Minimally Invasive Approach for Efficient Soil Treatment Based On Bio-Grout-Paper

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The paper presents bio-grouting, a minimally invasive method for strengthening soils and weak rock through calcium carbonate (calcite) formation. Enzymes or microorganisms catalyze the conversion of urea into carbonate, which reacts with calcium in solution. Calcite crystals grow on soil grains and form mineral bridges, increasing strength and stiffness without filling all the pores; soil permeability is therefore largely retained, allowing drainage and possible reinjection.<br /><br />Bio-grouts have water-like flow properties and can penetrate very small openings. They are injected using conventional grouting equipment at low pressures, reducing vibration and risks to nearby structures. The method can treat soils from silts to gravels, and can be adapted to finer soils using electro-osmosis. The paper also describes an ammonia-capture and recycling system that separates nitrogen from the carbonate solution, aiming to limit residual byproducts and support reuse of materials.<br /><br />A Swiss case study used bio-grouting to stabilize weathered, weakly cemented sandstone beside a road. Approximately 1.3 tonnes of reactive solution were injected through seven boreholes over four cycles, at pressures of 0.3–0.5 bar. Seismic tomography showed substantial increases in P-wave velocity, reaching 2,500–3,000 m/s in treated areas. Electrical resistivity monitoring and ground-penetrating radar also indicated fluid penetration and post-treatment changes consistent with consolidation.<br /><br />The authors report that bio-grouting can provide rapid, cost-effective ground improvement while retaining drainage capacity and reducing environmental impacts compared with conventional cementitious or chemical grouts. Its practical application, they argue, has advanced through improved process control, monitoring, and management of nitrogen byproducts.

Keywords

bio-grouting

soil stabilization

calcite formation

microbial grouting

calcium carbonate

ground improvement

permeability retention

low-pressure injection

seismic tomography

ammonia recycling