Microbial Carbonate Precipitation as a Soil Improvement Technique

Abstract

In order to evaluate MCP as a soil strengthening process, a five meter sand column was treated with bacteria and reagents under conditions that were realistic for field applications. The injection and reaction parameters were monitored during the process and both bacteria and process reagents could be injected over the full column length at low pressures (hydraulic gradient < 1; a flow rate of approximately 7 m/day) without resulting in clogging of the material. After treatment, the column was subjected to mechanical testing, which indicated a significant improvement of strength and stiffness over several meters. Calcium carbonate was precipitated over the entire five meter treatment length. Improvement of the load bearing capacity of the soil without making the soil impermeable to fluids was shown with microbial carbonate precipitation, and this is a unique property compared to alternative soil treatment methods that are currently available for use in the subsurface.

Keywords:

• Microbial carbonate precipitation
• soil improvement
• strengthening
• urease

Acknowledgments

With regard to the specific work in this study, the authors would like to acknowledge the expert technical assistance of Mr Ferry Schenkeveld, Mr Willem van Pernis and Dr Jacco Booster, all of GeoDelft. This work is part of a larger research project funded by Senter Novem in conjunction with GeoDelft, VWS Geotechniek and Delft University of Technology. In addition we would like to acknowledge Dr. Ralf Cord-Ruwisch and Ms. Salwa Al-Thawdi (Murdoch University), and Dr. Edward Kucharski (Calcite Technology Pty Ltd.) for their prior contribution in the initial process development.