由微生物誘導碳酸鈣沉澱改良砂土之動態性質研究

Abstract

本研究旨在應用一種有效且環境友善的地盤改良技術——微生物誘導碳酸鈣沉澱法，於砂土改良上，瞭解其動態性質之變化。微生物誘導碳酸鈣沉澱法透過一系列生化反應促使方解石沉積於土壤孔隙中，藉此降低孔隙率與水力傳導性，顯著提升土壤強度。本研究以不同改良澆灌次數及不同養護齡期為主題，探討其對碳酸鈣沉澱行為與砂土動態力學性質之影響。實驗中改良液濃度固定為OD₆₀₀ = 1.0，養液採用0.5 M氯化鈣與0.5 M尿素等莫耳混合溶液。試體製備採單向注入方式，分別進行1、2、3與5次改良，其中改良1次與2次組設有7、14與21天養護條件，改良3次與5次者則固定養護7天。為評估微生物誘導碳酸鈣沉澱法改良效果，本研究亦以酸洗試驗、電腦斷層掃描與掃描式電子顯微鏡分析碳酸鈣沉澱量與分佈，並以共振柱試驗量測剪力模數與阻尼比等動態參數。試驗結果顯示，碳酸鈣沉澱量隨改良次數增加而顯著提升，顯示膠結反應可隨灌漿次數累積而增強。剪力模數亦隨養護齡期與改良次數提升而增加，反映碳酸鈣生成與結晶成長對土壤之勁度具有強化效果。阻尼比則於中高剪應變區顯現顯著提升，顯示膠結結構於變形過程中具有良好能量耗散能力。本研究確認了微生物誘導碳酸鈣沉澱技術在不同養護時間及多次改良條件下，能有效增強土壤動態力學性質，為地震易液化區域提供一種環境友善且永續的地盤改良解決方案。

This study aims to apply an effective and environmentally friendly ground improvement technique—Microbially Induced Calcite Precipitation (MICP)—to investigate the dynamic behavior of treated sandy soils. MICP promotes the precipitation of calcite within soil pores through a series of biochemical reactions, thereby reducing porosity and hydraulic conductivity, and significantly enhancing soil strength. The experimental program focuses on evaluating the effects of varying grouting frequencies and curing periods on calcium carbonate precipitation and the dynamic mechanical properties of sand. The treatment solution was prepared at a fixed bacterial concentration (OD₆₀₀ = 1.0), using an equimolar mixture of 0.5 M calcium chloride and 0.5 M urea. Specimens were prepared via unidirectional injection and subjected to one, two, three, or five treatment cycles. For one-time and two-time treatments, curing durations of 7, 14, and 21 days were adopted, whereas three-time and five-time treatments were cured for 7 days. To evaluate the effectiveness of microbially induced calcium carbonate precipitation (MICP), this study employed acid-washing tests, computed tomography (CT) scanning, and scanning electron microscopy (SEM) to analyze the amount and distribution of calcium carbonate. In addition, resonant column tests were conducted to measure dynamic properties such as shear modulus and damping ratio. The results show that calcium carbonate content increased significantly with the number of treatment cycles, indicating that the cementation reaction is accumulative. The shear modulus also increased with curing duration and treatment frequency, reflecting the strengthening effects of calcite formation and crystal growth. Moreover, notable enhancements in damping ratio were observed under medium to high shear strains, suggesting that the cemented structure effectively dissipates energy during deformation. This study confirms that MICP can effectively enhance the dynamic properties of sandy soils under varying curing times and multiple treatment cycles. It demonstrates the potential of this sustainable and eco-friendly technique as a viable ground improvement solution for liquefaction-prone regions.