Advances in MICP reinforcement technology used in island engineering

Being an environmentally friendly technology, Microbially Induced Calcium Carbonate Precipitation (MICP) has become a popular research topic in the field of geotechnical and environmental engineering, among which island microbial technology is a promising direction. This paper systematically summarizes the basic principles of microbial mineralization and the progress made in the use of MICP in construction work done on islands, such as the reinforcement of calcareous sand, protection of island slopes from erosion, and reinforcement of pile foundations, and the numerical modeling performed in island engineering. The following conclusions can be drawn: MICP produces calcium carbonate, which is the same as calcareous sand, and thus MICP can be used to meet the ecological reinforcement requirements of islands. The temperature and soil pH of the islands are suitable for MICP. Urease activity in soil nonlinearly increases as environmental temperature increases in the range from 5 ℃ to 40 ℃, and the soil pH influences pore solution concentrations, which in turn affects the deposition rate, yield, and morphology of calcium carbonate. The optimal pH value required for the mineralization caused by Sporosarcina pasteurii is approximately 9. However, the influence of the special environmental characteristics of islands, such as radiation, waves and currents, on MICP requires further study. Island microbial technology can be used to greatly enhance the strength and stiffness of calcareous sand in islands, the bearing capacity of pile foundations constructed in islands, and the erosion resistance of island slopes against waves and currents. The verification of the applicability of MICP in an island environment and the determination of the efficiency of bacterial urease activity, morphology and deposition rate of calcium carbonate in calcareous sand, physical and mechanical properties and uniformity of cemented calcareous sand layers in that environment require in-situ reinforcement tests. Most of the previous research on MICP is laboratory experiments. The spatiotemporal evolutions of the chemical substances used in various processes of MICP cannot be determined in real-time. The labor and other resources used in field experiments, which are highly dependent on field conditions, are expensive. Therefore, a reliable numerical model is highly important to understand the biochemical processes associated with MICP. However, research on MICP numerical models is still in its infancy, and currently, the MICP models are verified mainly using element and model tests. The development of a numerical model for the multiple processes of MICP suitable for the environmental conditions, such as temperature, soil pH, waves, and currents, of an island and verification of the accuracy of the model based on in situ reinforcement tests is extremely important. The findings can provide a reference for soil reinforcement in an island environment using MICP.