Biocalcification of Sand through Ureolysis

Biological processes may provide great and previously unexplored opportunities for cost-effective, in situ improvement of the engineering properties of soil. A laboratory study was conducted to evaluate the changes in geomechanical properties of sand attributable to the formation of calcium precipitates induced through ureolysis catalyzed by Sporosarcina pasteurii (S. pasteurii). Specifically, direct shear and California Bearing Ratio (CBR) tests were conducted on sand specimens subjected to treatment by growing, resting, and dead S. pasteurii cells in completely stirred tank reactors and completely mixed biofilm reactors, respectively. Scanning electron microscopy analyses were also conducted to evaluate microbially induced precipitation. The results of the study show that the bacterial cells effectively improved the geomechanical properties of the sand. Growing cells improved the sand properties owing to microbially induced precipitation and related pore volume changes, whereas dead and resting cells generally caused smaller increases in friction angle and bearing strength. Analysis of the sand from CBR specimens treated with growing cells demonstrated that the microbial and chemical processes both contributed to the clogging of the porous medium.