Stabilization of expansive black cotton soil using bioenzymes produced by ureolytic bacteria

AbstractSoil stabilization is the art and science of improving the engineering properties of soils. The properties of problematic soils can be improved by blending appropriate amount ofinsitusoil, aggregates and bioenzymes. In the present study, four bacterial strains:Sporosarcina pasteurii, Bacillus paramycoides, Citrobacter sedlakii,andEnterobacter bugadensiswere used to produce bioenzymes using urea supplemented molasses as a substrate via submerged fermentation. The crude bioenzyme was mixed with modified soil blended with 40% black cotton soil, 30% aggregate and 30% river sand; then tested after curing for 7 days. The test results revealed that except soil samples treated with bioenzyme ofEnterobacter bugadensis, all treated soil samples showed improved plasticity index (18–55%) and liquid limit (5–44%). Soil samples treated with bioenzyme ofBacillus paramycoides,Citrobacter sedlakiiandSporosarcina pasteuriishowed higher CBR values of 12.9%, 12.27%, and 11.95% respectively. On the other hand, free swell showed reduction in soil samples treated with bioenzymes ofSporosarcina pasteurii(47.37%),Bacillus paramycoides(30%), andCitrobacter sedlakii(10.53%). The highest percentage improvement of linear shrinkage was recorded for soil sample treated with bioenzymes ofSporosarcina pasteuri(39.65%), followed by Permazyme (10.44%),Citrobacter sedlakii(8.4%) andBacillus paramycoides(8.34%). Whereas, the highest percentage improvement in MDD was recorded in permazyme treated soil (11.92%) followed by molasses (8.29%),Bacillus paramycoides(1.92%), andEnterobacter bugadensis(0.73%). The lowest optimum moisture content (9.3%) was recorded in soil treated with permazyme. Triaxial test analysis also showed improvement in both cohesion and angle of friction in bioenzyme treated soils. From the test results it was concluded that it is possible to treat expansive black cotton soils using bioenzymes produced from low cost substrates such as molasses and reduce the cost of construction and environmental carbon emission.