Optimisation of microbially induced calcite precipitation protocol against erosion

Five strategies of microbially induced calcite precipitation (MICP) are suggested to improve the uniformity of treatment and enhance the erosional/hydraulic response of internally unstable and poorly graded soils. The treatment consisted of the injection of a bacterial suspension and a cementation solution. The volume of the injected bacterial suspension varied from 0·3 to one pore volume, while the concentration of the cementation solution (urea/calcium chloride (CaCl₂)) varied from 0·35 to 0·75 M. The biotreatment of sand columns (φ = 160 mm and h = 100 mm) was conducted in either one, two or three stages, with or without a low-salinity fixation solution. The biotreated specimens were then submitted to an erosion test, and the results show that alternating injection of reagents in three stages enhances the uniformity of biomineralisation, as the hydraulic conductivity is constant from the top to the bottom of the specimens. This protocol also prevents internal erosion as the critical hydraulic gradient (i _cr) is equal to 10 and the cumulative fine loss (M _e) does not exceed 63 g/m². Finally, the use of a fixation solution prevents any clogging near the injection point and stimulates the bacterial transport in the soil.