Enzyme-Induced Carbonate Precipitation: Scale-Up of Bio-Cemented Soil Columns

A 0.3 m-diameter×0.9 m-long bio-cemented soil column was created in a 0.6 m×0.6 m×1.2 m box filled with dry quarry sand using enzyme induced carbonate precipitation (EICP). The bio-cemented column was created using controlled rate injection through a tube-a-manchette pipe. The EICP solution had concentrations of 1.5 M urea, 1 M calcium chloride, 9,900 U/l urease enzyme, and 4 g/l of nonfat milk powder. Three treatment cycles were applied. After three days, the bio-cemented column was exposed. The column was measured to be within 10% of the design diameter, but was 20% longer. As the column was deconstructed, needle penetrometer tests performed on various layers indicated that the design unconfined compressive strength of 500 kPa was achieved. While UCS tests on specimens sub-sampled from the column had an average strength of 154 kPa, the specimens appeared to have been disturbed during the sub-sampling process as they exhibited local failure at the ends or outer surface. Overall, these results demonstrate that EICP has potential as a ground improvement method because it can be designed and implemented in the field to strengthen soil using installation methods similar to conventional permeation grouting techniques. Potential applications at greenfield sites or underneath existing structures/infrastructure include bearing capacity improvement, settlement mitigation in loose sands, and prevention of running sands during excavations and tunneling.