Development of biocementation methods for sandy soil
Tan, Eugene Guan Long.
Date of Issue2011
School of Civil and Environmental Engineering
In the recent times, chemical grouting is being employed to improve mechanical strength of the soil formation and to reduce the soil hydraulic conductivity. However, there are disadvantages in adopting chemical grouting as means of soil improvement. Chemical grouting brings about environmental pollution to the surroundings as well as incurring high costs associated with machinery, equipments and chemicals. Hence for an alternative to chemical grouting, biological soil treatment in-situ would be a potential solution to overcome the shortcomings from chemical groutings. In this project on microbial induced calcite precipitation (MICP), it involves the study of the cultural liquid, cells suspension and enzyme solution being used as microbial medium for biocementation. Firstly, kinetic absorbent test for cells suspension and enzyme solutions in sand medium were carried out to determine whether cells suspension and enzyme solution can adhere to sand particles. Secondly, optimization of conditions such as pH, urease activities, concentration of ammonium ions and amount of calcium carbonate precipitation for cultural liquid, cells suspension and enzyme solution in biocementation conditions were carried out to attain optimal conditions for biocementation. Thirdly, treatment of sand samples were carried using cultural liquid, cells suspension and enzyme solution and results were compared between using pouring as a method for insertion of solution and injection as a method for insertion of solution. Sand treated with increasing number of cells suspension treatments show an increasing trend in both unconfined compressive and shear strength. The sand samples which underwent cells suspension treatment produced the highest unconfined compressive strength of 512 kPa. In addition, it has been observed that using pouring as an insertion method for the solution produces unconfined compressive strength that is 60 – 75% more than using injection as an insertion method for the solution. Lastly, experimental results also showed that by allowing each of the cultural liquid, cells suspension, enzyme solution and urea and calcium chloride solution to settle and react for one day after inserting into the sand sample would produce an uniform distribution of calcium carbonate precipitation along the depth of the sand sample. This could bring about a breakthrough in biocementation.
Final Year Project (FYP)
Nanyang Technological University