Microbial Carbonate Precipitation as a Soil Improvement Technique

TLDR

The study evaluated microbial carbonate precipitation (MCP) as a soil strengthening technique by treating a five‑meter sand column with bacteria and reagents under field‑like conditions. Bacteria and reagents were injected along the entire column at low hydraulic gradients (<1) and flow rates (~7 m/day), with injection and reaction parameters monitored to avoid clogging. MCP precipitated calcium carbonate throughout the column, significantly increasing strength, stiffness, and load‑bearing capacity while preserving permeability—an advantage over existing subsurface soil treatments.

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.