Mechanical behavior and precipitation characteristics of EICP–treated sand: role of particle size and relative density

Enzyme–induced carbonate precipitation (EICP) is a highly promising and environmentally friendly soil stabilization technique, whose treatment effectiveness is largely governed by soil particle size and initial density state. Accordingly, Fujian standard sands with different relative densities ( D r ) and mean particle sizes ( d a ) were treated using a single–phase low–temperature vacuum grouting (SPLTVG) method. The resulting EICP–treated specimens were subjected to uniformity evaluation and unconfined compressive strength (UCS) tests to systematically investigate the effects of D r and d a on EICP treatment performance. The results indicate that EICP treatment is more effective in sands with higher D r and smaller d a . Such specimens exhibit higher average calcium carbonate density ( ρ c,a ) and greater peak unconfined compressive strength ( q ua ) after treatment, where ρ c,a represents the amount of calcium carbonate precipitated per unit volume of soil. Meanwhile, increasing D r and decreasing d a enhance the secant modulus ( E 50 ) while reducing the failure strain ( ε f ), leading to a more brittle failure behavior. Based on the quantified effects of D r and d a on q ua and E 50 , together with the underlying mechanisms revealed by microstructural analyses, the concept of effective calcium carbonate density ( ρ c,e ) is proposed, which characterizes the fraction of calcium carbonate precipitated in the cementation mode. This parameter is further employed to normalize the influences of D r and d a on the relationships between q ua and ρ c,a , as well as between E 50 and ρ c,a . Finally, predictive models for q ua and E 50 of EICP–treated soils are established in terms of ρ c,e , in an effort to facilitate the application of EICP technology in practical foundation and subgrade engineering.