| 摘要: | 微生物引致碳酸鈣沉澱(Microbial induced calcite precipitation, MICP)提升砂土力學性質為近年發展的地盤改良工法之一，於砂土中添加微生物與營養液，透過生物新陳代謝作用析出碳酸鈣結晶體，該結晶體會沉澱於砂土孔隙，能有效地膠結砂土顆粒與填塞孔隙體積，可提升鬆砂土壤之剪力強度並降低滲透係數。此外，為加速呈現碳酸鈣沉澱之效果，以化學合成(碳酸鈉與氯化鈣混和溶液)方式模擬MICP改良後之狀態，並加以驗證。本研究先進行直接剪力試驗與無圍壓縮試驗，瞭解MICP與化學方法膠結土壤顆粒對土壤剪力強度改善程度，並由定水頭試驗測得改良前、後滲透係數差異，評估碳酸鈣結晶體填塞孔隙體積之有效性。最後，以離心模型試驗探討飽和鬆砂土層透過化學改良後的抗液化特性及其土層動態反應，評估碳酸鈣沉澱工法於現地施作之可行性。
試驗結果顯示，(1)MICP改良容易受到溫度及濕度等環境因素影響，但化學方法則能在短時間內完成碳酸鈣沉澱反應；(2)假單胞桿菌經由尿素酶催化作用後，在高濃度營養源條件下較能促進代謝反應，砂土試體在未改良前之凝聚力與摩擦角分別為0.8 kPa與35.0度，完全固化後則提升至24.2 kPa與38.2度，無圍壓縮強度達335 kPa，而由化學模擬亦能得到相近的試驗結果；(3)MICP與化學合成方法對砂土滲透係數改良效果皆不顯著，在營養液與模擬濃度1 M條件下，最大降低幅度僅為未改良前的0.85與0.81倍；(4)由離心模型動態試驗結果得知，碳酸鈣沉澱能固化飽和砂土層的改良範圍，受震時之加速度振幅比未改良區大，超額孔隙水壓比僅在初始振動階段上升至0.8後即快速消散，地表沉陷量小於未改良區，改良範圍於受震前後之土層剪力波速差異變化較小。
;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. |
