Exploratory Investigation of Bio-inspired Flexible Calcite Precipitation for Soil Improvement

仿生柔性方解石沉淀用于土壤改良的探索性研究

• 批准号: 1638166
• 负责人: Muhannad Suleiman
• 金额: $ 16.27万
• 依托单位: Lehigh University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-08-01 至 2019-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1638166&HistoricalAwards=false
• 关键词: Exploratory; Investigation; Bio; inspired; Flexible

Civil infrastructures (e.g., highways, railroads, bridges, and buildings) are commonly constructed on weak and/or loose soils that require improvement to resist applied loads including those generated by natural hazards (e.g., earthquake loading). Often such soils are improved using energy-intensive materials and techniques that are not environment-friendly. These issues will be exacerbated over the next 25 years, as civil infrastructure is expected to expand greatly to accommodate an anticipated 30% growth in the world's population. To address these issues, sustainable and resilient materials and construction techniques must be developed. One such approach for soil improvement relies on bio-mediated processes that use indigenous bacteria (microbes) in the soil, with recent research focusing on the microbial induced carbonate precipitation (MICP) process. When comparing the responses of untreated and MICP-treated soils, the data available in the literature show that soil shear strength can increase by up to 500%. However, applications of the MICP technique have encountered challenges and difficulties including: (1) breakage of the brittle cementation bonds at small strains; (2) the generation of ammonium (a toxic waste product); and (3) limited penetration of microbes through the pores of soils smaller than fine sands. These challenges and difficulties (a) limit the MICP application to specific soil particle sizes and (b) reduce the shear strength and modulus of soils, which limits the benefits of the MICP technique in geotechnical applications such as liquefaction mitigation and foundation support. This grant promotes the progress of science by exploring the development of a new resilient and sustainable method to improve soil properties using a bio-inspired process that naturally occurs in sea sponges. This approach provides strong and flexible bonding of soil particles and can be used in finer soils. The proposed concept is transformative, and it accelerates the development of biogeotechnical soil improvement techniques, motivates further innovative developments in the field of bio-inspired geotechnical engineering, and enhances cross-disciplinary collaboration. The project also enables the training and education of undergraduate and graduate students, and in particular, will develop new researchers who are knowledgeable and competent in the techniques and procedures employed in biogeotechnical engineering that are not usually employed in traditional geotechnical engineering education; and educate the general public, K-12 teachers and students, university students, and practicing engineers. The goal of this project is to explore the concept of bio-inspired flexible calcite (BiFC) precipitation to improve the bonding (cementation), ductility, stiffness, and strength of soils. This research focuses on the use of the silicatein-alpha enzyme, without microbes, to induce flexible calcite precipitation in soils. Preliminary experiments demonstrated that the silicatein-á enzyme can precipitate bio-inspired flexible calcite (BiFC) in the laboratory and confirmed that BiFC with 10% to 16% silicatein á enzyme content has exceptional flexibility with no sign of breakage when subjected to strains greater than 20% with shear resistance that is 9 times greater than that of naturally-formed calcite. Therefore, it is hypothesized that using silicatein-alpha enzyme, without microbes, to produce BiFC precipitate in soils will eliminate the breakage of cementation bonds at small strains and enhance the mechanical properties of soils upon shearing (ductility, stiffness and strength), avoiding the need for additional healing treatments after earthquake loading. The proposed process also avoids the generation of ammonium that occurs with MICP; does not require subsurface stimulation or augmentation of microbes potentially reducing the cost of the process; and may extend the range of soil particle sizes that could be treated. To achieve the goal of the project, this exploratory research will focus on: (1) optimizing the production of silicatein-alpha enzyme and BiFC using bench-scale reactors and fermenters and characterizing BiFC using high-definition optical microscopy and scanning electron microscopy (SEM); (2) characterizing the micro scale mechanical properties of precipitated BiFC using Atomic Force Microscopy (AFM) cantilever beam tests and particle-scale tests; and (3) investigating the mechanical properties of BiFC treated sand and silt using triaxial testing.

民用基础设施（例如，公路、铁路、桥梁和建筑物）通常建造在需要改善以抵抗包括由自然灾害产生的载荷的软弱和/或松散土壤上（例如，地震荷载）。 这些土壤的改良往往使用能源密集型材料和技术，而这些材料和技术对环境不利。 这些问题将在未来25年内加剧，因为预计民用基础设施将大幅扩张，以适应预计30%的世界人口增长。 为了解决这些问题，必须开发可持续和有弹性的材料和建筑技术。 一种这样的土壤改良方法依赖于使用土壤中的土著细菌（微生物）的生物介导过程，最近的研究集中在微生物诱导的碳酸盐沉淀（MICP）过程。 当比较未处理和MICP处理土壤的响应时，文献中的数据表明，土壤剪切强度可增加高达500%。 然而，MICP技术的应用遇到了挑战和困难，包括：（1）在小应变下脆性胶结键的破坏;（2）铵（有毒废物产物）的产生;以及（3）微生物通过小于细砂的土壤的孔隙的有限渗透。 这些挑战和困难（a）限制了MICP应用于特定的土壤颗粒尺寸，以及（B）降低了土壤的剪切强度和模量，这限制了MICP技术在岩土工程应用（例如液化缓解和基础支撑）中的益处。 该赠款通过探索开发一种新的弹性和可持续的方法来促进科学的进步，以利用海绵中自然发生的生物启发过程来改善土壤特性。 这种方法提供了土壤颗粒的牢固和灵活的结合，并可用于较细的土壤。 提出的概念是变革性的，它加速了岩土工程土壤改良技术的发展，推动了生物启发岩土工程领域的进一步创新发展，并加强了跨学科合作。 该项目还能够对本科生和研究生进行培训和教育，特别是将培养新的研究人员，他们在传统岩土工程教育中通常不采用的岩土工程技术和程序中具有知识和能力;并教育公众，K-12教师和学生，大学生和执业工程师。 该项目的目标是探索生物启发的柔性方解石（BiFC）沉淀的概念，以改善土壤的粘结（胶结），延展性，刚度和强度。 这项研究的重点是使用silicatein-alpha酶，没有微生物，诱导灵活的方解石沉淀在土壤中。 初步实验表明，silicatein-á酶可以在实验室中沉淀生物激发的柔性方解石（BiFC），并证实具有10%至16% silicatein-á酶含量的BiFC具有优异的柔性，当经受大于20%的应变时没有断裂的迹象，其剪切阻力是天然形成的方解石的剪切阻力的9倍。 因此，假设在没有微生物的情况下使用silicatein-alpha酶在土壤中产生BiFC沉淀物，将消除小应变下胶结键的断裂，并增强剪切时土壤的机械性能（延展性，刚度和强度），避免地震荷载后需要额外的愈合处理。 所提出的方法还避免了与MICP一起发生的铵的产生;不需要潜在地降低该方法的成本的微生物的地下刺激或增强;并且可以扩展可以处理的土壤颗粒尺寸的范围。 为实现本项目的目标，本探索性研究将集中在：（1）使用实验室规模的反应器和发酵罐优化硅酸盐蛋白-α酶和BiFC的生产，并使用高清光学显微镜和扫描电子显微镜（SEM）表征BiFC;（2）使用原子力显微镜（AFM）悬臂梁测试和粒子-热分析表征沉淀BiFC的微尺度机械性能。（3）采用三轴试验研究了BiFC加固砂和粉土的力学特性。