure 4, two-times MICP treatments reduced maximum scour depth (S_end/D_p) by 84% (from 1.14 D_p in untreated sand to 0.18 D_p), four-times treatments eliminated visible scour holes under 0.3 m/s live-bed conditions, while riprap protection achieved only 0.38 D_p. The D_p represents the diameter of the monopile. Penetration resistance increased exponentially with treatment cycles N. Surface CaCO₃ content reached 3.8%, forming an inverted cone-shaped cemented layer (height = 4–9 cm) that resisted downflow and horseshoe vortices. Sediment transport rate dropped by 53% (from 19.4 kg/m/h to 9 kg/m/h at pile proximity), attributed to CaCO₃ bridging effects (spherical crystals, 5–20 μm). However, the maximum edge scour depth (length) increases from 0.19 (3.18) D_p to 0.29 (4.36) D_p after two-times to four-times MICP treatments. It is necessary to consider the balance of MICP protective times and edge scour. To mitigate this, ensuring the treated area remains flush with the surrounding seabed helps reduce flow disturbance. Additionally, expanding the treatment area provides a buffer zone that dissipates shear forces. Incorporating gradual transitions or overlapping treatments further minimizes hydraulic gradients at the edges. These strategies enhance interface stability and reduce localized erosion. Zhu et al. (2024) investigated the lateral response of offshore monopiles reinforced by MICP through static and cyclic loading tests [127]. Key findings reveal that precast bio-reinforcement (4 D_p width and 1 D_p depth) enhances the lateral bearing capacity by 50% and reduces maximum bending moments by 25%, transitioning failure modes from localized to global overturning. Under cyclic loading, accumulated deformation decreased by 30–60% for one-way loading, with secant stiffness ratios (MICP-treated vs. untreated) ranging from 1.65–2.82 (higher under smaller loads). Mechanistically, MICP-treated sand improved shallow soil resistance, but stiffness evolution was governed by three competing factors: untreated sand compaction, bio-cementation degradation at low strains, and soil subsidence around the reinforced zone. The low-pH grouting method demonstrated eco-friendly advantages over traditional cementation, offering a sustainable solution to optimize monopile dimensions for offshore wind turbines while balancing cyclic durability and environmental impact.

Separately, Wang et al. (2020) evaluated the erosion protection effectiveness of polyvinyl alcohol (PVA) coupling MICP technology for bridge pier local scour through scale model flume experiments [128]. A 3D-printed pier model (12×3×16 cm) was embedded in PVA–MICP-treated Ottawa sand stratum and subjected to 20 h continuous flow simulation at 0.15 m/s (70% of untreated sand’s critical velocity). The results demonstrated that untreated sand developed a 25 mm horseshoe-shaped scour hole stabilizing within 2 h, while PVA coupling MICP-treated seabed maintained minimal erosion (<0.3 mm) with structural integrity. Microscopic characterization (SEM/XRD) revealed that PVA viscosity modulation facilitated dense distribution of 2–3 μm vaterite-type CaCO₃ crystals at particle contacts, significantly enhancing interlayer cementation strength. Erosion function apparatus (EFA) quantification showed modified sand exhibited 500-fold increased critical shear stress (94.4 Pa vs. 0.18 Pa for untreated sand), sustaining a low erosion rate (0.1 mm/h) under extreme 6 m/s flow velocity. Structure from Motion (SfM) topographic reconstruction confirmed over 95% reduction in sediment loss from treated zones, demonstrating that PVA’s delayed infiltration effectively controlled cementation layer thickness (~5 cm) through single-surface application without deep grouting.

MICP and PVA coupling MICP effectively mitigate local scour around the monopile through biomineralization and polymer-enhanced crystal adhesion. Their success hinges on controlled reagent, optimized treatment cycles, and geometric design to balance erosion resistance and edge scour.

3.3. Stability Evaluation of MICP-Reinforced Seabed

In addition to erosion protection, MICP technology can also be used to reinforce the seabed and improve stability. Considering the high cost and control difficulty of the physical experiments, numerical simulation was first developed for analysis. To date, numerical studies on MICP reaction are mainly based on the convection–diffusion–reaction theory and seepage framework in porous media. Martinez et al. (2014) used the first-order kinetic equation to establish a reaction model of urea hydrolysis and calcium carbonate precipitation but ignored the effect of calcium carbonate precipitation on the evolutions of porosity and permeability [129]. Fauriel and Laloui (2012) as well as Wang and Nackenhorst (2020) established a bio-chemo-hydro-mechanical model for MICP reaction and a bio-chemo-hydro model considering the concept of effective porosity, respectively [130,131]. Recently, a bio-chemo-hydro-mechanical model of transport, strength, and deformation for bio-cementation applications was developed by Bosch et al. (2024) to design MICP treatments for specific geotechnical problems, such as bearing capacity [132]. Although the above models well reflect the temporal and spatial evolutions of biochemical substances and permeability in the MICP reaction, it is not applicable to the ocean environment because of the neglect of the ocean dynamic environment factors.

Li developed an MICP reaction model for seabed reinforcement considering the wave actions under the framework of Biot’s consolidation equation [133,134]. According to the existence form of bacteria in the seabed, the total bacteria (C_total) are divided into suspended bacteria (C_bacl) and attached bacteria (C_bacs) on the sand particle surface, assuming that they satisfy the first-order kinetic equation:

$${\displaystyle \frac{\partial C_{bact}}{\partial \mathrm{t}}}=-k_{\mathrm{d}}{C}_{bact}$$

(3)

$${\displaystyle \frac{\partial C_{bacs}}{\partial \mathrm{t}}}=k_{\mathrm{a}\mathrm{t}\mathrm{t}}{C}_{bacl}-k_{\mathrm{d}}{C}_{bacs}$$

(4)

$${\displaystyle \frac{\partial C_{bacl}}{\partial \mathrm{t}}}={-k}_{\mathrm{a}\mathrm{t}\mathrm{t}}{C}_{bacl}-k_{\mathrm{d}}{C}_{bacl}$$

(5)

where k_d is a constant decay rate, and k_att is the constant attachment rate. Urea hydrolysis is described with the adoption of the Michaelis–Menten kinetic equation.

$$k_{\mathrm{r}\mathrm{e}\mathrm{a}}=u_{\mathrm{s}\mathrm{p}}(C_{bacs}+C_{bacl})·{\displaystyle \frac{C_{\mathrm{u}\mathrm{r}\mathrm{e}\mathrm{a}}}{C_{\mathrm{u}\mathrm{r}\mathrm{e}\mathrm{a}}+k_{\mathrm{m}}}}·\exp ((T-25)/{\displaystyle \frac{\ln 3.4}{10}})\exp (-{\displaystyle \frac{t}{t_{\mathrm{d}}}})$$

(6)

where k_m, T, u_sp, C_urea, t, and t_d denote the half-saturation constant at which the reaction rate drops by 50%, environmental temperature, maximum urease activity constant, urea concentration, reaction time, and time constant, respectively.

The hydraulic field is described using Darcy’s law.

$$\mathit{q}=-{\displaystyle \frac{K}{{\mu }_{\mathrm{l}}}}·(\nabla p_{\mathrm{l}}+{\rho }_{\mathrm{l}}\mathit{g})$$

(7)

where q is the Darcy flow rate, K is the matrix permeability, and g stands for gravitational acceleration, while μL, p_l, and ρ_l represent liquid viscosity, excess pore pressure, and liquid density, respectively. All liquid components—including urea, calcium, ammonium, and suspended bacteria—are assumed to be governed by convection–diffusion–reaction equations, as illustrated in Equations (8)–(11).

$$\phi {\displaystyle \frac{\partial C_{\mathrm{u}\mathrm{r}\mathrm{e}\mathrm{a}}}{\partial t}}=\nabla ·\left(\phi {\mathit{D}}^{\mathbf{*}}·\nabla C_{\mathrm{u}\mathrm{r}\mathrm{e}\mathrm{a}}\right)-\mathit{q}·\nabla C_{\mathrm{u}\mathrm{r}\mathrm{e}\mathrm{a}}-\phi k_{\mathrm{r}\mathrm{e}\mathrm{a}}$$

(8)

$$\phi {\displaystyle \frac{\partial C_{{\mathrm{N}\mathrm{H}}_4^{+}}}{\partial t}}=\nabla ·\left(\phi {\mathit{D}}^{\mathbf{*}}·\nabla C_{{\mathrm{N}\mathrm{H}}_4^{+}}\right)-\mathit{q}·C_{{\mathrm{N}\mathrm{H}}_4^{+}}+2\phi k_{\mathrm{r}\mathrm{e}\mathrm{a}}$$

(9)

$$\phi {\displaystyle \frac{\partial C_{{\mathrm{C}\mathrm{a}}^{2+}}}{\partial t}}=\nabla ·\left(\phi {\mathit{D}}^{\mathbf{*}}·\nabla C_{{\mathrm{C}\mathrm{a}}^{2+}}\right)-\mathit{q}·C_{{\mathrm{C}\mathrm{a}}^{2+}}-\phi k_{\mathrm{r}\mathrm{e}\mathrm{a}}$$

(10)

$$\phi {\displaystyle \frac{\partial C_{\mathrm{b}\mathrm{a}\mathrm{c}\mathrm{l}}}{\partial t}}=\nabla ·\left(\phi {\mathit{D}}^{\mathbf{*}}·\nabla C_{\mathrm{b}\mathrm{a}\mathrm{c}\mathrm{l}}\right)-\mathit{q}·C_{\mathrm{b}\mathrm{a}\mathrm{c}\mathrm{l}}-\phi k_{\mathrm{d}}{C}_{\mathrm{b}\mathrm{a}\mathrm{c}\mathrm{l}}-\phi k_{\mathrm{a}\mathrm{t}\mathrm{t}}{C}_{\mathrm{b}\mathrm{a}\mathrm{c}\mathrm{l}}$$

(11)

where C_i denotes the concentration of liquid components, including urea, calcium, ammonium, and suspended bacteria. The variables q and D* (a tensor) represent Darcy velocity and the hydrodynamic dispersion coefficient within the seabed, respectively. The value of D* depends on factors such as pore velocity, dispersivity, pore tortuosity, pore size, and solute concentration gradients. Fick’s law is applied to describe the diffusion of chemical substances from the seabed surface into the seawater, as detailed in Equations (12)–(15).

$${\displaystyle \frac{\partial C_{\mathrm{u}\mathrm{r}\mathrm{e}\mathrm{a}}}{\partial t}}=\nabla ·\left(\mathit{D}·\nabla C_{\mathrm{u}\mathrm{r}\mathrm{e}\mathrm{a}}\right)$$

(12)

$${\displaystyle \frac{\partial C_{{\mathrm{N}\mathrm{H}}_4^{+}}}{\partial t}}=\nabla ·\left(\mathit{D}·\nabla C_{{\mathrm{N}\mathrm{H}}_4^{+}}\right)$$

(13)

$${\displaystyle \frac{\partial C_{{\mathrm{C}\mathrm{a}}^{2+}}}{\partial t}}=\nabla ·\left(\mathit{D}·\nabla C_{{\mathrm{C}\mathrm{a}}^{2+}}\right)$$

(14)

$${\displaystyle \frac{\partial C_{\mathrm{b}\mathrm{a}\mathrm{c}\mathrm{l}}}{\partial t}}=\nabla ·\left(\mathit{D}·\nabla C_{\mathrm{b}\mathrm{a}\mathrm{c}\mathrm{l}}\right)$$

(15)

where D (tensor) represents the hydrodynamic dispersion coefficient in the water phase, and the value of D is always taken as 2 × 10⁻⁹ m²/s. The decrease in the total porosity and the increase in calcium carbonate can be described by

$${\displaystyle \frac{\partial {\phi }_{\mathrm{t}\mathrm{o}\mathrm{t}}}{\partial t}}=-{\displaystyle \frac{1}{{\rho }_{\mathrm{c}}}}{m}_{{\mathrm{C}\mathrm{a}\mathrm{C}\mathrm{O}}_3}{\phi }_{\mathrm{t}\mathrm{o}\mathrm{t}}{k}_{\mathrm{r}\mathrm{e}\mathrm{a}}$$

(16)

$${\displaystyle \frac{\partial C_{{\mathrm{C}\mathrm{a}\mathrm{C}\mathrm{O}}_3}}{\partial t}}=m_{{\mathrm{C}\mathrm{a}\mathrm{C}\mathrm{O}}_3}{\phi }_{\mathrm{t}\mathrm{o}\mathrm{t}}{k}_{\mathrm{r}\mathrm{e}\mathrm{a}}$$

(17)

The Kozeny–Carman (KC) equation is adopted to describe the relationship between porosity and permeability. The concept of the effective porosity and the modified KC equation were adopted in this model [131,135].

$$x={\displaystyle \frac{{\phi }_{\mathrm{t}\mathrm{o}\mathrm{t}}-{\phi }_{\mathrm{c}}}{1-{\phi }_{\mathrm{c}}}}$$

(18)

$${\phi }_{\mathrm{e}\mathrm{f}\mathrm{f}}=a{x}^3-\left(2a+{\phi }_{\mathrm{c}}\right)x^2+\left(a+1+{\phi }_{\mathrm{c}}\right)x$$

(19)

$$k_{\mathrm{i}}=k_0{\displaystyle \frac{{{\left(\right({\phi }_{\mathrm{e}\mathrm{f}\mathrm{f}})}_{\mathrm{i}})}^3}{{(1-{\left({\phi }_{\mathrm{e}\mathrm{f}\mathrm{f}}\right)}_{\mathrm{i}})}^2}}{\displaystyle \frac{{(1-{\left({\phi }_{\mathrm{e}\mathrm{f}\mathrm{f}}\right)}_0)}^2}{{{\left(\right({\phi }_{\mathrm{e}\mathrm{f}\mathrm{f}})}_0)}^3}}$$

(20)

where i represents the current time step, k_i and k₀ are the current permeability and initial permeability, and (φ_eff)_i and (φ_eff)₀ represent the current effective porosity and initial effective porosity.

For the homogeneous and isotropic seabed, the theoretical equations are as follows [17]

$$G{\displaystyle \frac{2-2\nu }{1-2\nu }}{\displaystyle \frac{{\partial }^{2}u}{\partial z^2}}={\displaystyle \frac{\partial p}{\partial z}}$$

(21)

$${\displaystyle \frac{k}{{\gamma }_{\mathrm{w}}}}{\displaystyle \frac{{\partial }^{2}p}{\partial z^2}}={\displaystyle \frac{{\partial }^{2}u}{\partial z\partial t}}+\phi \beta {\displaystyle \frac{\partial p}{\partial t}}$$

(22)

where G denotes the shear modulus of the seabed, which increases as the calcium carbonate content rises. The vertical coordinate z originates at the seabed surface, with positive direction pointing downward. Here, u represents soil displacement, υ is Poisson’s ratio, and p is excess pore pressure. The parameters k, γ_w, φ, and β correspond to the permeability coefficient, water unit weight, seabed porosity, and effective compressibility of the combined liquid–gas phase, respectively.

$$\beta =({\displaystyle \frac{1}{K_{\mathrm{f}}}}+{\displaystyle \frac{1-S_{\mathrm{r}}}{p_{\mathrm{w}0}}})$$

(23)

where S_r is the saturation degree of the seabed, p_w0 is the absolute static pressure, and K_f is the bulk modulus of the pore water. The pore pressure p affects the Darcy velocity, thus affecting the convection–diffusion–reaction process and the precipitation of calcium carbonate. Conversely, the CaCO₃ 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.

Li 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–t₁); (2) injection of cementing solution (t₁–t₂); (3) MICP reaction phase (t₂–t₄), where urea and calcium are consumed and calcium carbonate precipitates, leading to increased strength and reduced porosity; and (4) wave impact phases—during (t₃–t₄) and after (t₄–t₅) 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.

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_c is ignored, the MICP-treated seabed started to be unstable when the wave height reached 2 m. When the inner cohesive force F_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.

4. Suggestions for Future Research

Although MICP technology has been applied to control erosion and liquefaction in ocean engineering, from units, models, to a small number of fields, there are still issues that should be considered, such as low reinforcement efficiency, insufficient reinforcement durability, and possible foreign microbial invasion concerns. In addition, current experimental studies have basically ignored the mutual coupling effects of MICP reaction and common ocean dynamic environmental elements such as waves and currents. To ensure the responsible and sustainable application of MICP in marine environments, future research should prioritize practical and urgent needs. In the short term, efforts should focus on conducting life cycle assessments (LCAs) to evaluate the overall environmental footprint, assessing potential ecosystem impacts to avoid unintended consequences, and performing durability testing to ensure long-term performance under harsh marine conditions. Screening and utilizing indigenous urease-producing bacteria is essential to reduce ecological risks associated with non-native microbial introduction. Additionally, developing ecological monitoring strategies—such as environmental DNA (eDNA) tracking, microbial community analysis, and water quality monitoring (e.g., ammonia, pH)—will help track changes in the environment during and after MICP application. Multi-scale experiments (e.g., in tidal tanks) can simulate real ocean conditions, while the integration of real-time sensors can enable in situ monitoring and adaptive control of treatment processes. In the long term, advanced approaches such as gene editing may be used to enhance microbial performance in a controlled and safe manner, while AI-based optimization could help tailor treatment plans to site-specific conditions. Furthermore, addressing practical challenges in large-scale deployment—including injection logistics, treatment scalability, and meeting regulatory standards—is crucial for successful field application. This balanced and forward-looking approach aims to bridge scientific innovation with environmental responsibility and real-world engineering needs.

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 CaCO₃ precipitation by >2 h and acts as a non-bacterial nucleation template, facilitating spatially uniform distribution. Kinetic analysis of Ca²⁺ 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% CaCO₃ 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 CaCO₃ (9.9%) near gravel interfaces, collectively enabling the slope to withstand Hurricane Dorian over 331 days. Meanwhile, Sanya’s studies highlighted seawater-compatible MICP solutions, achieving maximum 1743 kPa penetration resistance in the atmospheric zone and layered “M-shaped” CaCO₃ 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 CaCO₃-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. Surface CaCO₃ clogging diminishes permeability and redistributes seepage forces, enhancing resistance to liquefaction. Comparative analyses confirm untreated seabed instability increases linearly with wave height, while MICP-treated seabed exhibits nonlinear stability gains through cohesive strength effects. Validated via unit tests and parametric studies, the model demonstrates MICP’s efficacy in mitigating wave-induced seabed liquefaction.

While MICP shows great potential for reducing erosion and liquefaction in coastal and seabed environments, key challenges remain in improving treatment efficiency, durability, and minimizing ecological risks from non-native microbes. Future research should prioritize the following: (1) developing indigenous urease-producing bacteria and carefully evaluating ecological impacts; (2) conducting multiscale studies on the interaction between hydrodynamics and MICP processes to understand mass transfer and long-term stability under dynamic ocean conditions; (3) performing comprehensive field validations to measure protection effectiveness and biomineralization persistence in tidal and wave-affected zones. Additionally, interdisciplinary collaboration among microbiologists, ocean engineers, and environmental scientists is essential to address these complex challenges. Tackling these priorities will advance eco-friendly, effective MICP solutions for sustainable marine engineering.