A new biogrouting method for fine to coarse sand

Permeation grouting using cement is widely used for ground improvement. However, this method can only be used for coarse sand or gravel. To overcome this problem, permeation grouting using biogrout through a microbially induced calcium carbonate precipitation method has also been developed. Biogrout is finer and thus can permeate through fine sand. However, biogrouting method is not efficient for medium or coarse sand. For this reason, different grouting methods or materials may have to be used when the ground conditions are highly variable. It will be more efficient and highly desirable to apply only one grouting method to ground with soils of different grain sizes. In this study, a new biogrouting method using biogrout containing bioslurry is developed to allow soil with grain sizes ranging from fine to coarse sand to be treated efficiently. Bioslurry is a slurry containing preformed urease active calcium carbonate crystals, and biogrout is made of mainly calcium ions, urea and urease-producing bacteria. The testing results on sands with grain sizes ranging from 0.30 to 2.36 mm have shown that the proposed method could be applied to sand of different sizes by varying the solid content in the bioslurry. For medium or coarse sand, biogrout with a high solid content (i.e., 20–40%) can be used, whereas for fine sand, biogrout with a low or zero solid content will work. Furthermore, the effect of grain size, the type of biogrout, and CaCO3 content on permeability and uniaxial compression strength of grouted sand were also investigated.