Investigation of biostimulation feasibility in dumped soils of lignite opencast mines

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4. Investigation of biostimulation feasibility in dumped soils of lignite opencast mines

Microbially Induced Calcite Precipitation (MICP) has emerged as a promising method to improve the engineering characteristics of different soil types in recent years. Biostimulation, a novel approach within this field, accelerates the urea hydrolysis process through the enrichment of native ureolytic bacteria in the soil, facilitating calcite precipitation in the presence of a calcium source. In the present study, the potential of MICP through biostimulation has been investigated for the improvement of dumped granular soils in the lignite opencast mines of the Rhenish mining area in Germany. After depletion these mines will be recultivated as lakes, with the loose to medium dense dumped soils forming the embankments. MICP could be used if stabilization of embankments is necessary, in particular with respect to the seismic loading to be expected in that region. The presence of native ureolytic bacteria in sandy soils collected from the dump sites of the Rhenish lignite mining area was examined by suspending the soils in enrichment media. Additionally, the improvement of the engineering properties of the dumped soils was investigated through the biostimulation of soil specimens in 100 mL sterile syringes. Subsequently, mechanical element tests on the unconfined compressive strength (UCS) and permeability were performed on the samples. Furthermore, calcite content measurement and SEM imaging were conducted to determine the calcite precipitation pattern within the volume of the samples. The pH increase and urea concentration decrease observed in both batch experiments and element tests confirmed the presence of native ureolytic bacteria in the dumped soils. Moreover, the MICP-treated sand samples reached UCS values of about 300 kPa and a permeability decrease of about two orders of magnitude following the treatment process. These results demonstrate the feasibility of the biostimulation approach for the improvement of the collected granular soils from the dumps of the Rhenish lignite mining area.

2025 International Conference on Bio-mediated and Bio-inspired Geotechnics (ICBBG2025)

General session: Case studies on field application of biogeotechnics