PDF(Pubmed)
Abstract：
Microbially induced nitrogen (N2) gas bubbles can desaturate subsurface areas and thus have been considered as an alternative ground improvement technique for mitigating soil liquefaction potential caused by earthquakes. However, the detailed mechanisms of subsurface N2 bubbles are not well understood and remain a subject of ongoing research. In this study, a transparent microfluidic device was utilized to mimic biological N2 gas bubble formation by nitrate-reducing bacteria and to visually characterize the entire process. During N2 gas formation, a limited number of bubble nucleation sites were identified, which gradually expanded upward through the preferential pore channels. N2 gas bubbles tended to create interconnected gas pockets rather than existing as evenly distributed small gas cavities. The degree of water saturation gradually reduced over a week as the bubbles were produced. The gas ganglia repeatedly grew until they reached the top boundary, which triggered a drastic expulsion of bubbles by ebullition. Despite fluctuations in saturation level, the residual saturation was maintained at around 73 %. Comparative experimental case studies of CO2 gas bubble formation were conducted to identify contrasting gas formation mechanisms. CO2 gas bubbles were generated via the abiotic decompression of a supersaturated CO2 solution under two distinct rates of pressure reduction. Rapid CO2 bubble formation led to uniform nucleation and 41 % residual saturation, while slower formation yielded 35 % due to stable liquid displacement by the gas front. This study highlights the potential of the microfluidic device as an experimental tool for visualizing subsurface gas formation mechanisms. The insights gained could further enhance and optimize geotechnical applications involving gas formation in highly saturated soils.
摘要：
微生物诱导的氮气（N2）气泡可以使地表下区域饱和，因此被认为是减轻地震引起的土壤液化潜力的替代地面改良技术。然而,地下N2气泡的详细机制尚未得到很好的理解，仍然是正在进行的研究的主题。在这项研究中,使用透明的微流体装置来模拟硝酸盐还原细菌的生物N2气泡形成，并在视觉上表征整个过程。在N2气体形成过程中,确定了有限数量的气泡成核位点，通过优先孔隙通道逐渐向上扩展。N2气泡倾向于产生互连的气穴，而不是作为均匀分布的小气腔存在。随着气泡的产生,水饱和度在一周内逐渐降低。气体神经节反复生长，直到它们到达顶部边界，这引发了泡沫的剧烈驱逐。尽管饱和度有波动,残余饱和度维持在约73%。进行了CO2气泡形成的比较实验案例研究，以确定对比的气体形成机理。CO2气泡是通过在两种不同的减压速率下对过饱和CO2溶液进行非生物减压而产生的。快速的CO2气泡形成导致均匀的成核和41%的残余饱和度，而较慢的形成产生了35%，这是由于气体前沿的稳定液体驱替。这项研究强调了微流体装置作为可视化地下气体形成机制的实验工具的潜力。获得的见解可以进一步增强和优化涉及高度饱和土壤中气体形成的岩土应用。
