Engineering Properties of Bio-Cementation Improved Sandy Soils

Microbially induced calcite precipitation (MICP) is an environmentally conscious soil improvement technique that can improve the geotechnical properties of granular soils through the precipitation of calcite on soil particle surfaces and at particle contacts. In this study, synthesis of results from 47 soil column experiments involving 14 different soil materials was completed to provide a preliminary characterization of the range of engineering properties obtainable with MICP ground improvement. Following treatment, soil column specimens had unconfined compressive strengths ranging from 0.22 to 5.34 MPa, shear wave velocities ranging from 151 to 1469 m/s, and hydraulic conductivity reductions ranging from 0 to 3.5 orders of magnitude. Relationships between post-treatment soil improvement, soil properties, and calcite content suggest that D₁₀ particle size and fines content may significantly influence unconfined compressive strength and hydraulic conductivity, however, shear wave velocity may be less sensitive to these material differences. In addition, a comparison of final calcite contents between experiments suggests that soil fines contents up to 13% may not significantly affect calcite precipitation efficiency. An overview of the MICP reaction, biological treatment approaches, and process monitoring methods are also provided to introduce the bio-mediated soil improvement technology.