Bio-stabilisation of soils using crude urease enzymes: mechanisms, applications and challenges

The shift towards sustainable, low-carbon ground improvement has positioned enzyme-induced carbonate precipitation (EICP) as a promising bio-mediated soil stabilisation technique. Crude plant-derived urease, especially from jack bean and soybean, has shown potential in enhancing soil strength and reducing permeability through calcium carbonate precipitation within pore spaces. Compared with microbial-induced carbonate precipitation (MICP), EICP avoids biosafety concerns and bacterial viability constraints and exhibits improved transport potential in fine-grained soils. The reported strength, however, from crude urease-based EICP generally remains within the sub-megapascal to low-megapascal range and is comparable to, but not exceeding, those achieved by optimised MICP treatments under laboratory conditions. The performance of EICP shows substantial variability across soil types and treatment procedures, and current evidence is dominated by small-scale laboratory studies. This review focuses on EICP using crude urease extracts, examining enzyme extraction methods, treatment strategies, and the influence of various additives. Laboratory-based durability assessments, including wet-dry and freeze-thaw cycles, are critically discussed, while emphasising the absence of long-term field monitoring data. Key constraints related to pore-scale transport, environmental sensitivity, ammonium by-products and scalability are addressed. Also, several research gaps are identified to guide future mechanistic modelling, controlled field trials and the development of hybrid stabilisation approaches.