Use of nebulisers to deliver cementation liquid in granular soils to form biogrout

The use of urease enzyme to deposit calcium carbonate (CaCO₃) for ground treatment of granular soils has typically relied on injection or percolation of liquid solutions. This approach can result in an uneven distribution of biogrout and loss of cementation liquid from percolation through the ground into the underlying groundwater system. As an alternative approach, laboratory experiments have demonstrated the potential of using aerosols to deliver fine micro droplets of reagent liquids into the unsaturated zone to promote calcium carbonate deposition at soil–particle interfaces. Scanning electron microscopy images taken of soil samples showed markedly different crystal morphology and particle bond formations for liquid percolation compared with aerosol injection methods. In particular, the bond formation created from aerosol droplets was found to replicate the curved surface of liquid menisci between soil particles, leading to a dual-bond meniscus structure. The resulting unconfined compressive strengths were comparable with similar increases in strength created from percolation and liquid-flushing methods. The results show the potential to use aerosol liquid delivery to promote ground improvement in the vadose zone for granular soils, where possible collapse of residual soils could be addressed, or to strengthen granular soils to resist additional forces such as earthquake loading.