Bio-Grout Based Soil Improvement-Paper

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The paper presents bio-grouting as a lower-impact alternative to conventional cementitious and chemical ground treatments. It uses enzymes or microorganisms to convert urea into carbonate, which combines with calcium to form calcite. The crystals grow at soil-grain contacts, creating mineral bridges that increase strength and stiffness without completely filling the soil’s pores; permeability is generally retained, allowing drainage and possible reinjection.<br /><br />Bio-grout behaves much like water during injection, so it can penetrate fine fissures and be applied at low pressures using equipment similar to conventional cement grouting. It is suitable for a range of soils, from silts to gravels, and can be used in saturated or unsaturated conditions. A key environmental challenge is nitrogen produced during the reaction. The system described addresses this through an external ammonia-capture and recycling process, leaving treated soil rich in carbonate and with reduced nitrogen residues.<br /><br />The paper outlines the materials, injection procedures, and quality-control methods, including calcite-content testing, geotechnical tests, and geophysical surveys. Typical reported improvements include greater cohesion, friction angle, stiffness, unconfined compressive strength, and shear-wave velocity, though outcomes depend on site conditions and treatment design.<br /><br />A Swiss case study applied bio-grout to stabilize weathered, weakly cemented sandstone beside a road. About 1.3 tonnes of reactive liquid were injected through seven boreholes in four cycles, at pressures of 0.3–0.5 bar. Seismic tomography showed post-treatment P-wave velocities of up to 2,500–3,000 m/s, with increases of up to 90% in some areas, indicating substantial cementation.<br /><br />The authors conclude that bio-grouting has potential for minimally invasive, rapid, and cost-effective soil improvement, while retaining drainage capacity and supporting the reuse of treatment inputs.

Keywords

bio-grouting

calcite

urea hydrolysis

soil stabilization

ground improvement

microbial induced calcite precipitation

permeability

ammonia recycling

seismic tomography

Swiss case study