Department of Civil and Environmental Engineering, University of Washington, Seattle, WA, 98195, USA.
Department of Microbiology and Molecular Genetics, University of California, Davis, CA, 95616, USA.
Sci Rep. 2023 Aug 30;13(1):14184. doi: 10.1038/s41598-023-41402-z.
Colloidal silica grouting is a ground improvement technique capable of stabilizing weak problematic soils and achieving large reductions in soil hydraulic conductivities for applications including earthquake-induced liquefaction mitigation and groundwater flow control. In the conventional approach, chemical accelerants are added to colloidal silica suspensions that are introduced into soils targeted for improvement and the formation of a semi-solid silica gel occurs over time at a rate controlled by suspension chemistry and in situ geochemical conditions. Although the process has been extensively investigated, controlling the rate of gel formation in the presence of varying subsurface conditions and the limited ability of conventional methods to effectively monitor the gel formation process has posed practical challenges. In this study, a biomediated soil improvement process is proposed which utilizes enriched fermentative microorganisms to control the gelation of colloidal silica grouts through solution pH reductions and ionic strength increases. Four series of batch experiments were performed to investigate the ability of glucose fermenting microorganisms to be enriched in natural sands to induce geochemical changes capable of mediating silica gel formation and assess the effect of treatment solution composition on pH reduction behaviors. Complementary batch and soil column experiments were subsequently performed to upscale the process and explore the effectiveness of chemical, hydraulic, and geophysical methods to monitor microbial activity, gel formation, and engineering improvements. Results demonstrate that fermentative microorganisms can be successfully enriched and mediate gel formation in suspensions that would otherwise remain highly stable, thereby forgoing the need for chemical accelerants, increasing the reliability and control of colloidal silica grouting, enabling new monitoring approaches, and affording engineering enhancements comparable to conventional colloidal silica grouts.
胶态二氧化硅灌浆是一种土壤改良技术，能够稳定软弱的问题土壤，并大幅降低土壤水力传导率，适用于地震引起的液化缓解和地下水流动控制等应用。在传统方法中，将化学促进剂添加到胶态二氧化硅悬浮液中，然后将其引入需要改良的土壤中，随着时间的推移，在悬浮液化学和原位地球化学条件控制下，半固态硅凝胶会逐渐形成。尽管该工艺已经得到了广泛的研究，但在不同的地下条件下控制凝胶形成的速率以及传统方法在有效监测凝胶形成过程方面的有限能力，都带来了实际挑战。在这项研究中，提出了一种生物介导的土壤改良过程，利用富含有机物的发酵微生物通过降低溶液 pH 值和增加离子强度来控制胶态二氧化硅灌浆的胶凝作用。进行了四组批处理实验，以研究葡萄糖发酵微生物在天然砂中富集的能力，从而引发能够介导硅凝胶形成的地球化学变化，并评估处理溶液组成对 pH 值降低行为的影响。随后进行了补充的批处理和土壤柱实验，以扩大该过程，并探索化学、水力和地球物理方法监测微生物活性、凝胶形成和工程改进的有效性。结果表明，发酵微生物可以在原本高度稳定的悬浮液中成功富集并介导凝胶形成，从而无需使用化学促进剂，提高了胶态二氧化硅灌浆的可靠性和可控性，为新的监测方法提供了可能，并提供了与传统胶态二氧化硅灌浆相当的工程增强效果。
