Soil improvement is one of the most important issues in geotechnical engineering practice. The wide application of traditional improvement techniques (cement/chemical materials) are limited due to damage ecological environment and intensify carbon emissions. However, the use of microbially induced calcium carbonate precipitation (MICP) to obtain bio-cement is a novel technique with the potential to induce soil stability, providing a low-carbon, environment-friendly, and sustainable integrated solution for some geotechnical engineering problems in the environment. This paper presents a comprehensive review of the latest progress in soil improvement based on the MICP strategy. It systematically summarizes and overviews the mineralization mechanism, influencing factors, improved methods, engineering characteristics, and current field application status of the MICP. Additionally, it also explores the limitations and correspondingly proposes prospective applications via the MICP approach for soil improvement. This review indicates that the utilization of different environmental calcium-based wastes in MICP and combination of materials and MICP are conducive to meeting engineering and market demand. Furthermore, we recommend and encourage global collaborative study and practice with a view to commercializing MICP technique in the future. The current review purports to provide insights for engineers and interdisciplinary researchers, and guidance for future engineering applications.

Massive dredged sludge is being landfilled without effective use due to its high-water content and poor engineering properties, which not only leads to soil resources waste, but also occupies a large amounts of land sources. In this study, ternary stabilizer, including waste phosphogypsum (PG), ground granulated blast-furnace slag (GGBS), and lime (LM) with a mixing proportion of PG: GGBS: LM = 35:60:5, was adopted to improve the mechanical and environmental behaviors of sludge for subgrade filling purpose. The initial water content of sludge was controlled using two different dehydration methods for comparison. A series of laboratory tests, including unconfined compressive strength (UCS), organic matter content, and pH value were tested to understand its physical-mechanical properties. Thereafter, field application model equipped with a mini weather monitoring station was constructed to monitor the influence of solidified matrix on the surrounding water and soil environment. Time -dependent parameters such as plant growth, temperature, humidity, total nitrogen, phosphorus/potassium content, electrical conductivity, and pH value were monitored. Results indicate that the incorporation of PG-GGBS-LM ternary stabilizer significantly improves the mechanical and environmental properties of dredged sludge. The optimal dosage of the ternary stabilizer is 36%, which can result in a UCS value of the 2.0 MPa (slightly higher than ordinary Portland cement) after 28 days of curing. Field application reveals that plants could grow normally in solidified sludge. The environmental related parameters (i.e., total nitrogen, phosphorus/potassium content, electrical conductivity, and pH value) were similar with those in conventional planting soil, suggesting the advantage of the proposed PG-GGBS-LM ternary stabilizer in mechanical, economic and environmental aspects.