Effect of microbial-induced calcite precipitation on hydraulic conductivity and strength of a sandy gypseous soil

This work presents the effect of microbial induced calcite precipitation treatment on hydraulic conductivity and strength of a sandy gypseous soil with about 35% gypsum content. The cementitious material was produced from a bacterial suspension containing the bacterial strain Bacillus Pasteurii PTCC 1645, mixed with or added to a cementation solution having the molarities 0.25, 0.5, and 1 M and prepared from a number of typically used chemical substances. The work resulted in a number of important outcomes. The microbial-induced calcite precipitation (MICP treatment), which yielded about 15% calcite carbonate after 14 to 21 days of curing, can efficiently reduce the hydraulic conductivity, even for soils with high gypsum contents and relatively low fine content. In response to curing time increase from 7 to 21 days, the hydraulic conductivity decreased nearly twice. Likewise, as the calcite content increased to 15%, the hydraulic conductivity decreased by almost fourfold. On the compressive strength front, the MICP treated specimens showed a promising uniaxial compressive strength of up to 600 kPa. This further reinforces the perception that MICP treatment by the Bacillus Pasteurii strain can be used effectively in treating gypseous soils problems.