Biocementation of an Organic Soil with Electrokinetics

This thesis assesses the feasibility of biocementation of a problematic organic foundation soil of many embankments of the East Anglia railway network. Biocementation has recently attracted the interest of the researchers worldwide as an emerging soil stabilisation technique, proposed as environmentally friendlier and more sustainable than other soil stabilisation techniques; however, evidence of its effectiveness as a stabilisation technique for soils other than sands is limited. In this research indigenous, non-pathogenic and ureolytic bacterial strains were screened and isolated from the in situ soil. Four strains (Bacillus licheniformis, Rhodococcus erythropolis, Micrococcus luteus, and Lysinibacillus fusiformis) were selected based on their ability to grow at different temperatures, pH, soil moisture content and to precipitate CaCO3 through urea hydrolysis. For the implementation of the biocementation treatment, laboratory scale models were designed for pressure flow column and electrokinetic injection. The latter method was of particular interest in this study as a potential in situ implementation method under existing embankments. After a first series of pressure flow soil column experiments, with all strains, which studied parameters such as bacterial population and cementation reagent concentration and curing time. Following these, the best performing strain (Bacillus licheniformis) in terms of Unconfined Compressive Strength (UCS) and CaCO3 precipitation (in the flow column tests) was used for further testing and the electrokinetic experiments. Unconfined Compressive Strength (UCS) and oedometer testing results supported by CaCO3 measurements, NH4 + concentration measurements and pH change measurements, as well as microstructural SEM-EDS analysis, proved that biocementation did occur for both implementation methods and for a number of treatment combinations. EK was the most successful implementation method and was proven effective for degrees of saturation of 85-95%. Whilst treatment non-uniformity when bacteria were injected electrokinetically still needs to be addressed, there is promise that EK could be a viable technique for treating foundation soil under existing infrastructure, which is a major challenge for engineers