Bio-stabilisation of dispersive soils

Dispersive soils are among problematic soils encountered in many parts of the world. In these soils, the soil particles disperse into solution upon saturation and thereby increase the piping potential of these soils. Therefore, stabilisation of these soils is of great concern for geotechnical engineers. Soil chemistry can affect dispersivity of the soil and high sodium content can bring about dispersivity of the soils. Therefore, these soils are also called sodic soils. To decrease soil dispersivity, there are different remedial measures among which biological stabilisation is a novel method which has been investigated in this research. In the current study, biological stabilisation of dispersive soils by means of microbial calcite precipitation and its controlling factors affecting the stabilisation have been explored. The bacterium Bacillus sphaericus has been used. Pinhole tests are used to investigate dispersivity of synthetic dispersive soil samples. Soil samples before and after biological stabilisation have been carefully tested to determine their level of dispersivity. The target variables are the curing time with bacterial cell density while other influencing factors such as soil moisture content and nutrient content are kept constant. The test results demonstrated that microbial calcite precipitation is a promising technique for stabilising dispersive soils. The dispersivity of the treated samples decreases as the curing time and bacterial cell density of the treated samples increases.