A PRISMA-guided systematic review of MICP and EICP in clayey soils: Mineralogy-aware mechanisms, injection control, and multi-scale performance synthesis

• This PRISMA-based SLR synthesizes 37 studies (2020–2025) on MICP/EICP in clayey and low-permeability soils. • Mineralogy-controlled mechanisms are mapped against CaCO₃ morphology, injection strategies, and mechanical–hydraulic outcomes. • Comparative performance analysis distinguishes the effects of curing duration, urea–Ca²⁺ balance, mineral type, and nano-additives. • A unified framework linking injection control, soil mineralogy, and microstructural evolution is developed for field-scalable design. • Key research gaps and implementation pathways are proposed for engineering practice and field deployment. This study conducts a PRISMA-guided systematic review of Microbially Induced Calcite Precipitation (MICP) and Enzyme-Induced Calcite Precipitation (EICP) for improving the mechanical and hydraulic performance of clayey soils. The review synthesizes 37 peer-reviewed studies published between 2020 and 2025, evaluating relationships among microbial activity, chemical parameters, injection techniques, and soil mineralogy. Findings indicate that MICP generally yields higher unconfined compressive strength and lower permeability than EICP due to more efficient bacterial nucleation and calcite bonding. Controlled injection and electro-osmotic delivery enhance calcium carbonate uniformity, while extended curing promotes crystal densification and strength development. The addition of nano-SiO₂ and hybrid lime–MICP systems further refines microstructure and increases durability. Microstructural analyses using SEM, EDS, and XRD confirm rhombohedral calcite formation bridging clay particles, linking microscopic bonding with macroscopic strength gains. Key influencing factors include urea–Ca²⁺ balance, curing duration, and clay mineralogy. Identified limitations involve non-uniform precipitation, bacterial inactivity, and salinity inhibition, which can be mitigated through staged feeding, optimized ionic strength, and adaptive field protocols. Integrating sustainability assessment through Multi-Criteria Decision Analysis (MCDA) provides a framework for balancing performance, environmental impact, and cost efficiency. Overall, this review establishes mineralogy-aware and process-controlled bio-cementation as a scalable, sustainable alternative to traditional soil stabilization for fine-grained and low-permeability soils.