Scale up of BioGrout: A biological ground reinforcement method

BioGrout is a new soil improvement method based on microbiologically induced precipitation of calcium carbonate. Bacteria, which are able to convert urea into ammonium and carbonate, are injected in the soil, followed by a solution containing urea and calcium chloride. The produced carbonate precipitates with calcium. The calcium carbonate crystals form bridges between the sand grains, which increases the strength of the sand mass. The remaining ammonium chloride is extracted. In the laboratory, we proved the prospect of BioGrout as soil improvement method with sand column experiments. The next challenge was to establish homogeneous strengthening over larger soil volumes. We evaluated the new technology in a step-wise scale-up approach. First, biogrouting was applied in sand filled boxes of 1 cubic meter, simulating a single point injection. Recently, we used a large scale sand box (100 m ³) in which the sand was treated over a distance of 5 m using screens of injection and extraction wells. The tests showed that it was possible to turn sand biologically into sandstone (UCS up to 12 MPa) using conditions and techniques as encountered in practice. Special attention is paid to the distribution of the calcium carbonate content and geomechanical parameters within the grouted sand bodies.