Microorganism in mitigating seismic liquefaction

Abstract

This thesis presents the results of a study in which Microbial Induced Calcite Precipitation (MICP) was used to improve the engineering behavior of the sandy soil for the purpose of mitigation of seismic liquefaction. MICP was attained using the urease positive microorganism isolated from the local garden soils. Those microorganisms were introduced to the specimens in a liquid growth medium consisting of urea and a dissolved calcium source. Two types of treatment methods were followed: method A and Method B. In method A, bacteria growth medium and additional cementation treatment solutions were applied into the specimens. In method B, bacteria and nutrient solution were mixed during the sample preparation by moist tamping method. Increase of pH and conductivity and decrease of Ca2+ ions of the treatment solution in method A confirmed urease activity. Increase of pressure in the pressure gauge of an experimental set up due to production of CO2 from the bio-treated soil when reacting with HCl, suggested that the observed cement bonds were comprised of calcite. Optical Microscope images confirmed the formation of calcite bonding with the sand particles. Improvement of the soil was assessed by unconfined compression tests, needle penetration tests and cyclic triaxial tests. Unconfined compression tests and needle penetration tests showed the increase in shear strength compared to untreated specimens. Cyclic triaxial tests with different cyclic stress ratio showed the increase of number of cycles to produce 5% double amplitude axial strain and/or zero effective stress compared to untreated specimens. As such, it could be concluded that MICP technique might be a useful tool for mitigation of seismic liquefaction.