Geotechnical Insights into the Experimental Use of Proteus mirabilis for Calcite Precipitation of Lateritic Clay Soils

The uptake and use of microbial–induced calcite precipitation (MICP) for soil improvement has significantly increased since its application was discovered two decades ago. Most research and fieldwork focus more on its application in sandy soil improvement because soils with smaller pore sizes inhibit the movement of bacteria. The effects of Proteus mirabilis on the geotechnical properties of a lateritic clay was investigated. The index properties, compaction characteristics, strength characteristics, and chemical and morphological properties of the lateritic clay were determined. The soil is classified as a sandy clay (CL) based on the Unified Soil Classification System (USCS) and as an A–7–6 soil based on the American Association of State Highway and Transportation Officials (AASHTO) classification system. The soil was then treated with 0, 1.5×108 , 6.0×108 , 1.2×109 , 1.8×109 , and 2.4×109 cells/ml Proteus mirabilis suspension density. Comparing maximum dry density (MDD) and unconfined compressive strength (UCS) of the natural soil and soil treated with 2.4 x 109 cells/ml bacteria suspension, the MDD of the natural soil increased from 1648 kg/m3 to 1768 kg/m3 while the UCS of the soil increased from 129.09 kN/m2 to 172.7 kN/m2 , respectively. Micrographs of the treated soils showed a reduction in pore spaces due to the precipitation of calcites in the pores. With a 33.8% increase in the UCS of the natural soil due to calcite precipitation, this study shows the prospect of using Proteus mirabilis as an environment–friendly means of improving the geotechnical strength of soils.