Biological processes may provide great and previously unexplored opportunities for in situ, cost effective soil improvement. A laboratory research study was conducted to evaluate the changes in geomechanical properties of sand due to microbial precipitation of calcium with Bacillus pasteurii. Direct shear tests and California bearing ratio (CBR) were conducted on the soils subjected to microbial calcite precipitation in the completely stirred tank reactors and completely mixed biofilm reactors, respectively. Scanning electron microscopy (SEM) analyses were conducted to evaluate the performance of microbial precipitation.

Results of the study show that: (1) the bioinduced calcites effectively improve geomechanical properties of sand, (2) live cells significantly improve the properties due to biotic conditions and related pore volume changes, while both dead and resting cells act like organic fibers and cause lower but notable increases in friction angle and bearing strength, and (3) bio-plugging of the column is mostly due to calcite formation, and not biomass accumulation, as evidenced in SEM analyses.