# Recent Developments on Biomineralization for Erosion Control
## 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 km\({}^{2}\) per year [1]. Approximately 86% of East Coast beaches in the United States have undergone erosion during the last100 years [2]. Between 1984 and 2015, erosion claimed 28,000 km\({}^{2}\) 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 km\({}^{2}\) 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 [PERSON] and [PERSON] (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]. 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 nonurishment, and mangrove afforestation [27; 28; 29; 30; 31; 32; 33; 34; 35].