| dc.description.abstract | Microbial induced calcite precipitation (MICP) is one of the ground improvement methods that can increase the mechanical properties of soil in recent year. By adding the bacteria and nutrient solution, the calcium carbonate crystals will be produced through the metabolism of microorganisms. The crystals will precipitate in the pores of sand, which can effectively cement the sand particles and fill the void volume; it can increase the shear strength and reduce the permeability. Also, in order to enhance the rate of calcite precipitation, using chemistry method simulates the specimen conditions improved by MICP method by adding Na2CO3-CaCl2 mixed liquid. Therefore, this study will conduct the direct shear test and the unconfined compression test to understand the performance of cementation in MICP and chemistry method. Also, from the constant head test, it can compare the difference in permeability before and after improvement, and evaluate the effectiveness of clogging by calcium carbonate crystals. Finally, using the centrifuge modeling test can know the liquefaction resistance and dynamic response before and after improvement; evaluate the feasibility of the calcium carbonate precipitation method to be applied in-situ construction.
According to the test results, (1) the MICP method may be affected by environmental conditions, including temperature or humidity, but the chemistry method can completely finish reaction in rapid time; (2) Pseudomonas sp can enhance the recreation of metabolism after ureolysis as increasing the nutrient concentration, the cohesion and friction angle of the specimens after solidified are increasing to 24.2 kPa and 38.2 degrees, the unconfined compression strength is 335 kPa. The chemistry method can also get almost the same or better test results than MICP method. (3) However, the permeability does not decrease obvious by those two methods, and the reduction rate are 0.85 and 0.81 respectively as compared with unimproved at 1 M of nutrients. (4) From the centrifuge modeling test results, calcium carbonate precipitation can enhance the effect of solidification on the improved area; the acceleration amplitude is higher than unimproved zone, and the excess pore water pressure ratio increases only to 0.8 at initial period and dissipates quickly. The unimproved zone has the larger surface settlement, thus it means that the shear wave velocity of improved area has the less difference as compared with before and after the seismic loading. | en_US |